From: Brian Lo <dragon@csulb.edu>
Newsgroups: rec.gardens
Subject: FAQ: Onions
Date: Wed, 1 Mar 1995 14:55:54 -0800
ONIONS, DRY BULB, WEST OF THE CASCADES
Allium cepa
See separate files: Onions, Dry Bulb, East of the Cascades (ONIONB-E),
or: Onions for Dehydration (ONDHY), or: Onions - pearl, sets and boilers
(ONPRL), or: Green Bunching Onions (ONGRN).
Dry bulb onion in the Pacific Northwest may be classified into two
distinct catagories those that are grown on muck soils, and those grown on
mineral soil. By far, most are produced on mineral soils. Mineral soil
onions are produced in two different regions, west of the Cascade Mountains,
and east, notably in the Treasure Valley and the Columbia Basin. On both
sides of the Cascades, mineral soil onions may be spring-planted or fall-
planted for over-winter production. Over-winter production has been well
established in the Milton-Freewater area of Oregon and the Walla Walla area in
Washington. Over-winter production west of the Cascade Mountains is relative-
ly new, and restricted to the Willamette Valley. Over-winter onion production
is more risky, but allows harvest of onions in late May and June when onion
prices are historically the highest of the year.
Bulb onion varieties are classified according to day length. All bulb
onions grown in the Pacific Northwest are classified as long-day varieties
requiring 14 or more hours of day length before bulbing occurs. Technically,
all onions are "long-day" plants, in that bulbing begins as day length inc-
reases. Short-day varieties are those requiring only 10 to 12 hours of day
length for bulbing to occur. These are grown in southern states generally
below the 35 th. parallel, and are not suitable for bulb production in the
northwest, except as pearl or boiler varieties, or for over-winter production.
Temperatures and light intensity and quality (red:far red) can modify
onion bulbing response. High temperatures and bright days can "compensate"
for some day length, causing onions to bulb sooner than they would otherwise.
Overcast, cool temperatures, delay bulbing. Time of bulbing is an important
factor in determining onion bulb size. Early bulbing contributes to small
bulb size, with delayed bulbing resulting in larger size.
Uniformity of maturity (rate of tops-down) is very important in bulb
size uniformity and storage quality. Tops-down in hybrid varieties tends to
occur over a period of only a day or two, with close to 100% of the tops
falling. Non-uniform varieties may have tops falling over a period of several
weeks with a percentage of the tops not falling at harvest. In such variet-
ies, bulbs with early tops-down contribute to incidence of bald onions at
harvest, while those whose tops resist falling do not cure properly, contrib-
uting to decay in storage.
Cool temperatures, poor stands and late plantings predispose varieties
to bull necks, a trait that contributes to poor storability. This is espe-
cially true of late, varieties that may have poor bulbing uniformity qualities
(sometimes more prevalent in non-hybrids).
Selecting the correct variety for your production area and understanding
the climatic and other environmental factors that affect its performance is
extremely important.
VARIETIES
Western Oregon (spring seeded):
Muck soils; spring seeded, yellow: Simcoe, Sentenial, Capable, Cuprum,
Topaz, Taurus, Australian Brown, Spartan Banner 80, Spartan Sleeper, Columbia,
Yellow Globe Danvers strains.
Western Oregon, mineral soils; spring seeded, yellow:
Early sales-yellow: Progress, Rocket, Granada, Simcoe, Aries, Taurus,
Pronto, Early Pak, Yula.
Storage-yellow: Rocket, Granada, Simcoe, Aries, Taurus, Spartan Ban-
ner, Sentinel, Capable, Autumn Splendour, Improved Autumn Spice, Canada Maple,
Super Sleeper, Spartan Sleeper, Sentinal, Australian Brown, Sweet Sandwich,
Golden Cascade. For trial: Candy, Pinnacle, First Edition (long storage).
Red: Tango, Carmen, Benny's Red. Torpedo (long, spindle-shape, sweet).
For trial: Fuego.
White (white types are only marginally adapted to western Oregon):
Blanco Duro, White Delight.
Medford area:
Yellow: Grenada, Vega, Sweet Amber, Bravado, Brahma, Valdez, Magnum.
White: Avalanche, Blanco Duro, Glacier.
Red: Carmen, Tango, Bennies Red. Torpedo (long, spindle-shaped,
sweet).
Fall seeded over-wintering onions - Yellow: Top Keeper, Hi Keeper,
Buffalo, Keep Well, Hi Ball, Bison, Senshyu Yellow, Imai Yellow, Walla Walla
(a number of Walla Walla onion strains exist: Early and late French, Arbini,
Locati and others; none are hybrids). Red: Red Cross (a large, "Bermuda" or
flat onion), Kurenai. These onions are planted in mid August to mid September
and harvested in late June-July
Dehydration types: See seperate file.
Pearl or cocktail onions; boiler onions and onion sets: See seperate
file.
SEED COMPANIES
Abbott & Cobb Inc. POB F307, Feasterville, PA 19047
Asgrow Seed Company, POB 5038, Salinas CA 93915
American Takii Inc., 301 Natividad Rd. Salinas, CA 93906
Bejo Seeds, 1323 E. Fir St. Mt. Vernon WA 98273
Champion Seed Co. 529 Mercury Lane, Brea, CA 92621-4894 714/529-0702
Crookham Co. Caldwell, ID 83606
Dakota Seed International Inc. POB 5467, Saginaw, MI 48603
Ferry-Morse Seed Co. POB 4938, 555 Codoni Ave. Modesto, CA 95352
Harris Moran Seed Co. 3670 Buffalo Rd. Rochester, NY 14624
Petoseed Co. Inc. POB 4206, Saticoy, CA 93303
Rio Colorado Seeds, Inc. 4701 Gila Ridge Road, Yuma AZ 85365
Scottseed. 4876 N. Road H. Vale OR 97918 503/473-3246
Shamrock Seed Co., Inc. POB 4443 Salinas, CA 93912
Sluis & Groot of America Inc. 124 Griffin Street, Salinas, CA 93901
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
SOIL TEMPERATURE
The optimum temperature range for germination is 48 to 90 F. March and
April plantings are most common in western and central Oregon.
