From: Brian Lo <dragon@csulb.edu>
Newsgroups: rec.gardens
Subject: FAQ: Corn
Date: Wed, 1 Mar 1995 14:49:42 -0800
SWEET CORN
Zea mays
A number of genes affect sweetness in corn. These are recessive mutants
of the starchy gene found in field corn (Su) and their modifiers, and other
genes. Normal sweet corn has the recessive mutant of field corn (su).
Modifiers and other genes include the sugary-extender gene (se) and the
supersweet or shrunken gene (sh2). These make up three major genetic classes
of importance in commercial production :
Normal sugary (su) corn is the standard corn grown for processing and
much of the fresh market. The seed germinates well at 55-60 F.
Sugary enhanced (se) corn results in slightly increased sugar levels and
slower conversion of sugars to starch after harvest. Kernels are very tender
with good "corn" flavor. Seed germinates well at temperatures of 55-60 F.
Super sweet or extra sweet (sh2) corn produces kernels with two to three
times the complex sugars of the standard corn varieties. Texture is crispy
rather than creamy as with the standard and enhanced varieties. Fresh market
shelf life is extended due to the ability of the kernels to retain moisture.
Seed kernels are smaller, lighter in weight and shrunken in appearance (giving
the gene the name "shrunken").
XENIA:
Xenia effects are pollen induced changes in kernels of sweetcorn
apparent on the ears to be harvested. Some of these changes may be intended
and beneficial. These changes are of most concern when they result in a loss
of cob or kernel quality by adversely changing kernel color, kernel weight,
embryo weight, soluble solids percent, pericarp texture and content, kernel
moisture and cause other undesirable direct and indirect effects. A number
of ways to manage xenia effects are used. The main method is by isolation of
the different genotypes. Consult sections on isolation as explained below.
RECOMMENDED VARIETIES (approximately 70 days for early and 100 days for main
season varieties in the Willamette Valley, warmer areas, 7-10 days less).
YELLOW KERNELS:
Standard sweet (su) very early: Northern Vee; early: Sundance; main
season: Jubilee (also called Golden Jubilee), Commander and Stylepak (the
latter three are used for processing) and all are used for fresh market.
Super Sweet (sh2), Early: Flare, Summer Sweet 6700, Butterfruit,
Party-Time. Main season: Supersweet Jubilee, Challanger, Stylesweet, Crisp'N
Sweet 710, For trial: Excel, Fanciful, Showcase, Pinnacle, Sweet Treat, Illini
Gold, Summer Sweet 7200, Zenith.
"Improved Super Sweets" (sh2,su): Sweetie 82.
Sugary enchanced (su,se) very early: Sugar Buns; early: Honey Buns,
Precocious, Bodacious, Miracle; main season: Incredible, Tendertreat and
Kandy Korn.
WHITE KERNELS (must be isolated from yellow or bicolor types):
Standard sweet (su): Silver Queen, Sterling.
Supersweet (sh2): How Sweet It Is, Summer Sweet 8601. For trial: Aspen.
Sugary enhanced (su,se): Divinity, Alpine, Snowbelle, Silverado, White
Lightning, Platinum Lady.
BICIOLOR KERNELS:
Standard sweet (su): Dandy, Harmony, Honey and Cream, Sweet Sue, Double
Taste.
Supersweet (sh2): Honey and Pearl; Phenomenal.
Sugary enhanced (su,se): Calico Belle; Double Delight.
NOTE: Kernel quality of all the above varieties may be dramatically
altered under certain pollination conditions. See the sections below on
"Genetic types" and "Isolation".
POP CORN (Su; approximately 110 days); white, yellow, red and black
kernel types are available. Only white and yellow are of commercial impor-
tance:
White Cloud, Crookham 1084.
ORNAMENTAL CORN (Su; approximately 100 days):
Chinook, Indian Ornamental and Fiesta are standard size cobs; Wampum,
Indian Fingers and Strawberry Popcorn are small or miniature cob types.
BABY CORN: All baby corn is hand harvested and hand husked from
immature corn at, or within 1-2 days after silking. The main varieties used
are either prolific (multiple-eared) starchy feed corn types (Su), or super-
sweet (sh2). Research indicates the quality (sweetness and crispness) is
equally good for all genotypes, but that yields are higher with prolific
(multi-eared) starchy types. Varieties with small kernels and long ears are
particularly suited. The pickled baby corn imported from Taiwan and Thailand)
is produced from special field corn (Su) varieties developed there for that
purpose such as Tainan No. 5, Tainan No. 11, Tainung No. 351, or a superweet
corn such as Florida Staysweet (sh2). Other varietes that are suggested for
trial are the white kernel variety Silver Queen, the yellow kernel supersweet
varieties Stylesweet and How Sweet It Is, and the variety Baby Corn (Su a type
of Japanese hulless popcorn), are suggested for this purpose. Tom Thumb,
Golden Midget, and Miniature Hybrid may be others.
SEED COMPANIES
Abbott & Cobb Inc. POB F307, Feasterville, PA 19047
Asgrow Seed Company, POB 5038, Salinas CA 93915
Crookham Co. Caldwell, ID 83606
Ferry-Morse Seed Co. POB 4938, 555 Codoni Ave. Modesto, CA 95352
Harris Moran Seed Co. 3670 Buffalo Rd. Rochester, NY 14624
Illinois Foundation Seeds Inc. POB 722, Champaign, IL 61820
Rogers NK Seed Co. POB 4727, Boise, ID 83711-4727
Stokes Seeds Inc. POB 548, Buffalo, NY 14240
Sunseeds, 2320 Technology Pkwy. Hollister, CA 95023
W. Osborne Seed Co. Int'l. 1679 Highway 99 South, Mount Vernon, WA 98273
Zenner Bros. Seed Co., Inc. 1311 S.E. Gideon St. Portland, OR 97202
GENETIC TYPES:
The threee genetic classes mentioned above are categorized into 6 major
sugar mutant types. Other categories exist, but are not of commercial
importance. These may be represented by yellow, white, or bi-color varieties.
The following table modified from a paper by J.W. Courter and others,
describes these table corn types and classifies them into categories for
isolation purposes:
ISOLATION DESCRIPTIVE HOMOZYGOUS VARIETY
CLASS TERMINOLOGY RECESSIVE EXAMPLES
"SUGAR" GENES
I Field, dent, or flour corn none
II*a Sugary or standard sweet corn su Jubilee (yellow)
Double Taste (bicolor)
Silver Queen (white)
II*b Sugary augmented with su se Kandy Korn EH (yellow)
sugary enhancer; or heterozygous D'Artagnan (bicolor)
"EH" types Siverado (white)
su se Miracle (yellow)
homozygous Calico Bell (bicol)
(no whites)
II*c Sugary augmented with su sh-2 Sugar Loaf (yellow)
shrunken-2; or heterozygous (no bicolors)
"SWEET gene HYBRID", or (no whites)
"Synergistics"
III**a Shrunken-2, supersweets, or sh-2 Crisp N Sweet 710 (y)
"Xtra-Sweet" hybrids Honey and Pearl (bi)
How Sweet It Is (wht)
III**b Shrunken-2 augmented with sh-2 su Sweetie 82 (yellow)
sugary; or "Improved heterozygous (no bicolors)
Supersweet Hybrid" (no whites)
* Class II contains varieties homozygous only for su (IIa) as well as
those homozygous su cultivars with additional heterozygous OR Homozygous
recessive genes such as se (IIb), or sh2 (IIc), since cross pollination of
such cultivars will still produce su kernels (sweetcorn).
** Class III contains varieties homozygous only for sh2 (IIIa) as well
as those homozygous sh2 cultivars with additional heterozygous recessive genes
such as su (IIIb), since cross pollination of such cultivars will still
produce sh2 kernels (supersweet corn).
A recommended isolation distance, in feet, is given in the following
table for the different classes of corn. Popcorn and ornamental Indian corn
should be considered as two additional, separate, isolation classes.
White-kernel varieties must be isolated from all other corn by 500 feet or
more. See also the ISOLATION section on page 4 for a further discussion on
this:
ISOLATION DISTANCE RECOMMENDED (ft.)
ISOLATION
CLASS I IIa IIb IIc IIIa IIIb
I 0 250 250 250 250 250
IIa 250 0 50 50 250 250
IIb 250 50 0 50 250 250
IIc 250 50 50 0 250 250
IIIa 250 250 250 250 0 50
IIIb 250 250 250 250 50 0
Note: An isolation distance of 250 feet is given between isolation
classes I, II, and III, wherever outcrossing will cause flavor, texture, and
the starch content of the outcrossed kernels to resemble field corn. Popcorn
and ornamental Indian corn should be considered as two additional isolation
classes to be separated from all isolation classes by 250 feet.
An isolation distance of 50 feet is given whenever outcrossing is not
very detrimental but could result in flavor, texture, and the starch content
of the outcrossed kernels to be no different than the un-augmented type
(sugary in class II and supersweet in class III).
ISOLATION:
Isolation is necessary from two points of view, color and kernel quality
(sugars and texture). Since colored kernels in white varieties are very
obvious, a 500 foot or more isolation distance is recommended between white
and colored varieties. A two week difference in silking may also be used, but
is less reliable. For isolation regarding kernel quality considerations the
following is recommended:
Supersweet corn varieties and other new types of corn requiring isola-
tion from standard sweet types (discussed above in the "VARIETIES" section)
should be isolated based on their Isolation Class categorization. The use of
2-4 border rows helps minimize contamination in all situations described
below. Isolation may be accomplished in three ways, by distance, time of
pollination, and blocking. Isolation by distance is the preferred method.