SOILS
In western Oregon, onions are grown on peat soils or silt loams and
sandy loams. Overwintered crops must have soils with good internal drainage.
SEEDING AND TRANSPLANTING
In western Oregon planting is from approximately the 20th. of March through
the first week of May.
Onion seed numbers approximately 9,500 per ounce. Most onions are
direct seeded. A few acres of overwintering Walla Walla Sweet onions are
transplanted in northern Umatilla County. Some later varieties of sweet
Spanish onion are transplanted in the Willamette Valley.
About 120,000 to 140,000 transplants are needed to plant one acre (when
planted 3-4 inches apart in rows 15 - 24 inches apart). Only garden onions are
grown from sets. When sets are used, about 800 lbs of 15/16 inch or smaller
diameter sets, are needed per acre. The depth of transplant or set placement
has an effect on onion shape (see section on seeding below).
Precision Seeding
This method of placing individual seeds at a predetermined spacing
within a row produces a crop of more uniform size, less culls and higher yield
of the desired size grade. Present recommendations are to use coated seed and
to seed two lines 3 in. apart per row with 6-12 seeds per ft. of row (depend-
ing on variety), and rows 10-12 inches apart. Stanhay, Beck, or Graymore
planters are used with coated seed. New vertical plate vacuum planters such
as the Gaspardo or Stanhay also may be used with uncoated seed.
Spring Seeding:
Onions may be seeded as soon as the land can be made ready, but mid-
April is considered ideal. If seeded too late, bulbs will be small since
bulbing will begin before adequate growth occurs. Seeding should be completed
by May 5 in Western Oregon.
Approximately 2-3 lbs. of seed are required per acre when using a Planet
Junior planter with 2 to 4 inch scatter shoe. Planters should be set to drop
5-10 seeds per foot of row (depending on the variety and size of onion to be
grown), 3/4 to 1 inch deep.
Depth of seeding has an effect on bulb shape since the onion stem plate
(the base of the onion bulb) forms at the point where the seed germinates.
Shallow planting results in flatter bulbs, while deeper seed placement results
in taller, and sometimes top-shaped bulbs.
Spacing between rows is usually 10-12 inches apart in Western Oregon,
where sets of 4 or 5 rows are used between wheel spacings.
Fall Seeding:
Over-wintered onions are seeded in August to mid September. The earlier
seeding dates are preferred with the more bolting resistant varieties. Plant
spacings and configurations are the same as described above, except that final
spacings should be 3-4 plants per foot of row to obtain the jumbo sizes desi-
red in these types of onions. Over-wintered onions are grown for their mild-
ness and succulent texture which will not stand crowding. Over crowding will
cause these onions to become badly misshapen and flat-sided.
It has been observed that temperatures under 20 F. during the winter
months may lead to thickened and elongated necks at harvest that cure poorly.
Some varieties (Walla Walla Sweet) are more susceptible to this problem than
other varieties recommended.
Transplant Production:
Sow 2-3 lb. of seed to obtain enough plants for each acre to be trans-
planted. One acre of seed-bed can produce enough transplants for 12 acres of
onions. Seed is drilled to a depth of l in. or slightly less.
Seed may be drilled with a wide shoe attachment which scatters the seed
over a 4 in. band in rows with 16 in. centers. Light sprinkler irrigation
following seeding will often be necessary to obtain a satisfactory stand.
Loosen plants before pulling, and tie in bundles of 100 to 200. If
being moved any distance, or if transplanting will be delayed, store at 32- 36
F with relative humidity of 90%. Immediately before planting, trim the plants
to leave l/2 in. of the original root and 4 in. of the green top. Set in rows
12-16 in. apart, with 3-4 in. between plants.
FERTILIZER
The following guides for western Oregon onion fertility management have
been quoted from OSU Fertilizer Guide 67 (for western Oregon muck soils) and
are based on muck soil and mineral soil research conducted by faculty of the
Soils and Horticulture Departments of Oregon State University.
Western Oregon Mineral Soils:
Spring seeded onions:
A soil test is the most accurate guide to fertilizer requirements.
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.
Because of the influence of soil type, climatic conditions, and other
cultural practices, crop responses from fertilizer may not always by accurate-
ly predicted. Soil test results, field experience, and knowledge of specific
crop requirements help determine the nutrients needed and the rate of applica-
tion. Fertilizer application for onions should insure adequate levels of all
nutrients. Optimum fertilization is essential for top quality and yields.
Fertilizer suggestions are based on a 12"-14" row spacing. Recommended
soil sampling procedures should be followed in order to estimate fertilizer
needs.
NITROGEN (N):
N rate of 20-40 lbs/A should be broadcast and worked into the seedbed
before planting, using fertilizers such as ammonium sulfate, 16-20-0 or a
mixed fertilizer containing sulfate sulfur. Note: When mild-flavored onions
are desired, reduce sulfur applications to the minimum recommended for proper
plant growth since sulfur applications have been shown to increase onion
pungency (see sections on "sulfur" below).
An additional 100-120 lbs/a should be applied during the growing season
when onions are 6-8" tall.
Fall seeded overwintering onions:
Use only 30-50 lbs of N/A at time of planting. Apply all additional N
in the spring in March, April and May. Be careful to minimize growth in the
fall (by limiting N and water applica- tions) so that plants go into the
winter about 1/4 inch in diameter otherwise excessive bolting will occur in
the spring.
Sidedressed nitrogen applications or nitrogen applied in irrigation
water can be an effective means of providing supplemental nitrogen to the crop
during the season. DO NOT use aqua or anhydrous ammonia in sprinkler irriga-
tion.
Nitrogen liquid fertilizer formulations having herbicidal effects:
AN-20, Ammonium Thiosulfate and mixtures of these two materials can be
used in a number of crops. Monocarbamide Dihydrogensulfate (Monourea sulfuric
acid) is used in Alliums such as onion, shallots, leeks and garlic. The
amount of nitrogen per gallon of material, the rate at which it is applied,
and the phyto-toxicity of the material determines what crops these can be used
on.
Monocarbamide Dihydrogensulfate (Monourea sulfuric acid) is also sold as
an herbicide under different trade names (see below). ALWAYS FOLLOW THE LABEL
WHEN USING THIS MATERIAL AS AN HERBICIDE.
All of these materials, when applied at the proper time and manner have
the added benefit of ancillary control of many small (less than 3 inches)
broadleaf weeds such as groundsell, pineapple weed, shepherdspurse, mallow,
pigweed, hairy nightshade chickweed and many others. Poor, or no control is
obtained on lambs quarters, purslane, henbit, black nightshade, knotweed, sow
thistle, malva goosefoot and grasses.
When using these nitrogen sources in foliar applications, follow cau-
tions listed. Severe crop injury may occur if cautions are not observed.
General cautions that apply to nitrogen liquid fertilizer formulations are:
* Apply to onions only after the first true leaf is as tall as the flag
leaf and before onions are 8 inches tall.
* Do not apply within 4 days of a period of cool, cloudy or rainy
weather, or if free water is present on the leaves.
* Discontinue application if spray droplets do not roll off or "bead-
up" on the leaves. This indicates a deficiency of adequate waxy cuticle, and
may be a temporary condition due to rapid growth, cloudy or rainy weather, or
more seriously, the lack of adaptability of the variety.
* Do not apply within 4 days after a foliar pesticide has been applied,
or with any wetting agent.
* Use large nozzles to minimize misting and possible injury to the crop
growing point.
AN-20 fertilizer formulation:
This is a manufactured 20-0-0 formulation (containing 20% N) that may be
applied at 50 to 70 gallons of product per acre as a foliar spray. This
formulation weighs 10.55 lbs per gallon and contains 2.11 lbs N/gallon of
product and would provide approximately 100 to 140 lbs N/acre (but some N is
lost through volatilization). Do not irrigate for 48 hours after application,
but irrigate then to move the fertilizer into the root zone.
When this treatment is used, subsequent nitrogen side dressings should
be reduced by a portion of the amount of N applied in the treatment.
Note: Mixtures of An-20 and Ammonium thiosulfate (usually 1:1) can be
made which will reduce the amount of nitrogen applied, provide some sulfur (if
AN-20 only would have been applied, and reducing the sulfur if only Ammonium
thiosulfate were to be used), and be as effective as either material alone.
Application rates are still held at 50 to 70 gallons of the mixture per acre.
Note: This formulation is different from a solution that could be
prepared by dissolving ammonium nitrate in water. Such a solution would not
have the same concentration or herbicidal effect.
Also, To prevent crop injury, follow the cautions listed above.
*****
Ammonium thiosulfate:
This is a manufactured 12-0-0-26 formulation (containing 12% N and 26%
sulfur) and weighs 9.33 lbs per gallon. It may be applied at 50 to 70 gallons
of product per acre as a foliar spray. This solution contains 1.12 lbs
nitrogen and 2.4 lbs sulfur per gallon of product and would provide approxi-
mately 55 to 75 lbs N/acre (some N may be lost through volatilization). At
the application gallonage mentioned, about 150 to 168 lbs of S are also
applied. Do not irrigate for 48 hours after application, but irrigate then to
move the fertilizer into the root zone.
When this treatment is used, subsequent nitrogen side dressings should
be reduced by a portion of the amount of N applied in the treatment.
Note: Mixtures of An-20 and Ammonium thiosulfate (usually 1:1) can be
made which will reduce the amount of nitrogen applied, provide some sulfur (if
AN-20 only would have been applied, and reducing the sulfur if only Ammonium
thiosulfate were to be used), and be as effective as either material alone.
Application rates are still held at 50 to 70 gallons of the mixture per acre.
Also, To prevent crop injury, follow the cautions listed above.
*****
Monocarbamide Dihydrogensulfate (Monourea sulfuric acid) 15-0-0-16 (n-pHuric
or ENQUIK):
This product is recommended for use on onions (bulb and green), shal-
lots, leeks and garlic only.
This product is also registered as an herbicide to be applied at 10 to
30 gallons of product per acre as a foliar spray. FOLLOW THE LABEL INST-
RUCTIONS WHEN USING IT AS A NITROGEN SOURCE OR AS AN HERBICIDE. It weighs
12.65 lb/gallon and contains 1.9 lbs of nitrogen and 2.0 lbs sulfur per gallon
of product. It is most generally used at about 15 to 20 gallons per acre pro-
viding approximately 28 to 38 lbs of N per acre (but some N is lost through
volatilization). Apply in sufficient water to get good foliar coverage
(approximately 1:1 dilution). Do not irrigate for 48 hours after application,
but irrigate then to move the fertilizer into the root zone.
When this treatment is used, subsequent nitrogen side dressings should
be reduced by a portion of the amount of N applied in the treatment.
CAUTION: This solution is corrosive, and can injure skin and damage
spray equipment. Use proper safety precautions and suitable spray equipment
(stainless steel).
Also, To prevent crop injury, follow the cautions listed above, and
FOLLOW ALL LABEL INSTRUCTIONS.
*****
PHOSPHORUS (P):
Phosphorus is essential for vigorous early growth of seedlings. All
phosphorus should be applied at planting, regardless of whether spring-
seeding or fall seeding. P should be banded at planting 2" to the side and
below the seed.
If the OSU soil test Apply this amount of
for P reads (ppm): phosphate (P2 O5) (lbs/A):
0-40 170-200
40-100 140-170
over 100 100-140
POTASSIUM (K):
All K should be applied and worked into the seedbed before planting.
Onions require medium levels of available soil potassium. The K soil test is
based on K present in the surface soil (0-12").