Isolation by distance:
Observations at Oregon State University over several seasons indicate
that if no isolation is used between standard sweet (Isolation Class II) and
supersweet types (Isolation Class III), outcrossing of kernels in adjacent
rows, and extending for 6 to 10 rows into each type is high enough to render
the ears from these rows unsalable. This outcrossing can result in over 50%
of the kernels on ears in adjacent rows being starchy. Outcrossing drops off
rapidly beyond 10 rows, until at about 100 feet, only up to 1% of kernels (up
to 4 kernels per ear) may be starchy. This level of outcrossing is probably
not discernible by fresh market buyers or consumers. Processing companies
however may have different requirements for isolation.
Where large plantings are made for fresh market production, a distance
of 250 feet is recommended between Isolation Classes I, II, and III. Where
isolation of fields is convenient, maximum isolation would not need to exceed
600 feet, which is a conservative assumption based on distances used for seed
production, where isolation is even more important. Whenever practical:
1. Locate supersweet varieties (Isolation Class III) upwind of variet-
ies in all other isolation classes since outcrossed kernels may be more
apparent in the supersweet ears.
2. Mechanically top standard sweet plantings, of the variety Jubilee,
two leaves above the top ear after the silks have turned brown, and before
nearby supersweet plantings begin to silk. Topping an earlier nearby super-
sweet planting, or a standard sweet variety other than Jubilee would also be
helpful, but timing and the effect of topping on yields of super- sweet corn,
and other standard sweet varieties, have not been researched adequately.
Unacceptable reductions in yield have been observed in limited research on
topping of other varieties (see also section on TOPPING below).
3. In small sequential fresh market plantings, plant all varieties of
one Isolation Class (I, II, OR III) together in a block located 250 feet or
more from a block containing sequential plantings of varieties of any other
Isolation Class. For best quality results, varieties of different subclasses
(IIa, IIb, OR IIc) should be isolated 50 feet from other subclasses within the
same Isolation Class.
Isolation by time of pollination:
If the 2-3 week pollination time difference is to be used as a means of
isolation between Isolation Classes, and plantings of different Isolation
Classes are adjacent, several things need to be considered:
1. The later planting must not be planted based on calendar day diff-
erence, but rather on growth stage or heat units. Specifics on this need to
be obtained from the individual seed company regarding their variety. The
maturity difference between the two types of corn has to also be figured into
the planting date difference. Assuming the standard sweet (Isolation Class
II) and supersweet (Isolation Class III) varieties have the same maturity
(days from seeding to pollination), delay planting the other Isolation Class
of corn until the first planting has 8 or more leaves, or 300 or more heat
units (base 50 F) have elapsed.
2. To obtain an effective two to three week spread at pollination, the
early planting must germinate uniformly or else late germinating plants may
cause problems.
3. Whenever possible, mechanically top the early planting just before
the later one begins to silk (CAUTION, see section on TOPPING below). Fresh
market growers may choose to hand-top the late flowering plants or suckers in
10 or 20 rows adjacent to the later planting. Be especially careful of late
flowering suckers in these rows.
Isolation by blocking:
Fresh market growers who have a use for, or a market for ensilage, may
also choose to "block" plantings that have not been isolated by distance or
pollination time. This practice consists of walking progressively further
from the boundary of the two plantings, examining a sample of ears in each row
visually until one finds the row where the outcrossing incidence is accept-
able, abandoning the intervening rows (and using them for silage). In
Florida, experience has shown that 6-10 rows (sometimes up to 20 rows) may
need to be skipped.
SOIL
A wide variety of soils are suitable. It is important that the soil be
well drained and well supplied with organic matter. The optimum pH range is
5.8 to 7.0.
SOIL TEMPERATURE
The optimum soil temperature range for germination is over 60 F. This
is especially true for the super sweet and improved super sweet varieties
where germination may be drastically reduced under cool soil conditions.
Sweet corn takes about 20 days to emerge from 50 F soils, but only about 5
days to emerge at 70 F. Soil temperature is one factor in scheduling plant-
ings.
SEED AND SEED TREATMENT
Sweet corn seed numbers approximately 120-180 per ounce. About 10-15
lbs. are used per acre. Use only seed treated with fungicides and insecti-
cides. Some seed companies are now offering super sweet varieties with
specially coated, sized seed, intended to improve stand establishment.
Research indicates that seed shape and size are related to emergence and
stand establishment and performance. In normal sweet corn, flat seed perform
better than round, and in both classes, high density seeds perform better than
those of lower density.
When planting supersweet varieties, large differences in seed vigor
occur between different varieties, particularly under cool, wet or compacted
soil conditions. The difference in performance is not apparant from germina-
tion information on the identification tags.
SEEDING
For early fresh-market standard varieties, seeding may start as soon as
soil temperature reaches 60 F. In western Oregon, this is generally about the
end of April, and planting extends through June.
In eastern Oregon, depending on location, planting may start about 2
weeks earlier and may extend into mid July. Care should be taken that sweet
corn is planted after the danger of spring frost has passed.
Use 10-15 lb./acre of seed, depending on the variety and seed size.
Seeding at a depth of l-2 in. is generally satisfactory. Shallow planting
(1/2 in.) and maintenance of high soil moisture is recommended where head smut
may be a problem, and for supersweet types. For processing, recommended
stands are 26,000 to 27,000/A while for fresh market, where large ear size and
good husk color are important, stands should be between 20,000 and 25,000 per
acre.
A rough planting schedule that would provide about 10-14 days between
mid season peak harvests between plantings would be to wait till most of the
plants in the previous planting had 3 leaves before making the next planting.
SPACING:
Plant quick-growing, small stature varieties in rows approximately 30
in. apart, and 6-8 in. in the rows. Vigorous tall-growing varieties should be
grown in rows 30-36 in. apart, 9-12 in. between plants. Processing varieties
should be planted according to the row spacing and rate required by the
processor.
For baby corn two systems are used. One system uses standard populations
of about 23,000 plants per acre, where the top ear is left on the plant for
grain corn or sweet corn, and subsequent ears harvested for baby corn. The
second system uses high plant populations of between 34,000 and 44,000 plants
per acre where all ears are harvested for baby corn. Row spacings range from
24-36 inches apart. The standard plant populations produce yields of about
4,000 lbs. of unhusked ears (400 lbs of husked ears) per acre, while the high
populations produce yields of about 8,000-10,000 lbs. of unhusked ears (800-
1000 lbs. of husked ears) per acre.
BIRD CONTROL
For bird control, including pheasants, use Mesurol 50% Hopper Box.
Treatment - 0.25 to 0.5 lb/l00 lb. seed. Reduces feeding damage to seeds and
seedlings.
FERTILIZER
A soil test is the most accurate guide to fertilizer requirements. The
following are general guidelines:
Western Oregon:
Good management practices are essential if optimum fertilizer responses
are to be realized. These practices include use of recommended varieties,
selection of adapted soils, weed control, disease and insect control, good
seed bed preparation, proper seeding methods, and timely harvest.
Recommendations are based on a 36" row spacing. With decreased row spa-
cings fertilizer rates should be increased by 10% for each 3" decrease in row
spacing.
An early irrigation when corn is about 6" high will insure most effi-
cient utilization of banded fertilizer.
Recommended soil sampling procedures should be followed in order to
estimate fertilizer needs. The Oregon State University Extension Service
agent in your county can provide you with soil sampling instructions and soil
sample bags and information sheets.
NITROGEN (N):
The rate of N application depends on the carry over of N from the pre-
vious crop:
Previous N application
crop lbs/A
Grain 200-225
Corn, snap beans, poor clover or alfalfa 150-175
Good clover or alfalfa 100-125
On coarse textured sandy or gravely soils such as the Sifton soil
series, 225 to 250 lb/A of N may be required.
About 50 lbs N/A should be banded with the P fertilizer at planting
time. The remainder of the N may be applied before planting and/or during the
growing season before plants are 3 ft tall. The later application of N is
suggested where there is a potential for leaching such as with early plantings
and on sandy or gravely soils. The application of 25% of the N when corn is
12" tall has given good results.
If the application of N plus potash (K2 O) exceeds 90 lb/A, there is
danger of seedling in jury from the concentration of salt when fertilizer is
banded at planting time.
Fertilizer salt injury can be reduced by using two rather than one
fertilizer band, not banding too close to the seed, and immediate irrigation
at first sign of crop injury. Salt injury is likely to be greater in sandy
soil compared to finer textured soil and in dry soil compared to moist soil.
PHOSPHORUS (P)
Phosphorus is essential for vigorous early growth of seedlings. All of
the P should be banded 2 to 3" to the side and 2-3" below the seed when
planting.
Response is greatest from bands properly placed at 2" x 2".
If the OSU soil test Apply this amount of
for P reads (ppm): phosphate (P2 O5) (lb/A):
0 - 15 120 - 150
15 - 50 80 - 120
Over 50 60 - 80
These P recommendations assume that the soil pH is 5.8 or higher and
that corn is planted by mid-May. Reduce P rates by 1/3 for June plantings.
When soil pH is below 5.6 and lime is not applied, P rates should be in-
creased.
POTASSIUM (K)
Potassium should be broadcast and plowed down before planting or banded
when planting. Not more than 60 lb/A of K2 O should be banded. The total of
N + K2 O in the fertilizer band should not exceed 90 lbs/A.
If the OSU soil test Apply this amount of
for K reads (ppm): potash(K2 O) (lb/A)
0 - 100 100 - 150
100 - 200 50 - 100
Over 200 None
SULFUR (S)
Plants absorb S in the form of sulfate. Fertilizer materials supply S
in the form of sulfate and elemental S. Elemental S must convert to sulfate
in the soil before the S becomes available to plants. The conversion of ele-
mental S to sulfate is usually rapid for fine ground (less than 40 mesh)
material in warm, moist soil.
The S requirements of sweet corn can be provided by:
1. The application of 15-20 lb/A of S in the form of sulfate at plan-
ting time.
2. Applying 30-40 lb/A of S as fine ground elemental S the preceding
year.
3. Applying coarser ground elemental S at higher rates and less
frequently.
Some S fertilizer materials such as elemental S and ammonium sulfate
have an acidifying effect on soil.
MAGNESIUM (Mg)
Magnesium applications are recommended when soil test values for Mg are
below 1.0 meq Magnesium/100g of soil or when the calcium (Ca) soil test value
is more than 10 times the Mg value.
Band 10 to 15 lbs/A of Mg when planting. If deficiency symptoms appear,
spray with 10 lbs/A of Epsom salts in 100 gals of water.
Magnesium can also be supplied in dolomite, which is a liming material
that reduces soil acidity to about the same degree as ground limestone. Dolo-
mite should be mixed into the seedbed several weeks in advance of seeding.
BORON (B)
No consistent responses of sweet corn to the application of B have been
observed in western Oregon.
Where the soil test value for B is below 0.25 ppm, growers may wish to
make a trial application of 2 lb/A of B.
Too much B fertilizer can be highly toxic; therefore, suggested rates of
B application should not be exceeded and B should be evenly distributed over
the field and not be banded at planting.
Boron and fertilizer materials should be thoroughly mixed when B appli-
cation is combined with other fertilizers.
ZINC (Zn)
The application of Zn has increased the yield of sweet corn in the
Stayton area especially on the gravely, dark colored soils.
If the OSU soil test Apply this amount
for Zn reads (ppm) of Zn in lbs/A
less than 1 3 - 4 banded; or 10 broadcast
Over 1 0
When the soil test is below 1 ppm Zn, a response to Zn is expected on
all soils.
When the soil test is between 1 and 1.5 ppm Zn a response to Zn is
expected on most soils in the Stayton area.
Where Zn is required, either 10 lbs/A of Zn should be broadcast and
worked into the soil prior to planting or 3 to 4 lbs/A of Zn should be banded
with the fertilizer at planting time. A broadcast application of 10 lbs Zn/A
should supply Zn needs for 2 or 3 years.
Responses of sweet corn to nutrients other than those discussed in this
guide have not been observed in western Oregon.
LIME
Experimental work has shown that sweet corn will produce good yields
over a fairly wide range of soil acidity.
Lime applications are suggested when the soil pH is below 5.8 or when
calcium (Ca) levels are below 5 meq Ca/100g of soil.
The rate of lime application can be estimated from the following OSU
lime requirement table:
If the OSU SMP Buffer Apply this amount
test for lime reads of lime (T/A):
Below 5.6 4 - 5
5.6 - 5.8 3 - 4
5.8 - 6.0 2 - 3
6.0 - 6.3 1 - 2
Over 6.3 0
The liming rate is based on 100-score lime.
Lime should be mixed into the soil at least several weeks before plan-
ting and preferably the previous fall. A lime application is effective over
several years.
Some soils may have a fairly high OSU SMP buffer value (over 6.2) and a
low pH (below 5.3). This condition can be caused by the application of
acidifying fertilizer. In this case the low pH value is temporary and the pH
of the soil will increase as the fertilizer completes its reaction with the
soil. This temporary "active" acidity from fertilizer is encountered follow-
ing recent applications of most nitrogen fertilizer materials.
Acidifying fertilizers also have a long term acidifying effect on soil
which is cumulative and leads to lower OSU SMP buffer readings.
Sandy soils to which fertilizers have not been recently applied some-
times record low pH and high SMP buffer values. In such cases, a light appli-
cation of lime (1 to 2 T/A) should suffice to neutralize soil acidity.
For acid soils low in magnesium (less than 1.0 meq magnesium/100 g.
soil), 1 T/A of dolomite lime can be used as a Mg source. Dolomite and ground
lime stone have about the same ability to neutralize soil acidity.
Fertilizer Guide #3, "Liming Materials for Oregon," which is available
from your local OSU Extension Office, provides additional information on lime.
Phosphorus, K, Mg, B, Zn, and lime suggestions are based on soil test
values from the Soil Testing Laboratory, OSU, Corvallis, Oregon.
These guides to fertilization are largely based on the results of expe-
riments conducted by Horticulture and Soils Department scientists of the
Oregon Agricultural Experiment Station and are quoted from O.S.U. Fertilizer
Guide FG11.
Eastern Oregon:
The fertilizer applications suggested in this guide are based on a
population of 25,000 to 30,000 plants/A. Fertilizer rates can be adjusted
proportionately up or down when plant population and predicted yield deviate
from these values.
NITROGEN (N)
Sweet corn requires a good supply of available N. An optimum response
to N fertilization depends on adequate irrigation. An irrigation when corn is
12-18" high will insure most efficient utilization of banded fertilizer.
Part (40-60 lbs/A) of the N should be banded at planting time the
remainder may be applied before planting and/or during the growing season
before tasseling, particularly where leaching is likely to be a problem.
If the band application of N exceeds 60 lb/A, there is danger of seed-
ling injury from the concentration of salt.
Fertilizer salt injury can be reduced by using 2 rather than 1 fertili-
zer bands, not banding too close to the seed, and immediate irrigation at
first sign of crop injury. Salt injury is likely to be greater in sandy soil
compared to finer textured soil and in dry compared to moist soil.
The urea or diammonium phosphate forms of N may cause seedling injury if
banded close to the seed at planting, especially where the soil pH exceeds
7.0.
Amount of N fertilizer required depends on the following factors:
The preceding crop; the N carry-over from the previous crop; the amount
and type of residue to be plowed under; and possible leaching losses due to
over-irrigation.
The following fertilizer guides are for mineral soils with low organic
matter content.
N Fertilizer Guide Based on Soil Test
The amount of residual N in the soil varies considerably. A soil test
for nitrate-N helps in evaluating the N carry-over from the previous crops in
the case of mineral soils with low organic matter content. Soil samples for
Nitrate-N should be taken following a growing season and prior to the applica-
tion of N fertilizer.
Soil samples should be taken from 0-2' and 2-5' depths on deep soils.
The soil samples should consist of soil cores removed from the entire 0-2' and
2-5' depths of soil. On soils shallower than 5', soil samples should be taken
from 0-2' and from 2' to the expected rooting depth.
OSU soil test results for N are reported in ppm. One ppm N in a 1'
depth of soil equals about 4 lbs N/acre. As an example:
Soil depth Nitrate-N
(ft) (ppm) (lbs/A)
0 - 2 4 32
2 - 5 3 36
Total 68 lbs/A
The total Nitrate-N soil test values are used to estimate the N ferti-
lizer requirement as follows:
After* After
Nitrate-N Soil non-legume beans, peas
Test (lbs/A) crop or alfalfa
0 300 250
50 250 200
100 200 150
150 150 100
200 100 50
250 50 0
300 0 0
*When straw is incorporated after Sept. 1, in crease N fertilizer rate
by 30-50 lbs/A.
Should the soil test value for Nitrate-N be less than 2 ppm in the 0-2'
soil depth apply a mini mum of 30 lbs N/A regardless of the soil test value
for N below 2'. This application is to insure adequate initial growth of
plants.
PHOSPHORUS (P)
Phosphorus is essential for vigorous early growth of seedlings. All of
the P should be banded 2" to the side and 2" below the seed at planting.
If OSU soil test Band this amount* of
for P reads (ppm) phosphate(P2 O5) (lbs/A)
0 - 5 100 - 150
5 - 12** 0 - 100
*Double the rate of P application when P is plowed down.
**For early plantings into cool soil when P soil test exceeds 12 ppm,
apply 20-30 lbs P2O5/A in a 2"x2" band.
POTASSIUM (K)
Potassium should be broadcast and plowed down before planting.
If the OSU soil test Apply this amount of
for K reads (ppm): potash (K2 O) (lbs/A)
0 - 100 150 - 200
100 - 150 100 - 150
150 - 200 0 - 100
SULFUR (S)
Plants absorb S in the form of sulfate. Fertilizer materials supply S
in the form of sulfate and elemental S. Elemental S must convert to sulfate
in the soil before the S becomes avail able to plants. The conversion of
elemental S to sulfate is usually rapid for fine ground (less than 40 mesh)
material in warm moist soil.
Elemental S should be applied the year preceding the crop using finely
ground (less than 40 mesh) material. Elemental S is a strong soil acidifier.
S in the sulfate form can be applied at planting time.
If OSU soil test for Apply this amount of S*
SO 4 - S in the 0-2' in lbs/acre:
soil depth reads (ppm) Loamy soil Sandy soil**
0 - 2 20 - 30 30 - 40
2 - 5 0 - 20 20 - 30
5 - 8 0 0 - 20
*When the irrigation water contains over 2 ppm of S, additional S fer-
tilizer is probably not required.
**These rates should be increased by 50% for sandy soils in central
Oregon.
S requirements will vary with soil texture, leaching losses and the soil
parent material. S is frequently contained in fertilizers used to sup ply
other nutrients such as N, P, and K and may be present in irrigation water
which can be tested for S content.
ZINC (Zn)
Sweet corn has a relatively high requirement for Zn. An application of
Zn is suggested when the Zn soil test value is below 0.8 ppm.
Where Zn is required, either 10 lb Zn/A should be broadcast and worked
into the soil prior to planting or 3 to 4 lb Zn/A should be banded with the
fertilizer at planting time. An application of 10 lb Zn/A should supply Zn
needs for 2 or 3 years.
To correct Zn deficiency during the growing season thoroughly wet plants
with a solution containing 1 lb Zn in 50 to 100 gal of water.
BORON (B)
Responses of sweet corn to B have not been observed in eastern Oregon.
Where the soil test value for B is below 0.4 ppm trial applications of B are
suggested.
OTHER NUTRIENTS
Responses of sweet corn to other nutrients such as copper and iron have
not been observed in eastern Oregon.
LIME
Responses of sweet corn to lime have not been observed in eastern Ore-
gon; however, where the soil test pH value is less than 5.5 a lime application
is suggested. Soil pH should be measured prior to application of fertilizer.