If the OSU soil test Apply this amount of
for K reads (ppm): potash (k2 o) (lbs/A)
0-100 150-200
100-200 100-150
200-350 50-100
Over 350 0-50
MAGNESIUM (Mg):
When the soil test value is below 1.0 meq Mg/100g, broadcast 20 to 25 lb
Mg/A and work into the seedbed before planting. If deficiency symptoms
appear, spray with 10 lb Epsom salts in 100 gal water/A.
Mg can also be supplied in dolomite, which is a liming material and
reduces soil acidity to about the same degree as ground limestone. Dolomite
should be mixed into the seed bed in the fall.
BORON (B):
No consistent responses of onions to the application of B have been
observed in western Oregon. Where the soil test for B is below 0.25 ppm
growers may wish to make a trial application of 2 lb B/A. Too much B ferti-
lizer can be highly toxic and suggested rates of B application should not be
exceeded. B should be evenly distributed over the field and not banded.
ZINC (Zn):
The application of Zn has increased the yield of onions where soils have
been deficient. When the soil test for Zn is below 2 ppm broadcast 10 lb Zn/A
before planting or include 3-4 lb Zn/A in the fertilizer band. A broadcast
application of 10 lb Zn/A should supply Zn needs for 2 or 3 years.
OTHER NUTRIENTS:
Responses of onions to nutrients other than those discussed in this
guide have not been observed in western Oregon.
LIME:
Onions are classified as being "very sensitive to soil acidity" when
grown on mineral soils. Lime applications should be considered when mineral
soil pH is 6.0 or below. Lime should be mixed into the soil in the fall for
best results. Keep mineral soil pH between 6.0 and 6.8.
For acid soils low in magnesium (Mg) (less than 1.0 meq Mg/100 g of
soil) 1 Ton/A of dolomite lime can be used as a Mg source. Dolomite and
ground limestone have about the same ability to neutralize soil acidity.
Western Oregon Muck Soils:
The following recommendations for muck soil onion fertility have been
quoted from OSU Fertilizer Guide 67 based on research conducted by faculty of
the Soils and Horticulture Departments of Oregon State University .
A soil test is the most accurate guide to fertilizer requirements.
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.
Because of the influence of soil type, climatic conditions, and other
cultural practices, crop responses from fertilizer may not always by accurate-
ly predicted. Soil test results, field experience, and knowledge of specific
crop requirements help determine the nutrients needed and the rate of applica-
tion. The fertilizer application for onions should insure adequate levels of
all nutrients. Optimum fertilization is essential for top quality and yields.
Fertilizer suggestions are based on a 12"-14" row spacing. Recommended
soil sampling procedures should be followed in order to estimate fertilizer
needs.
See also the comments in the section "western Oregon mineral soils -
nitrogen" regarding "liquid nitrogen fertilizer solutions having herbicidal
effects" as you consider nitrogen applications on western Oregon muck soils.
NITROGEN (N):
An N rate of 20-40 lbs/A each should be broadcast and worked into the
seedbed before planting, using fertilizers such as ammonium sulfate, 16-20-0
or a mixed fertilizer containing sulfate sulfur. Caution, when mild- flavored
2onions are desired, reduce sulfur applications to the minimum recommended for
proper plant growth since sulfur applications have been shown to increase
onion pungency (see section on "sulfur" below).
An additional 20-60 lbs/acre of nitrogen should be applied during the
growing season when onions are 6-8" tall.
Refer also to the section above "western Oregon mineral soils - nitro-
gen" regarding "liquid nitrogen fertilizer solutions having herbicidal
effects" as you consider nitrogen fertilization.
PHOSPHORUS (P):
P is essential for vigorous early growth of seedlings. P should be
banded at planting 2" to the side and below the seed.
If the OSU soil test Apply this amount of
for P reads (ppm): phosphate (P2 O5) (lbs/A):
0-40 120-150
40-100 80-120
over 100 60-80
POTASSIUM (K):
K should be applied and worked into the seedbed before planting. Onions
require medium levels of available soil potassium. The K soil test is based
on K present in the surface soil (0-12").
If the OSU soil test Apply this amount of
for K reads (ppm): potash (k2 O) (lbs/A):
0-100 150-200
100-200 100-150
200-350 50-100
Over 350 0-50
MAGNESIUM (Mg):
When the soil test value is below 1.0 meq Mg/100g, broadcast 20 to 25 lb
Mg/A and work into the seedbed before planting. If deficiency symptoms
appear, spray with 10 lb Epsom salts in 100 gal water/A.
Mg can also be supplied in dolomite, which is a liming material and
reduces soil acidity to about the same degree as ground limestone. Dolomite
should be mixed into the seed bed in the fall.
BORON (B):
No consistent responses of onions to the application of B have been
observed in western Oregon. Where the soil test for B is below 0.25 ppm
growers may wish to make a trial application of 2 lb B/A. Too much B fertil-
izer can be highly toxic and suggested rates of B application should not be
exceeded. B should be evenly distributed over the field and not banded.
ZINC (Zn):
The application of Zn has increased the yield of onions where soils have
been deficient. When the soil test for Zn is below 2 ppm broadcast 10 lb Zn/A
before planting or include 3-4 lb Zn/A in the fertilizer band. A broadcast
application of 10 lb Zn/A should supply Zn needs for 2 or 3 years.
COPPER (Cu):
Muck soils tend to be deficient in Cu and "fix" Cu. If Cu has not been
applied for 3 years , apply 15-25 lb Cu/A to the soil before planting, OR two
foliar applications of 1-2 lb Cu in 100 gal water /A may be applied to onion
leaves. Soil Cu applications need not be repeated every year. The best
indicator for copper is leaf analysis. Consider copper applications when leaf
copper levels are below 4 ppm.
OTHER NUTRIENTS:
Responses of onions to nutrients other than those discussed in this
guide have not been observed in western Oregon.
LIME:
Experimental work on the muck soils of western Oregon has shown that
onions will produce good yields over a fairly wide range of muck soil acidity.