Where the subsoil is calcareous or has a higher pH deep plowing will
reduce surface soil acidity.
On sandy soils where soil acidity is most prevalent, one ton of dry
100-score lime raises the pH about 1 unit. In most instances 1 to 1 1/2 T/A
of lime is adequate to correct soil acidity. With silt loam and clay loam
soils 2 to 3 T/A of lime respectively will raise soil pH about one unit.
Lime should be mixed into the seedbed at least several weeks before
seeding. A lime application is effective over several years.
The liming rate is based on 100-score lime.
SUFFICIENCY LEVELS FOR SWEET CORN
Data from the midwest indicates the following sufficiency levels for
sweetcorn based on growth stage (from the National Corn Handbook, NCH-43):
Nutrient Sufficiency Levels in Sweet Corn
------------------------------------------------------------------------------
Growth Plant Part N P K Ca Mg S Fe B Zn Mn Mo
Stage Sampled
------------------------------------------------------------------------------
12 in. whole plant 3.5 0.4 3.0 0.3 0.30 0.2 50 7 20 50 0.3
Silk ear leaf 2.8 0.25 1.8 0.3 0.25 0.2 60 6 20 25 0.3
------------------------------------------------------------------------------
Levels below these values are considered low or deficient. Levels
above these values are considered high or excessive.
------------------------------------------------------------------------------
The above values should be used as guides only for diagnostic purposes.
Such values may differ for different varieties.
SALTY SOILS
The growth of sweet corn will likely be restricted when the soil test
value for soluble salts exceeds 4 mmhos/cm.
The eastern Oregon guides are largely based on the results of experi-
ments conducted by Washington State University and observations of growers'
fields, and have been quoted and modified from OSU Fertilizer Guide No. FG71.
IRRIGATION
For western Oregon 12-14 inches of water provides optimum yields and ear
size. In eastern Oregon 25-28 inches may be needed depending on seasonal
variation, variety and planting date. Approximate summer irrigation needs for
the Hermiston area have been found to be: 3.5 inches in May, 5.0 in June, 7.5
in July, and 7.0 in August.
Soil type does not affect the amount of total water needed, but does
dictate frequency of water application. Lighter soils need more frequent
water applications, but less water applied per application.
To facilitate movement of irrigation pipe at the last irrigation/s,
expedite harvest, and to reduce lodging, corn may be topped after pollination
is completed (see section on TOPPING below).
TOPPING
Corn is sometimes topped to facilitate movement of hand carried irri-
gation pipe through the fields, expedite harvest, and to reduce danger of
lodging. Topping is done by special high clearance machines that use rotary
cutting blades.
Top corn when pollination is completed (2/3 to 3/4 of silks of top ears
begin to turn brown), and leave 2-3 leaves above the top ear, otherwise yields
will be unacceptably reduced. Topping at the correct time may still result in
up to a 10% yield reduction but this is usually compensated for by better
irrigation, expeditious harvest, and reduction in lodging. This topping
information has been developed for the variety Jubilee. Other varieties may
have yields seriously depressed by topping (Stylepak), or may have silks that
do not turn brown after pollination, making this timing indicator unsuitable.
For "baby corn" production, when using a dwarf variety like Tom Thumb,
cut the entire plants off 2 inches above ground level, after the first main
stalk ears are harvested, and allow the crown to regrow as many new shoots as
possible. This will produce additional suckers and shoots and result in more
ears being produced for further pickings.
HARVESTING, HANDLING, AND STORAGE
In western Oregon, sweetcorn harvest ranges from about early August to
mid October. The prime harvest season is from about August 25th. to the end of
September.
In eastern Oregon harvest ranges from about mid July to the end of
October with the prime harvest season being from about the first of August to
the end of September.
Sweetcorn yields can range widely. Early, small-eared corn yields can
be approximately 80 cwt./acre, while main-season varieties yield approximately
130 cwt./acre, or about 300 crates/acre. Processing sweetcorn average yield
is approximately 9 tons/acre with good yields about 12-14 tons/acre.
For optimum quality and returns, harvest of standard sugary (su) and
sugary-extender (se) varieties begins when kernels reach 70-75% moisture.
Supersweet (sh2) varieties have a much higher sugar content than su or se
varieties and maintain their sugar content longer after harvest. They are
usually harvested at 77-78% moisture.
Kernel moisture drops approximately 0.5% per day in normal sweet and
sugary extender corn varieties with considerable variation depending on season
and variety. Kernel moisture of supersweet (sh2) varieties changes at a
slower rate. All sweetcorn, regardless of type, requires immediate cooling
and refrigerated transport and handling. Corn intended for processing should
be protected from overheating and delivered to the processor as soon as
possible.
Limited Oregon research data indicate that there is approximately a
0.356 tons per acre increase for each decrease in 1% kernel moisture, with
considerable variation depending on season and cultivar (ranging from 0.173 to
0.792 T/A over 5 seasons and 9 varieties). Supersweet (sh2) varieties
averaged 0.700 T/A increase per 1% kernel moisture drop (ranging from 0.225 to
1.011 T/A over 2 seasons and 7 varieties).
Percent cut-off increased approximately 1.04% for normal and se sweet
corn and 2.03% for sh2 supersweets per 1% drop in kernel moisture, depending
on season and cultivar (ranging from 0.04% to 1.85% for normal and sugary-
extender varieties to 1.12% to 3.38% for sh2 superweets).
Self-propelled and tractor-pulled harvesters are available from several
manufacturers. These come in single-row or multiple-row units of up to 8
rows. For fresh market corn harvest some of the harvesters have to be
slightly modified so that they do not damage the butt portion of the ear.
These modifications are generally easily made, and usually offered as options
from the manufacturer.
Baby corn has to be hand picked at, or within 1-2 days after silks
emerge from the ear tip. Feed corn varieties are harvested at silking, while
supersweet varieties may be harvested up to the time silks are about 2 inches
long but still fresh. Determine suitability of ears for picking by sampling
for size. Market requirements limit size to 4.5-10 cm. in length and 7-17 mm.
in diameter. Ears quickly become too long and tough. Carefully remove and
husk the ear so as not to break or damage it. For the fresh market, ears are
generally sold unhusked. They are very perishable and must be kept crisp.
Refrigerate to protect sugar levels that are important in baby corn flavor
quality. Ears intended for processing must be carefully hand husked and
de-silked. Process immediately by pickling or canning.
Popcorn: Mechanically harvested popcorn should be harvested when
kernels are between 16% and 18% moisture. If hand harvested, mositure may be
as high as 30% provided ears can be dried quickly to the necessary storage
moisture of 13.5% to 14.5%. In commercial production, mechanical handling
and moisture control are strictly controlled to maintain popping volume and
quality. Generally, popped corn that is "chewy" is too high in moisture,
while that leaving too many unpopped kernels is probably too dry and should be
conditioned. Other factors, especially mechanical damage can affect popping
quality.
STORAGE (Quoted from USDA Ag. Handbook #66):
Hold sweet corn at 32 F and 95 to 98 % relative humidity. Sweet corn is
seldom stored, although occasionally it may be desirable to store an excess
supply temporarily. However, storage for more than a few days results in
serious deterioration and loss of tenderness and sweetness. The sugar
content, which so largely determines quality in corn and which decreases
rapidly at ordinary temperatures, decreases less rapidly if the corn is kept
at about 32 F. The loss of sugar is about four times as rapid at 50 F as at
32 F. At 85 F, 60 % of the sugars may be converted to starch in a single day
as compared with only 6 % at 32 F. However, corn loses sweetness or desirable
flavor fairly rapidly, even when iced and held at 32 F. Long shanks and flag
leaves should be trimmed before marketing, as they induce denting of the
kernels by drawing moisture from them. Denting is an indication of loss of
quality. A loss of 2 % moisture from sweet corn may result in objectionable
kernel denting.
Rapid removal of field heat from sweet corn, when at 86 F or higher, is
especially critical to retard deterioration. Maximum quality retention can be
obtained by precooling corn to near 32 F with an hour after harvest and
holding ears at 32 F during marketing. In practice cooling to this extent is
rarely achieved. However, cooling is the first step in a good temperature
management program. Sweet corn has a high respiration rate, which results in
a high rate of heat evolution.
Sweet corn can be precooled adequately by vacuum cooling, but it must be
wetted first ( and top iced after vacuum cooling). Crated corn can be vacuum
cooled from about 85 F to 40 F in a half hour. Hydrocooling by spraying,
showering, or immersion in water at 32 to 38 F is effective, although it takes
longer than vacuum cooling for the same temperature reduction if the corn is
packed before it is cooled.
Crated corn would take over an hour in a hydrocooler to cool to 40 F,
and few if any, operators leave it that long. It is important to check cob
temperatures during hydrocooling to determine if temperatures are being
lowered to at least 50 F. Hydrocooling nomographs for bulk and crated sweet
corn are available. Many hydrocoolers now handle palletized crates, with
crates four or five layers high. These coolers, with overhead spray nozzles,
can be effective if they use a large volume of water and allow an hour or more
of operation. After hydrocooling, to icing is desirable during transport or
holding to hasten continued cooling, remove the heat of respiration, and keep
the husks fresh. When precooling facilities are not available, corn can be
cooled with package ice and top ice.
Sweet corn should not be handled in bulk unless copiously iced, because
it tends to heat throughout the pile. Corn should not be expected to keep in
marketable condition even in cold storage at 32 F for more than 5 to 8 days.
The storage life at 40 F is about 3 to 5 days and at 50 F about 2 days.
Some corn is prepackaged in moisture-retentive film, with the husks re-
moved after precooling. The film should be perforated to prevent development
of off-odors or off-flavors. This product is very perishable and must be
marketed with continuous refrigeration.
Use of controlled atmospheres to extend storage offers little promise.
Research has shown that injurious atmospheres contain less than 2 % oxygen or
more than 20 % carbon dioxide. In an atmosphere with 2 % oxygen, the sucrose
content of sweet corn remained higher than in other atmospheres tested.
Some of the new, high-sugar sweet corn cultivars should improve consumer
satisfaction. As compared with standard cultivars, which contain 3 to 5 %
sugar at harvest, the new cultivars contain 7 to 10 % sugar and also lose
their sweetness more slowly during marketing. Thus, consumers purchasing the
sweeter cultivars after several days' storage should get corn with 5 to 6 %
sugar as compared with standard cultivars containing only 2 to 3 % sugar after
similar post-harvest handling.
PACKAGING
Wirebound crates, 42-50 pounds, are commonly used as containers for
corn. Corn is packed 4 or 5 dozen per crate.
ENTERPRISE BUDGET
The following summary information has been taken from the sweet corn
enterprise budget for corn grown for processing, developed in 1993 by Bob
Lisec, Dan Mc Grath, and Tim Cross, Oregon State University Extension Service:
The sweet corn budget estimates total variable costs of $357.14 per acre and
total fixed costs of $217.81 per acre, resulting in $574.96 per acre to total
cost of production. The break-even price needed to cover variable costs is
$39.68 per ton, and the break-even price needed to cover all costs is $63.88
per ton, based on a normal yield of 9 tons per acre. For the complete budget
and assumptions used contact one of the above-mentioned authors.
PEST CONTROL FOR SWEET CORN
THE PESTICIDES LISTED BELOW, TAKEN FROM THE PACIFIC NORTHWEST PEST
CONTROL HANDBOOKS, ARE FOR INFORMATION ONLY, AND ARE REVISED ONLY ANNUALLY.
BECAUSE OF CONSTANTLY CHANGING LABELS, LAWS, AND REGULATIONS, OREGON STATE
UNIVERSITY CAN ASSUME NO LIABILITY FOR THE CONSEQUENCES OF USE OF CHEMICALS
SUGGESTED HERE. IN ALL CASES, READ AND FOLLOW THE DIRECTIONS AND PRECAUTION-
ARY STATEMENTS ON THE SPECIFIC PESTICIDE PRODUCT LABEL.
USE PESTICIDES SAFELY!
Wear protective clothing and safety devices as recommended on the label.
Bathe or shower after each use.
Read the pesticide label--even if you've used the pesticide before. Follow
closely the instructions on the label (and any other directions you have).
Be cautious when you apply pesticides. Know your legal responsibility as a
pesticide applicator. You may be liable for injury or damage resulting from
pesticide use.
WEED CONTROL
Cultivate as often as necessary when weeds are small. Proper cultiva-
tion, field selection and rotations can reduce or eliminate the need for
chemical weed control.
THE WEED TREATMENTS LISTED BELOW ARE TAKEN FROM THE PACIFIC NORTHWEST
WEED CONTROL HANDBOOK, AND ARE FOR INFORMATION ONLY. CONSULT PRODUCT LABELS
FOR CURRENTLY LEGAL REGISTRATIONS, RATES, AND COMPLETE INSTRUCTIONS.
WEED MANAGEMENT GENERAL STRATEGY
Sweet corn populations and row spacings represent compromises between
maintaining cob size, suppressing weeds, and utilizing existing equip-
ment. Thus, growers rotate crops for proso millet and perennial weed sup-
pression while depending on one or more herbicides for early and mid-
season weed control. Cultivation is optional depending on herbicides
employed, soil types, depth regulations, and irrigation.
______________________________________________________________________________
STALE SEEDBEDS FOR VEGETABLE PRODUCTION
Stale seedbeds are sometimes used for vegetable production when other selec-
tive weed control practices are limited or unavailable. The concept depends
on controlling the first flush of emerged weeds before planting or emergence
of the crop followed by minimal soil disturbance which reduces subsequent weed
flushes during establishment of the crop. Following establishment, other weed
control practices including cultivation or use of other herbicides can be
used.
1. Prepare a seedbed, preferably 2 to 3 weeks before planting to achieve
maximum weed seed germination near the soil surface. Soil temperatures
and moisture must be reasonable or results will be erratic.
2. Plant the crop with minimum soil disturbance. Otherwise, new weed seed
will be exposed to favorable germinating conditions.
3. Just before or after planting but before crop emergence, treat the
field by flaming or with herbicide to kill all germinated or exposed
weeds.
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
Flaming
Use liquid propane or similar fuel-burning equipment to quickly sear the
weeds, but not consume them with flame.
------------------------------------------------------------------------
paraquat 0.625 to 0.94 lb ai/A
Gramoxone Extra
Restricted-use pesticide. Do not ingest or inhale spray mist. Wearing
protective face shields, respirators, and clothing is advised. Apply
during or after planting, but before crop emergence. Add a nonionic
surfactant or crop oil concentrate according to label specifications,
taking care to avoid anionic formulations that react in the tank to form
insoluble precipitates. Exposed crop plants will be killed. Do not
apply preplant or preemergence to soils lacking clay minerals, such as
peat, muck, pure sand, or artificial planting media. (Acts as contact;
absorbs energy produced by photosynthesis forming peroxides that disrupt
living cells.)
------------------------------------------------------------------------
glyphosate Consult Labels
Roundup
Roundup RT
(E. Washington and
Idaho only)
or Honcho + nonionic surfactant
Apply to actively growing weeds either preplant in conjunction with site
preparation or preemergence crops listed on the label. Consult label
for specific rates, times of application, and perennial species control-
led. Generally 1 to 1.5 lbs ai/A should be used for annual weeds, while
perennial weeds require higher rates. Addition of a surfactant or
ammonium sulfate improves activity when weeds are stressed. Do not
apply more than 8 lbs. ai/A per year, nor plant non-labeled crops within
12 months following application. (Inhibits production of 3 amino acids
and protein synthesis.)
______________________________________________________________________________
PREPLANT INCORPORATED
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
butylate + 4 to 6 lb ai/A
safener
Sutan
(not for seed stock)
Apply preplant to soil dry enough for thorough mixing and incorporate
immediately by disking in 2 directions or rototilling into top 2 to 3
inches of soil. Avoid planting corn seed more than 2 inches deep.
Suppresses growth of yellow nutsedge and other perennial grasses.
Consult label regarding other tank-mixes. Injury may occur if crop
grows under adverse conditions such as extended cold/wet or hot/dry
periods or pest attacks. (Inhibits shoot growth).
------------------------------------------------------------------------
EPTC + safener 3.12 to 6.14 lb ai/A
Eradicane
Apply preplant to soil dry enough for thorough mixing and incorporate
immediately by disking in 2 directions or rototilling into top 2 to
3 inches of soil. Avoid planting corn seed more than 2 inches deep.
Suppresses growth of yellow nutsedge and other perennial grasses.
Consult label regarding other tank-mixes. Injury may occur if crop
grows under adverse conditions such as extended cold/wet or hot/dry
periods or pest attacks. (Inhibits shoot growth).
------------------------------------------------------------------------
cyanazine Consult label
Bladex
A restricted-use herbicide. Note crop restrictions and information in
Preemergence Soil-Applied section below. Incorporate in top 2 in. of
soil.
______________________________________________________________________________
PREEMERGENCE SOIL-APPLIED
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
alachlor 2 to 4 lb ai/A
Lasso, Partner
Apply immediately before planting and incorporate mechanically in top 1
to 2 inches of soil for furrow-irrigated corn or apply after planting
and incorporate to depth of moisture by cross spike-tooth harrowing or
activate with overhead irrigation. Can be applied through a center
pivot irrigation system. Consult label for specific rates depending on
soil texture, organic matter, and possible use of tank-mixes or other
herbicide combinations. Controls atrazine resistant redroot pigweed,
nightshade, and purslane. (Inhibits roots and shoots).
------------------------------------------------------------------------
metolachlor 1.5 to 3.0 lb ai/A
Dual
Apply preplant, preemergence, or early postemergence before weeds begin
to germinate or yellow nutsedge begins to emerge. Activate with
shallow incorporation or overhead moisture. If furrow irrigated, apply
preplant and incorporate mechanically in top 2 to 3 inches of soil.
Consult label for specific rates depending on soil texture and especial-
ly organic matter or for restrictions on planting sensitive crops within
4 to 5 months. (Inhibits roots and shoots).
------------------------------------------------------------------------
butylate + safener 4 to 6 lb ai/A
Sutan +
(not for seed stock)
In semi-arid regions of Eastern Oregon, Eastern Washington, and Idaho,
may be surface applied immediately after planting to dry soil (at least
0.5 inch deep) that remains free of dew and incidental moisture and
incorporated with overhead irrigation within 36 hours. Note other
remarks and limitations described above.
------------------------------------------------------------------------
atrazine 1.6 to 2.4 lb ai/A
several brands
A restricted-use herbicide. Apply preplant or preemergence by selecting
rates depending on soil type listed on the label. Activate with over-
head irrigation within 7 days or incorporate mechanically in top 2
inches of soil for rill irrigated fields east of the Cascades. Poor
control of barnyardgrass and yellow foxtail will result if the soil
surface remains dry or these grasses grow beyond the 2-leaf stage.
Quackgrass can be controlled with 4 lb applied once or a split
application of 2 lb. Avoid planting crops other than corn during the
season of treatment. Other crops can be planted the following year
west of the Cascades if treated before June 10 with 2 lb or less per
acre; east of the Cascades, corn should be planted using other herbi-
cides the following year. Often, tank-mixes or applications of herbi-
cides will improve control of resistant weeds. Do not graze treated
area or feed treated forage to livestock for 21 days following applica-
tion, nor apply more than 4 lb ai/A per year. Following harvest, plow
and thoroughly mix the soil to reduce possible injury. (Inhibits
photosynthesis).