Lime applications should be considered when the soil pH is 5.5 or below. Keep
muck soil pH between 5.6 and 6.0.
The liming rate is based on 100-score lime. A lime application is ef-
fective over several years.
If the OSU soil test Apply this amount
for pH reads: of lime (Tons/A):
below 5.0 4-5
5.0-5.5 2-4
over 5.5 0
Lime should be mixed into the soil in the fall.
For acid soils low in magnesium (Mg) (less than 1.0 meq Mg/100 g of
soil) 1 Ton/A of dolomite lime can be used as a Mg source. Dolomite and
ground limestone have about the same ability to neutralize soil acidity.
Do not apply lime when the muck soil pH is above 6.0. Decreased yields
have resulted in Willamette Valley experiments when liming raised the soil pH
to 6.5.
IRRIGATION
Onions are shallow-rooted, and unless moisture supply is constant, they
bulb early and the resulting sizes may be small. Light, frequent irrigations
should be used when onions are small to minimize leaching of nitrogen from the
root zone. Increase water applications as plants and roots increase in size.
Maintaining moisture near the surface, at the onion stemplate is important in
root generation. Onion roots generate at the stemplate only when moisture is
present. Proper moisture management is important in alleviating pink root
problems, general root health, and therefore bulb growth vigor. Also, main-
taining an even soil moisture is important in reducing incidence of double-c-
enter bulbs.
Irrigation should thoroughly wet the soil to the 24 in. depth. In west-
ern Oregon, 15-20 inches of water may be required. Watering should be termi-
nated after the bulbs have reached full size, and tops have begun to fall.
In overwintering onion production, use fall season water sparingly.
Apply only enough water to establish a good stand, and enough growth so that
onions will over-winter successfully. Onion plants should be about 1/4 inch
in diameter as they go into the winter and go dormant. In spring and early
summer, irrigate as necessary to maintain vigorous growth. Irrigation is
generally terminated in June, prior to harvest.
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.
HARVESTING, HANDLING, CURING, AND STORAGE
In western Oregon, harvest may range from the 20th. of August to the
20th. of October with the prime harvest season being from the first to the end
of September. The average yield of storage onions in Western Oregon is
approximately 20 tons/acre with good yields of about 25 tons/acre.
Studies on the effect of harvest date on yield indicate that yield of
bulb onions increases dramatically in the 4 weeks before 100% tops-down. In
one study, yields increased approximately 10,500 lbs./acre from the start of
top-fall (at 12% tops-down) to 100% tops-down, while mean bulb weight in-
creased 2.25 oz. Furthermore, after the start of 100% tops down, yield
increased by 2900 lbs./acre for the next 5 days (Davis, G.N. and H. Jones).
As onions mature, tops begin to fall and dry. Sprout inhibitors are
applied when onions are intended for long term storage. They are applied when
tops are about 50% down, and there are 5 to 8 green leaves per bulb to absorb
and translocate the sprout inhibitor. Do not apply sprout inhibitors when
temperatures exceed 80-85 F to avoid crystallization on leaf surfaces. Use of
a spray adjuvant is suggested . Avoid early sprays before maturity to reduce
spongy onions. Maleic hydrazide (Royal MH-30) at 2 lbs ai/A is most commonly
used. Apply in sufficient water to insure adequate coverage. CONSULT LABEL
FOR LATEST INFORMATION ON APPLICATION RATES, TIMING AND PRECAUTIONS.
Research indicates that, from the standpoint of maximum storage life
(before bulb sprouting) optimum harvest would be when onion foliage is still
partially (30-40%) erect, and long before maximum yield is attained (when tops
are completely down and dry). Since yields may increase 30-40% between the
stage when tops begin to go down, and the leaves are fully down and dry, it is
tempting to leave onions to cure in the field as long as possible. The
optimum time for harvest therefore, must be a balance between highest yields
and reduced bulb storage quality. Furthermore excessively field-drying onions
increases the risk due to bald onions in storage.
DIGGING AND WINDROWING
To facilitate curing onions for harvest and storage, onion rows are
undercut, lifted and windrowed for field curing. Rod-weeder diggers and
knife undercutters are most common. After an appropriate interval, the
undercut onions are lifted and windrowed. This may be done with tops on or
tops may be removed in the windrowing operation. Onions are also commonly
windrowed with tops on to protect them from sunscald. Windrows may also be
mechanically "fluffed" to facilitate curing.
TOPPING
Onions may be topped or harvested and stored with tops on. Topping may
be done by hand or by machines such as the Vegi-Vac, Top-Air. These machines
perform the lifting, topping and windrowing operations at the same time. When
onions are allowed to cure without windrowing, machines can also harvest, top
and load all in one operation.
With good air movement and proper placement of onions in storage, onions
have been found to store best with their tops on, however, keeping the tops on
may complicate removal of onions from bulk storages and necessitates extra
handling at packing time.
If onions are to be bulk-stored it is best to store them without their
tops. This facilitates handling, loading and unloading the storage. Onions
that are to be stored in bins are usually stored with tops on.
If onions are to be topped and stored, tops must be totally dry, or only
the dry portion cut and removed. Cutting through any portion of the top while
it is still green or moist may result in excessive Botrytis neck rot in
storage. When all or a portion of the onion top is left on, the remaining
tops are removed during grading and packing using roller toppers at the
storage or packing facility.
In the field, mechanically undercut and windrow "storage types" and
pearl onions when 65-100% of the tops are down and cure by windrowing in the
field. Machine "fluffing" of the windrow a few days after digging will
shorten the drying period. This should also be done after each rainfall.
After field drying has occurred, the onions may be topped and placed in
storage buildings. Specialized harvesters are available for the various types
of onions.
Early market and "overwinter" onions for immediate sale or short-term
storage are mechanically undercut and may be green-topped by hand or machine
and partly cured in sacks or boxes in the field prior to packing. Since these
onions are not to be stored, complete curing of necks and scales is not as
important.