------------------------------------------------------------------------
cyanazine Consult label
Bladex
A restricted-use herbicide. Note crop rotation restrictions stated on
the label. Apply either preplant incorporated (2 in. deep) or pre-
emergence and activate with rainfall, irrigation, or rotary hoeing
within 10 days. Select rates depending on soil type and organic matter
listed on label. Adjust ratios of cyanazine and atrazine depending on
expected grass or broadleaf infestation according to label directions.
Note restrictions for both products, especially sweet corn cultivars,
crop rotations, and feeding of livestock. Other tank-mixes are la-
belled. (Inhibits photosynethesis.)
______________________________________________________________________________
POSTEMERGENCE SOIL AND/OR FOLIAR-APPLIED
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
atrazine with 1 to 2 lb ai/A
crop oil +
1 gal crop oil
A restricted-use herbicide. Apply postemergence before grass weeds
exceed 1.5 in. and broadleaf weeds 4 to 6 in., but before corn is 20 to
30 inches tall. Use lower water carrier volumes to improve activity.
Do not exceed 1 to 1.5 lb ai/A when wheat is expected to follow in the
rotation. Consult label for replanting sensitive crops within 12 to 24
months. Do not apply more than 1 time per season except as suggested to
suppress yellow nutsedge and Canada thistle. Reduce potential residues
in soil by avoiding applications exceeding 2 lb or select other herbi-
cides. (Inhibits photosynthesis).
------------------------------------------------------------------------
bentazon 0.75 to 1.0 lb ai/A
Basagran
Apply to small annual broadleaf weeds (see label for maximum weed size).
Use higher rate with crop oil concentrate applied 2 times, 7 to 10 days
apart for Canada thistle and yellow nutsedge. Irrigate before applica-
tion to ensure vigorous weed growth. Poor control is achieved when day
and night temperatures are below 75 F and 55 F. Use a minimum of 5 gal
water per acre and at least 40 psi to ensure thorough coverage of weed
foliage. Temporary leaf speckling may occur, but plants continue growth
without further symptoms within 10 days. Do not apply to corn growing
under stress conditions, nor mix with other pesticides. Do not apply
more than 2 lb ai/A per season. (Inhibits photosynthesis).
------------------------------------------------------------------------
bentazon 2.0 to 3.5 pts.
+ product/A
atrazine
Laddok
Atrazine is a restricted-use herbicide. Use only in Western Oregon and
Washington. Apply early postemergence when weeds are small and actively
growing. Adjust rates depending on weed size listed on label. Controls
broadleaf weeds. Note limitations for atrazine and bentazon above.
(Inhibits photosynthesis.
------------------------------------------------------------------------
amethryn 1.6 to 2.0 lb ai/A
Evik
Apply as a postemergence directed spray aimed downward or across base of
corn plant. Wild proso millet control requires early season sup-
pression using a preplant or preemergence treatment that achieves a
growth differential between the weed and crop. Selectivity is achieved
by accurate placement below actively growing corn leaves using drop
nozzles, gauge wheels, and leaf lifters to protect corn. Add a
surfactant (0.5% of spray volume) in a minimum of 20 gal water/A to
ensure thorough coverage. Do not spray over top of corn or within 3
weeks of tasseling. Consider grain rotations planted in the fall after
treatment, but do not plant other crops until the following year.
Grazing is possible after 30 days. (Inhibits photosynthesis; acts like
contact.)
------------------------------------------------------------------------
2,4-D 0.5 to 0.75 lb acid equivalent/A
amine,
oil-soluble amine,
or diamine acid
Apply after corn is tall enough for use of drop nozzles between rows.
Use the same precaution in spraying 2,4-D as suggested under winter
cereals to avoid drift injury. Avoid contact with corn foliage to
reduce brittle stalks and whorl distortion that prevents tassel
emergence. Do not apply from tasseling to dough stage of corn. Crop
injury is more likely to occur if corn is growing rapidly under high
temperature and high soil moisture. (Mimics natural plant hormones).
------------------------------------------------------------------------
paraquat 0.25 to 12.8 fl oz/A
Gramoxone Extra
A restricted-use pesticide. Do not ingest or inhale spray mist.
Wearing protective face shields, respirators, and clothing is advised.
Apply postemergence as a directed spray when corn is at least 10 inches
tall with nozzles arranged to spray no higher than the lower 3 inches
of corn stalks. Add a nonionic surfactant or crop oil concentrate
according to label specifications, taking care to avoid anionic formula-
tions that react in the tank to form insoluble precipitates. Acts as
contact; absorbs energy produced by photosynthesis forming peroxides
that disrupt living cells.)
------------------------------------------------------------------------
sethoxydim 0.19 lb ai/A
Poast
Apply as a postemergence directed spary aimed downward or across base of
corn plant. Corn must be greater than 30 inches tall and treatments
must not exceed 10 inches on the corn stalk. Drop nozzles, shields,
leaf lifters, and gauge wheels will reduce potential injury. Also corn
varieties that tiller profusely may be injured. (Inhibits fatty acid
production, cell membranes, and new growth).
______________________________________________________________________________
QUACKGRASS AND OTHER PERENNIAL GRASS CONTROL
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
glyphosate Consult Labels
Roundup or
Honcho +
nonionic surfactant
Spot treat vigorously growing quackgrass patches when 6 to 8 inches tall
by eliminating both the weed and crop within the treated area. Spray
before silking of corn to avoid residues in the harvested crop. Do not
treat more than 10% of the acreage. (Inhibits production of 3 amino
acids and protein synthesis).
------------------------------------------------------------------------
EPTC,
butylate
See Corn Preplant Incorporated section. (Suppresses perennial grass
growth only).
------------------------------------------------------------------------
atrazine 2 to 4 lb ai/A
A restricted use herbicide. Apply in fall or preferably spring, either
as a single application at higher rates 1 to 3 weeks before plowing to
actively growing quackgrass foliage or as a split treatment with the
first application before plowing and the second application before,
during, or after planting before weeds are 1.5 inches tall. Addition of
a nonionic adjuvant will enhance control. Wild proso millet control is
poor. Consult label for planting sensitive crops within 12 to 24 months
depending on time of applica- tion and total amount applied. Select
other herbicides with reduced soil persistence to reduce carryover. Do
not graze treated area or feed treated foliage to livestock for 21 days
following treatment. (Inhibits photosynthesis).
______________________________________________________________________________
WILD PROSO MILLET CONTROL
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
Biology and management
Wild proso millet mimics sweet corn growth. Seeds mature before corn
harvest, thereby facilitating spread with machinery. Seed longevity in
soil, however, is relatively short maybe 3 to 5 years. Control strate-
gies include crop rotation involving short-cycle or broadleaf crops,
narrow row spacings (20 inches in midwest), late planting dates, and
combinations of pre-and postemergence herbicides combined with appropri-
ate application equipment. Postemergence herbicide applications depend
on a height differential between corn and wild proso millet. Early
season millet suppression or control is essential with nitrogen manage-
ment, preemergence herbicides, and cultivation. (Reduce seed bank,
improve crop competition, and delay early growth for proper placement of
a non-selective postemergence herbicide.)
------------------------------------------------------------------------
metolachlor
See Preemergence Soil-Applied section. (midwest evidence suggests
slightly less effective than herbicides such as vernolate.)
------------------------------------------------------------------------
ametryne
See Postemergence Soil and/or Foliar-Applied section.
------------------------------------------------------------------------
paraquat
See Postemergence Soil and/or Foliar-Applied section.
______________________________________________________________________________
YELLOW NUTSEDGE CONTROL
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
EPTC,
butylate
See Corn Preplant Incorporated section. (Suppresses yellow nutsedge
emergence, but does not kill nutsedge tubers.)
------------------------------------------------------------------------
metolachlor
See Corn Preemergence Soil-Applied section. (Applications inhibit new
tuber formation and reduce infestations.
------------------------------------------------------------------------
bentazon
See Corn Postemergence section. (Controls tubers in Oregon with split
treatments applied under warm weather conditions).
------------------------------------------------------------------------
atrazine 2 to 4 lb ai/A
A restricted-use herbicide. Apply either single or split applications
according to one of 6 alternative control methods listed on label.
Yearly applications or use of other herbicides can reduce populations if
few plants survive the growing season. Consult label for planting
sensitive crops within 12 to 24 months depending on time of application
and total amount applied. (Inhibits photosynthesis).
______________________________________________________________________________
Canada Thistle Control
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
bentazon
See Corn Postemergence section.
------------------------------------------------------------------------
2,4-D
See Corn Postemergence section.
------------------------------------------------------------------------
glyphosate Consult Labels
Roundup or
Honcho +
nonionic
surfactant
Apply at late bud to early bloom stage of thistle, but before silking of
corn. Spot spray thistle patches eliminating both the weed and crop
within the treated area. Spray before silking of corn to avoid residues
in the harvested crop. Do not treat over 10% of the acreage. (Inhibits
production of 3 amino acids and protein synthesis).
______________________________________________________________________________
______________________________________________________________________________
INSECT CONTROL
Proper rotations and field selection can minimize problems with insects.
THE PESTICIDES LISTED BELOW ARE TAKEN FROM THE PACIFIC NORTHWEST INSECT
CONTROL HANDBOOK, AND ARE FOR INFORMATION ONLY. CONSULT PRODUCT LABELS FOR
CURRENTLY LEGAL REGISTRATIONS, RATES AND COMPLETE INSTRUCTIONS.
Insect and Description Control, Active Ingredient Per Acre
---------------------------------------------------------------------------
Aphids Lorsban 4E - 0.5 to 1.0 lb
Several species
Metasystox-R - 0.5 lb
Plant lice. Suck sap, may be-
come very abundant on leaves, endosulfan - 1 lb
especially in eastern Oregon. Do not feed treated forage.
For fresh market use only.
WARNING: Microencapsulated methyl
parathion (Penncap-M) should never Phosdrin - 0.5 lb
be sprayed on pollen-shedding corn,
including adjacent fields and malathion - 1 lb
blooming weeds in field edges or
adjacent fields. If misused, Penncap-M - 0.5 to 0.75 lb
this formulation is especially
hazardous to honey bees and other Asana - 0.03 to 0.05 lb
pollinating insects because of
its strong tendency to contaminate Di-Syston - 1 lb
pollen.
---------------------------------------------------------------------------
Corn earworm carbaryl - 1 to 2 lb
Heliothis zea
WARNING: Carbaryl dust should
Large, green, brownish or red- never be applied to pollen-
dish worms that feed on silk shedding corn because of severe
and kernels of the ear. hazard to pollinating bees.
Lannate - 0.45 lb
Asana - 0.025 to 0.05 lb
Penncap-M - 0.5 to 1.0 lb
WARNING: Microencapsulated
methyl parathion (Penncap-M)
should never be sprayed on
pollen-shedding corn, including
adjacent fields, and blooming
weeds in field edges or
adjacent fields. If misused,
this formulation is especially
hazardous to honey bees and
other pollinating insects
because of its strong ten-
dency to contaminate pollen.
permethrin - 0.1 to 0.2 lb
Lorsban 4E - 0.75 to 1.0 lb
---------------------------------------------------------------------------
Corn rootworms phorate - 1.2 oz ai/1000 row
Diabrotica spp/in part ft.
Larvae feed on roots of corn Counter 15G - 1.2 oz ai/1000
causing stunting, lodging, and row ft.
occasional death of plants.
Larvae are inch long, white Dyfonate - 0.75 to 4 lb
with brown-yellow heads. Only
an occasional, primarily loca- Lorsban 15G - 0.075 lb ai/1000
lized problem on field corn row ft.
grown in the north coast re-
gions and portions of Idaho. Lorsban 4E - 3 lb
Furadan - 1.2 oz ai/1000 row
ft.
Mocap - 0.075 lb ai/1000 row
ft.
diazinon - 0.04 to 0.078 lb per
1000 row ft.
Di-Syston - 0.075 lb ai per
1000 row ft.
Holdem - 6 to 10 oz product/1,000
row ft. (ethoprop + phorate)
---------------------------------------------------------------------------
Corn rootworm: Adults including To control adult beetles use:
Diabrotica undecimpunctata
methoxychlor - 1 to 2 lb
Yellowish-green, black-spotted
beetle. Sometimes feed on new Diazinon - 1 to 1.25 lb
silks causing unfilled ears. Highly toxic to bees.
Observations indicate noticeable
damage occurs when populations Asana - 0.025 to 0.05 lb
reach 2 per ear.
permethrin - 0.1 to 0.2 lb
Lorsban 4E - 0.5 to 1 lb
Lannate - 0.225 to 0.45 lb
malathion - 0.94 lb
carbaryl - 1 to 2 lb
---------------------------------------------------------------------------
Cutworms and Armyworms Lorsban 4E - 1 to 2 lb preplant
Various spp. for cutworms. 1.0 to 1.5 lb
postemergence for cut-
Reddish, green, or black worms. worms and 0.5 to 1 lb for
Tunnel into base of plant, cut armyworms.
off seedlings or feed on foliage.
Lorsban 15 G - 1 to 2 lb pre-
plant - 0.075 to .15 lb ai/
1000 row ft. at planting.
Cutworms only.
Asana - 0.025 to 0.05 lb
trichlorfon - 0.5 to 1 lb
carbaryl bait - 2 lb
Lannate - 0.45 lb
Fall armyworm only.
methoxychlor - 2.25 lb
Armyworm only
Bacillus thuringiensis - 1 to 2
qt. Use a spreader-sticker to
enhance control.
permethrin - 0.1 to 0.2 lb
Mocap - 0.075 lb ai/1000
row ft. Black cutworm only.
diazinon - 2 to 4 lb
Cutworms only.
malathion - 0.94 to 1.25 lb
Armyworms only.
Dyfonate 4E - 4 lb
Black cutworm only.
Penncap-M - 0.5 to 0.75 lb for
armyworms. l.0 lb for black
cutworm.
WARNING: Microencapsulated
methyl parathion (Penncap-M)
should never be sprayed on
pollen-shedding corn, including
adjacent fields, and blooming
weeds in field edges or
adjacent fields. If misused,
this formulation is especially
hazardous to honey bees and
other pollinating insects
because of its strong ten-
dency to contaminate pollen.
Furadan 15G - 1.2 oz ai/1000
row ft.
Holdem - 10 oz product/1,000
row ft. (ethoprop + phorate)
---------------------------------------------------------------------------
Western bean cutworm carbaryl - 2 lb
Loxagrotis albicosta
Asana - 0.0125 to 0.025 lb
Large, brown larvae that enter
ears at any point and feed on permethrin - 0.1 to 0.2 lb
kernels.
Lorsban 4E - 1 to 1.5 lb
---------------------------------------------------------------------------
Garden Symphylan Mocap - .075 lb ai/1,000 row ft
Scutigerella immaculata
Lorsban 15G - 0.075 to 0.1 lb
Small, white, centipede-like ani- ai/1000 row ft.
mals in soil.
Lorsban 4E - 1 to 2 lb
Dyfonate 4E, 10G or 20G - 2 lb
diazinon - 10 lb
Telone II or C-17 - preplant
Holdem - 10 oz product/1,000
row ft (ethoprop + phorate)
---------------------------------------------------------------------------
Grasshopper malathion - 1.0 lb as spray
Several spp.
carbaryl - 0.5 to 1.5 lb
May cause considerable marginal
damage in years of grasshopper Lorsban 4E - 0.25 to 0.5 lb
abundance.
Asana - 0.025 to 0.05 lb
methyl parathion - 0.5 lb
diazinon- 0.5 lb
Furadan - 0.125 to 0.25 lb
Penncap-M - 0.25 to 0.75 lb
WARNING: Microencapsulated
methyl parathion (Penncap-M)
should never be sprayed on
pollen-shedding corn, including
adjacent fields, and blooming
weeds in field edges or
adjacent fields. If misused,
this formulation is especially
hazardous to honey bees and
other pollinating insects
because of its strong ten-
dency to contaminate pollen.
---------------------------------------------------------------------------
Slugs metaldehyde baits
---------------------------------------------------------------------------
Seedcorn maggot Seed Treatment
Delia platura Lorsban 50SC - 1 oz ai/100
lb of seed
White larvae of a fly. Attack
germinating seeds and may Soil Treatments
destroy planting. Damage
most serious during cool, wet Counter 15G - 1.2 oz ai/1000
weather. row ft.
Thimet 20G - 1.2 oz ai/1000
row ft.
Dyfonate 10G or 20G - 4 lb
Lorsban 15 G - 0.075 lb ai/
1000 row ft.
Lorsban 4E - 2 lb
diazinon 50W - .25 lb ai/bu
Furadan - 1.2 oz ai/1,000 lin
ft of row at planting
Germate Plus - 1.8 oz of
formulation/50 lb seed.
Planter box treatment.
Holdem - 1 to 8 oz. product/
1,000 row ft. (ethoprop + phorate)
---------------------------------------------------------------------------
Spider mites Metasystox-R - 0.5 lb
Tiny, spiderlike animals lo- Di-Syston E - 0.5 to 1.0 lb
cated on underside of leaves.
Cause yellowing or silvering of Di-Syston 15 G - 1 lb
leaves. Feed on plant juices
and may contribute to early Thimet 20G - 1.2 oz ai/1000
maturity and poor quality of row ft.
corn.
Comite - 1.6 to 2.4 lb
---------------------------------------------------------------------------
Thrips Metasystox-R - 0.375 to 0.5 lb
probably Frankliniella
malathion - 1 lb
Small yellowish insects about
1/25 inch long. Rasp young Di-Syston EC - 1 lb
tender leaves of small seedling
plants. Treatment rarely justi- Di-Syston 15G - 1 lb
fied and only then on very small
plants under water stress.
---------------------------------------------------------------------------
Wireworms Dasanit - 0.5 to 1 lb
Ctenicera and
Limonius spp. diazinon - 3 to 4 lb
Brown, jointed larvae of click Dyfonate - 4 lb
beetles. Kill young plants,
weaken older ones. Lorsban 15G - 2 lb preplant
or 0.075 to 0.15 lb ai/1000
row ft.
Lorsban 4E - 2 lb
Counter 15G - 1.2 to 2.4 oz
ai/1000 row ft.
Furadan 15G - 1.2 oz ai/1000
row ft.
Mocap - 0.075 lb ai/1000 row
ft.
Telone II or C-17 Preplant.
Germate Plus - 1.8 oz of
formulation/50 lb seed.
Planter box treatment.
Holdem - 6 to 8 oz product/
1,000 row ft (ethoprop + phorate)
___________________________________________________________________________
___________________________________________________________________________
DISEASE CONTROL
Proper rotations, field selection, sanitation, spacings, fertilizer and
irrigation practices can reduce the risk of many diseases. Fields can be
tested for presence of harmful nematodes. Using seed from reputable seed
sources reduces risk from seed born diseases.
THE PESTICIDES LISTED BELOW ARE TAKEN FROM THE PACIFIC NORTHWEST DISEASE
CONTROL HANDBOOK, AND ARE FOR INFORMATION ONLY. CONSULT PRODUCT LABELS FOR
CURRENTLY LEGAL REGISTRATIONS, RATES AND COMPLETE INSTRUCTIONS.
SWEET CORN -- BACTERIAL SOFT ROT
Cause: Erwinia sp.