When these onions are intended for storage, complete curing is manda-
tory. Care must be exercised in handling these onions to guard against
sun-scald and damage since these onions are much more succulent and have very
few protective scales. When mechanically undercut and windrowed for curing,
be sure onion tops provide adequate protection from sun-scald during periods
of high sunlight and temperature (above 90 F).
Cull onion disposal: Oregon Department of Agriculture regulations
specify rules for cull onion disposal in order to minimize the spread of
diseases. Consult these, for rules appropriate to your production area. In
western Oregon, many of the cull onions are disposed of as sheep feed. Due to
certain chemical constituents of onion, their use in animal feed is restricted
by animal species and feed concentration.
STORAGE (quoted form USDA Ag. Handbook #866):
Storage may be either in bags, crates, in pallet boxes that hold about a
half ton of loose onions, or in bulk bins. Bags of onions are frequently
stored on pallets and should be stacked to allow proper air circulation.
Modern air-cooled storages have forced ventilation systems in which air, heat-
ed if necessary, is introduce through floor racks beneath the bins of onions.
Onions in bins are stored about 10 to 15 feet deep, but soft onions at the
bottom may be distorted in shape.
Onions are held in either common or cold storage. The storage quality
of onions is influenced by cultivar and by the conditions under which they are
grown and stored.
Onions should be adequately cured in the field, in open sheds, or by
artificial means before or in storage. Adequate curing in the field or in
open sheds may require 2 to 4 weeks, depending on the weather. The best skin
color develops at 75 to 90 F. and 60-75% relative humidity. The most common
method of curing in northern areas is by forced ventilation in the storage by
blowing heated air at 75 to 85 F through the onions at 2 cf./m. air flow per
cubic foot of onions. Electric or gas-fired infrared radiation has been shown
to be an effective heating system for rapid curing.
Onions are considered cured when the neck is tight and the outer scales
are dry and will rustle. This condition is reached when onions have lost 3 to
5% of their weight. If not adequately cured, onions are likely to decay in
storage. The most common form of decay is gray mold rot, which occurs at the
top of the bulb - whence its name "neck rot".
In the northern onion-growing states, onions of globe types are general-
ly held in common storage. Average winter temperatures in the principal
northern onion-producing states are sufficiently low to permit common storage
during the winter months. However, they should not be held after early
January unless they have been treated with maleic hydrazide in the field to
reduce sprout growth.
Refrigerated storage is often used for onions to be marketed late in the
spring. Onions to be held in cold storage should be placed there immediately
after curing. A temperature of 32 F will keep onions dormant and reasonably
free from decay, provided the onions are sound and well cured when stored.
Air circulation should be sufficient to prevent heating and to remove moisture
from within bins or sacks.
Sprout growth indicates too high a storage temperature, poorly cured
bulbs, or immature bulbs. Root growth indicates too high a relative humidity.
A comparatively low relative humidity (65 to 70 %)is recommended for success-
ful storage of onions. However, humidities as high as 85 % and forced-air
circulation have given satisfactory results. Higher humidities, at which most
other vegetables keep best in storage, dispose onions to root growth, rot, and
surface mold. Excessive drying however may result in cracking of the outer
bulb scales and bald onions.
Globe onions can be held for 6 to 8 months at 32 F. The mild types such
as those produced in the Walla Walla area of Washington can be held in cold
storage; but, because of their poorer keeping qualities, they usually are
stored for much shorter periods (1-2 months at 32 F.) than the standard globe
cultivars.
Onions will sprout and decay rapidly when stored at temperatures between
40 and 50 F. However, they will not sprout or be as susceptible to decay if
they are in the resting stage, which lasts 30 to 60 days. The resting of most
cultivars is completed during storage at 32 F.
Onions are damaged by freezing, the damage appearing as water soaked
scales when the thawed onions are cut. Onions only slightly frozen may reco-
ver with little perceptible injury if allowed to thaw slowly and without hand-
ling.
Translucent scale of onions (a clearing of the scales which somewhat re-
sembles freezing injury) has been found particularly in large bulbs stored
several months. Prompt cold storage after curing reduces its prevalence.
Onions should not be stored with other products that tend to absorb
odors. They may be stored with garlic.
When onions are removed from storage in warm weather, they are apt to
sweat because of moisture condensation. This may favor decay. Warming onions
gradually, for example, to 50 F over 24 to 36 hours with good air movement
should avoid this difficulty.
Onions can also be stored at high temperatures of 85 to 95 F for short
periods before marketing or before processing. Dehydrated flakes produced
from onions that had been stored at 85 F for 4 months discolored less in stor-
age than flakes made from onions stored at cold temperatures.
Controlled atmosphere storage tests with onions have been only moder-
ately successful. An atmosphere of 5% carbon dioxide with 3% oxygen reduced
losses from sprouting and root growth.
In Oregon curing is generally accomplished by forcing air of a low rela-
tive humidity through the bottom of the onion pile to the top. One to two
cubic feet of air per minute for each cubic foot of onions is recommended,
with the higher air-flow rate used initially to remove surface moisture and
seal necks. If the weather is cool and wet, forced air at 75 to 85 F and 60-
70% relative humidity is recommended. If the onions are also wet, forced air
at 85 F and a relative humidity of 25-35% relative humidity should be used as
soon as storage loading is completed. This should be continued until the
outer skins and neck are dry. The crop should then be allowed to cool gradu-
ally slowly reducing its temperature by drawing outside air, anytime the stor-
age air has a humidity above 75% and the outside air is cooler than the
onions, until the temperature of the onions reaches the desired holding tempe-
rature, or (32 F and above).
After curing, the relative humidity in the storage should be maintained
between 60 and 70%. If the storage is too dry, the outer bulb scales will
crack excessively, resulting in bald onions during packing. The less fluctua-
tion the better.
During dry, cold weather (above 32 F) the doors may be opened or the
fans used to circulate cold air throughout the pile. Be sure that the dew
point of the outside air that is used is always 2 or more degrees above the
temperature of the onions in the pile, otherwise water may condense on the
onions. During wet weather or very cold weather (below 32 F) the building
should remain closed and the air within should be recirculated periodically or
outside and inside air may be mixed as needed to keep onions cool and dry.
Consult also other appropriate storage publications such as Oregon State
University PNW 277 Onion Storage Guidelines for Commercial Growers.
PACKAGING
Dry onions are sorted, cleaned sized and graded, just prior to packag-
ing. They are commonly packaged in 50 lb. sacks. Some are now also packaged
in consumer packs of 2, 5 and 25 lbs. mesh sacks.
SHIPPING
Dry bulb onions from the northwest are shipped across the U.S.A. at
ambient temperatures but protected from freezing. When shipped international-
ly, several methods are used.
When non-refrigerated containers are used, one door should be removed to
eliminated the build up of humidity from onion respiration. Shipping compa-
nies can arrange to do this.
When refrigerated containers are used, as is necessary with sweet onions
that have limited storage characteristics, arrangements must be made to bring
the temperature in the container to ambient 24-48 hours before arrival at
destinations where local humidity may result in the onions getting wet from
condensation. Arrange for the shipping company to raise the container
temperature from 32 F. to 50 F. 2 days before arrival, then from 50 F. to 70
F. 1 day before arrival. This gradual increase in temperature will prevent
condensation on onions upon their removal from the container and reduce risk
of spoilage.
PEST CONTROL FOR ONIONS, DRY BULB
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
Onions are a noncompetitive crop with short, vertical leaves that fail to
form a canopy that suppresses weeds. Weeds are managed with selective
herbicides combined with frequent cultivation. Winter cover crops or
crop rotations enhance both soil and weed management.
______________________________________________________________________________
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
(see remarks)
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
prepartion or preemergence crops listed on the label. Consult label for
specific rates, times of application, and perennial species controlled.
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 nonlabeled crops within
12 months following application. (Inhibits production of 3 amino acids
and protein synthesis.)
______________________________________________________________________________
ONIONS--MINERAL SOILS
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
bensulide 3 to 6 lb ai/A
Prefar
(spring planted
bulb onions only)
Idaho, Oregon and Washington special local needs (SLN-ID840011 and
OR840041 and WA880015) only. Apply 3 lb rate in fall in 10-12 inch band
and bed-up by throwing soil from furrows over the sprayed band, or
broadcast 6 lb rate and incorporate before bedding up in the fall. In
spring, drag-off bed tops with spiketooth harrow being careful not to
expose soil beneath the treated layer. Plant in center of beds.
(Inhibits roots of seedlings).
------------------------------------------------------------------------
DCPA 6 to 9 lb ai/A
Dacthal
Apply after planting to moist soil surface before weeds and onions
emerge. In eastern Oregon when rainfall is sparse, shallow incorpora-
tion using a nailboard has improved weed control. Results are improved
with overhead irrigation immediately following application. Consult
label for planting sensitive crops within 8 months. (Inhibits mitosis).
------------------------------------------------------------------------
oxyfluorfen 0.12 to 0.25 lb ai/A
Goal
Causes skin irritation--Wear protective gear. Apply postemergence to
onions with 2 fully developed true leaves while broadleaf weeds have
less than 4 true leaves. Multiple treatments may be required as new
weeds emerge, but do not exceed 0.5 lb ai/A. Use a clean sprayer and do
not mix with oils, surfactants, or other agricultural chemicals. Do not
apply to onions under any stress. Slight leaf curl may occur and young
plants sometimes become prostrate on the soil surface for 1 to 2 days,
but yields have not been reduced. Do not apply within 60 days of
harvest. (Acts as a selective contact that disrupts cell membranes).
Special local needs (SLN-OR-90026 and WA-910012 allows application
through sprinkler irrigation systems. Read and follow label instruc-
tions precisely regarding irrigation interval and all chemigation
specifications to minimize environmental hazards.
------------------------------------------------------------------------
monocarbamide 10 to 30 gal
dihydrogensulfate product/A
Enquik
Apply in sufficient water volume for full coverage when first true leaf
is as tall as flag leaf. Repeat applications may be necessary. Do not
apply in presence of free moisture or within 5 days after a foliar
pesticide application. Repeat as required until crop is 8 inches tall;
then direct sprays between rows. Do not apply to green onions after
they reach 8 inches to avoid scarring. Adjust fertilizer rates for
nitrogen and sulfur. (Acts as contact).
------------------------------------------------------------------------
bromoxynil 0.25 to 0.38 lb ai/A
Buctril
Do not ingest or inhale spray mist and prevent contact with skin.
Wearing protective face shields, respirators, and clothing is advised.
For use in Idaho and east of the Cascades in Oregon and Washington only.
Apply in 50 to 70 gal water for thorough coverage when onions have 2 to
5 true leaves. Apply on sunny days when plants are dry and humidity is
low. Do not apply west of the Cascades or when the protective waxy
cuticle on onion leaves may be thin or damaged. Application can be
preemergence, but irrigation or rainfall within 2 days of application
may result in crop injury. Do not add adjuvants. Injury can sometimes
occur even under ideal conditions. (Precise action unknown; acts as a
selective contact that disrupts cell membranes).
------------------------------------------------------------------------
pendimethalin .5 to 1.48 lb ai/A
Prowl
(dry bulb onions
only)
Apply postemergence when onions have 2-9 true leaves and at least 45
days before harvest. Adjust rates according to soil texture. Rainfall
or overhead irrigation is needed within 10 days for activation. Be
aware of crop rotation restrictions including sugar beets, winter wheat,
and winter barley. (Inhibits mitosis, both in shoots and roots).