Symptoms: Soft rot of the stalk at nodes and where base of leaf joins the
stalk. Severe losses have occurred in Oregon and Washington plantings in
recent years. Collection of moisture at the base of the leaf from overhead
irrigation, especially if nitrogen is applied by over-head irrigation, or
heavy dews, is believed to be one of the contributing factors. In Oregon, the
disease is usually more severe when stagnant water is used for irrigation. Use
well water if possible. Observations in Washington indicate that the disease
is frequently severe in plantings grown in sulfur-deficient soils. The variety
`Jubilee' is very susceptible to the disease.
~Control:
1. Furrow irrigate if possible.
2. Suggest for trial, applications of copper-containing fungicides to protect
the stalk, nodes, and leaf sheaths.
---------------------------------------------------------------------------
CORN -- MAIZE DWARF MOSAIC
Cause: A virus. The disease was first found in Ohio in 1962 and was not known
to occur in the Pacific Northwest until 1977 when losses in sweet corn
occurred in the Twin Falls area. Severe losses have occurred most years since
1962 in most of the major corn-producing states east of the Rocky Mountains
and in California.
Symptoms: Initial symptoms appear as small chlorotic spots and streaks
generally concentrated in the lower one-third of the newly forming leaves in
the whorl of the plant. These spots and streaks may coalesce to form light
green or yellow mosaic patterns on the leaves. Stunting may or may not be
present. The mosaic symptoms may increase in extent and intensity over time,
but frequently decrease in intensity later in the season making identification
based on leaf symptoms difficult or of questionable accuracy. Where stunting
occurs, plants may be only one-third to one-half as tall as healthy plants.
Infected plants may be barren or, where ears are formed, seed fill may be
spotty and incomplete.
Maize dwarf virus is transmitted in nature by aphids and can infect sorghum,
Johnson grass, yellow foxtail, crabgrass, and other wild grasses. Strains
differ in host range. Strain B cannot be transmitted to Johnson grass.
Symptoms may appear in as little as 5 days after infection. Usually infections
have been found where Johnson grass is in close proximity.
~Control: Early seeded sweet corn may escape aphid flights. Varieties of sweet
corn vary in tolerance. Some are tolerant at some locations but not at others.
More information is needed on virus-strain, variety interaction before
varietal recommendations can be made.
---------------------------------------------------------------------------
SWEET CORN -- ROOT, STALK, AND EAR ROT
Cause: Several fungus organisms which overwinter on corn crop residue, in the
soil, or are carried on the seed. Incidence of the root and stalk rot phase is
associated with moisture stress and overfertilization with nitrogen.
Symptoms: Brown decayed spots appear on the roots, and the disease moves into
the crown. Root rot is usually, but not always, accompanied by stalk or ear
rot. Root and stalk rot causes premature dying and the rotted stalks break
over as the crop matures. Ear rot may be recognized by white, gray, pinkish,
or dark fungus growth over the kernels.
~Control: Use disease-free seed chemically treated with Arasan or captan. Crop
rotation and clean plowing, or removal of dead corn stalks and leaves, reduces
the amount of disease. Do not overfertilize with nitrogen. Avoid root pruning
when closely cultivating, and injecting fertilizer.
---------------------------------------------------------------------------
CORN -- SEED ROT AND SEEDLING BLIGHT
Cause: Several fungus organisms which overwinter on corn crop residue, in the
soil, or are carried on the seed.
Symptoms: In the cold soils, seeds decay or seedlings die before they emerge.
In warmer soils, seedlings usually emerge but are stunted and have brown,
rotted roots and crowns.
~Control: Seed treatment with Thiram, Vitavax, or captan. Select planting sites
and dates to take advantage of warm soils. Crop rotation and destroying old
corn stalks is helpful.
---------------------------------------------------------------------------
CORN -- SEED TREATMENT
Aids in control of seed decay and damping-off.
Sweet corn--1.5 oz dry, 4.0 oz slurry actual/100 lb. Considered to be a
nonfood use.
Where Pythium is a problem, apply Apron 25W at 4 to 14 oz/cwt of seed or
Anchor flowable at 0.75 to 1.5 oz/cwt of seed.
Baytan 30 F (commercial seed treaters only) use 3 fl oz product/cwt seed for
head smut (Sphaelotheca reiliana).
Captan 75 Seed Protectant 2 oz/bushel. Considered to be a nonfood use.
Vitavax 200--37.5 percent Vitavax 37.5 percent thiram use 4 oz of the prod-
uct/100 lb of seed. This formulation is preferred to other Vitavax formula-
tions.
Vitavax 34 percent flowable use 2 to 4 fl oz/100 lb seed.
Vitavax 25-DB use 4 to 6 oz/100 lb seed.
Vitavax + thiram--4 oz of formulation of 37.5 percent Vitavax and 37.4 percent
thiram/100 lb of seed. Vitavax tolerance 0.2 ppm. Thiram-- considered to be a
nonfood use.
---------------------------------------------------------------------------
CORN -- SMUT (Common)
Cause: Ustilago maydis, a fungus which overwinters as spores. It is possible
that the spores may survive 2 or 3 years. When corn stalks have been fed to
cattle, the spores are carried in the manure. Spores may be windblown long
distances.
In the Pacific Northwest the fungus attacks only the corn plant. The younger
the plant the more susceptible it seems to be. After the ears have formed, it
becomes rather resistant. Any part of the plant above ground may become
infected, but the ear is most commonly affected. Infection is increased when
there is injury from hail, removal of tassels, earworm, or borers.
In the warm season the amount of smut present coincides closely with the
degree of moisture in the soil, especially during June. When temperatures are
lower than average, there may be little smut even though soil moisture is
high. Moist soil that has had applications of manure generally favors smut
infection.
Below 61 F there is little spore germination. Optimum for spore germination,
is 79 to 100 F.
`Jubilee', the most popular variety, is susceptible to smut.
Symptoms: A ball composed of a white smooth covering of corn tissue enclosing
a great mass, sometimes 4 or 5 inches in diameter, of black, greasy, or
powdery spores. The covering becomes dry and brittle, breaks open, and permits
the black powdery content to sift out. There is no stringy mass of vascular
tissue as in head smut.
~Control: Control measures are unsatisfactory. Planting tolerant varieties
offers the best control.
1. Seed treatment is of no value--the spores are not transmitted with the
corn seed.
2. The best hope seems to lie in developing an area or community control
program in which growers go through their fields two or three times a season
cutting out the smut balls before they break open. Such a program should be
carried on for 2 to 3 years. After the smut balls are removed, they should be
placed in a receptacle that will not permit the spores to spill out, then
burned or buried deeply.
---------------------------------------------------------------------------
CORN -- SMUT (Head)
Cause: Sphacelotheca reiliana, a fungus that survives as spores in the soil.
It is not known how long the spores will remain viable in the soil, but they
have been known to persist at least 5 to 7 years. Spores may be windblown long
distances.
The fungus has been observed only on corn in the Pacific Northwest however,
two strains of the fungus occur which can infect sorghum. There is only one
corn-infecting strain known at present.
Infection is reported to occur while the corn plant is in the seedling stage
however, greenhouse studies have demonstrated that infection can occur several
weeks after the corn has been planted. After infection, the fungus develops
systemically in the plant.
Infection may occur at soil temperatures as low as 59 F, but it occurs more
readily at higher soil temperatures (68 to 86 F). The fungus is not inter--
nally seedborne but can be carried on the surface of the seed.
Symptoms: The sporulating sites of the fungus occur in the tassel or ear and
on an occasional leaf. The sorus is coarse and on eruption reveals dry spore
masses with strands of vascular tissue. Infected plants often are dwarfed in
size. Dwarfing may be a dominant symptom in some varieties. The ears may be
aborted or mere rudiments with leaf buds instead of the normal ear. Usually
the entire ear is replaced by smut spores, but occasionally some will bear a
few kernels of corn. Tassel infection may be complete or partial. Infection
may be confined to individual spikelets or it may proliferate and cause
bizarre leafy structures. Some plants may have both the ear and tassel
infected with smut. In instances when only the ear is infected, the tassels
are sterile.
~Control: Rotation out of corn for 3 to 4 years is the best control measure.
Breeding for resistance has just been initiated. Varieties, however, differ in
susceptibility. Several varieties, `Style-pak' (Ferry-Morse), `Commander'
(Asgrow), `Rapidpak' and `Reliance' have shown resistance and are useful for
commercial plantings. Two other varieties, `Goldie' and `Blitz', are resis-
tant, but are useful only in home gardens because of other characteristics.
Cultural practices have been shown to reduce the incidence of smut. Planting
shallow (1 inch) to promote rapid germination, preplant irrigation, and keep-
ing the seed bed moist during the first 4 weeks after planting have reduced
head smut infection in plots at the Vegetable Crops Farm in Corvallis, Oregon.
Since we do not have adequate control measures at the present time, it would
be wise to restrict the spread of this disease. The most likely method of
spread within the Willamette Valley is corn pickers. When a picker has been
used in an infested field, it should be thoroughly decontaminated before
removing it from the field. The most practical method available is steam
cleaning. If steam cleaning equipment is not available, it should be thorough-
ly washed with soap and water, preferably under high pressure.
In fields containing a light infestation, rotating at least 2 years with crops
other than corn is suggested. It also is suggested that wherever possible
plant corn upwind of known infested fields.
Seed treatment with Baytan 30 F at 3 fl oz/cwt seed (commercial seed treaters
only) will reduce seedling infection.
______________________________________________________________________________
______________________________________________________________________________
---------------------------------------------------
---------------------------------------------------
This information was adapted by the Oregon State
University Extension Service from Oregon and
Pacific NW publications as well as other vegetable
production guidelines from public institutions
in the U.S. and Canada. These guidelines are
intended as a general guide for Oregon commercial
vegetable producers. Address comments or questions
to your County Extension Agent or Dr. N. S.
Mansour, Department of Horticulture, Oregon State
University, Corvallis, OR 9733l.
---------------------------------------------------
---------------------------------------------------