------------------------------------------------------------------------
trifluralin 0.38 to 0.63 lb ai/A
Treflan (broadcast rates)
Apply at lay-by as a directed spray to the soil between rows and incor-
porate immediately with sweeps or rolling cultivators. Use proportion-
ately less for treating area between rows only. Do not apply to soils
with more than 3.5% organic matter or reduced herbicide activity will
result. Do not apply preplant or preemergence or within 60 days of
harvest. Remove emerged weeds before application. Consult label for
planting sensitive crops within 12 months. (Inhibits mitosis, both in
shoots and roots).
------------------------------------------------------------------------
paraquat 0.625 to 0.94 lb ai/A
Gramoxone Extra
A restricted-use pesticide. Do not ingest or inhale spray mist.
Wearing protective face shields, respirators, and clothing is advised.
Apply before, during, or after planting, but preemergence to crop to
control emerged weed seedlings only. 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 precipi-
tates. Preharvest interval is 60 days. (Acts as contact; absorbs energy
produced by photosynthesis forming peroxides that disrupt living cells.
------------------------------------------------------------------------
fluazifop Consult Label
Fusilade 2000
Identify grasses and adjust rates depending on suceptibility and stage
of weed growth according to label instructions. Apply to actively
growing grasses as a directed spray with 1% crop oil or 0.25% nonionic
surfactant. Erratic results often occur when grasses are stressed from
lack of vigor, drought, high temperature, low fertility, grass stage of
growth, and unknown environmental factors. More mature grasses and
quackgrass can be controlled but may require two applications. Annual
bluegrass and all fine fescies resist treatment. Do not harvest within
45 days of treatment or apply more than 6 pints product per year.
Grazing is prohibited. (Inhibits fattyacid production, cell membranes,
and new growth.)
------------------------------------------------------------------------
sethoxydim 0.19 to 0.28 lb ai/A
Poast
Identify susceptible grasses and apply at optimum growth stage listed on
the label. Add 2 pints/A nonphytotoxic crop oil concentrate to improve
leaf absorption. Erratic control often occurs when grasses are stunted
or stressed from drought, high temperatures, or low fertility. Resis-
tant grasses include annual bluegrass and all fine fescues, whereas
quackgrass can be suppressed. Do not apply within 30 days of harvest,
nor exceed 4.5 pints/A per season. (Inhibits fatty acid production,
cell membranes, and new growth.)
______________________________________________________________________________
MUCK OR PEAT SOILS
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
oxyfluorfen 0.12 to 0.25 lb ai/A
Goal
Apply postemergence to onions with 2 fully developed true leaves while
broadleaf weeds have less than 4 true leaves. Multiple treatments may
be required as new weeds emerge, but do not exceed 0.5 lb ai/A. Use a
clean sprayer and do not mix with oils, surfactants, or other agricul-
tural chemicals. Do not apply to onions under any stress. Slight leaf
curl may occur and young plants sometimes become prostrate on the soil
surface for 1 to 2 days, but yields have not been reduced. Do not apply
within 60 days of harvest. (Acts as a selective contact that disrupts
cell membranes).
------------------------------------------------------------------------
monocarbamide 10 to 30 gal product/A
dihydrogensulfate
Enquik
Oregon special local needs (SLN-OR850029) label. Apply in sufficient
water volume for full coverage when first true leaf is as tall as flag
leaf. Repeat applications may be necessary. Do not apply in presence
of free moisture, nor within 3 days after a foliar pesticide applica-
tion. Do not apply to green onions after they reach 8 in. to avoid
scarring. Adjust fertilizer rates for nitrogen and sulfur. (Acts as
contact).
------------------------------------------------------------------------
fluazifop Consult label
Fusilade 2000
Identify grasses ad adjust rates depending on susceptibility and stage
of weed growth according to label instructions. Apply to actively
growing grasses as a directed spray with 1% crop oil or 0.25% nonionic
surfactant. Erratic results often occur when grasses are stressed from
lack of vigor, drought, high temperature, or low fertility. More mature
grasses and quackgrass can be controlled but may require 2 applications.
Annual bluegrass and all fine fescues resist treatment. Do not harvest
within 45 days of treatment or apply more than 6 pints product per year.
Grazing is prohibited. (Inhibits fatty acid production, cell membranes,
and new growth).
------------------------------------------------------------------------
sethoxydim 0.19 to 0.28 lb ai/A
Poast
Identify susceptible grasses and apply at optimum growth stage listed on
the label. Add 2 pints/A nonphytotoxic crop oil concentrate to improve
leaf absorption. Erratic control often occurs when grasses are stunted
or stressed from drought, high temperatures, or low fertility. Resistant
grasses include annual bluegrass and all fine fescues, whereas quack-
grass can be suppressed. Do not apply within 30 days of harvest, nor
exceed 4.5 pints/A per season. (Inhibits fatty acid production, cell
membranes, and new growth).
------------------------------------------------------------------------
paraquat 0.625 to 0.94 lb ai/A
Gramoxone Extra
A restricted-use pesticide. Do not ingest or inhale spray mist.
Wearing protective faceshields, respirators, and clothing is advised.
Apply before, during, or after planting, but preemergence to crop to
control emerged weed seedlings only. 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 percipi-
tates. Preharvest interval is 60 days. (Acts as contact; absorbs
energy produced by photosynthesis forming peroxides that disrupt living
cells.)
______________________________________________________________________________
ONIONS-SPROUT INHIBITION
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
maleic hydrazide 2 lb ai/A
Royal MH-30
Apply when bulbs are fully mature with soft necks and 5 to 8 green
leaves, or when approximately 50% of the tops have fallen, but are still
green. Should be applied at temperatures below 80 to 85 F to avoid
crystalization on leaf surfaces. Use of a spray adjuvant is suggested
in arid regions west of the Rocky Mountains. Avoid early sprays before
maturity to reduce spongy onions. Do not treat seed onions.
______________________________________________________________________________
______________________________________________________________________________
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
---------------------------------------------------------------------------
Cutworms and Armyworms Lannate - 0.45 to 0.9 lb
Different species
Bacillus thuringiensis - 1 to 2
Small to large larvae that chew qt. Use a spreader-sticker to
holes in bulbs and leaves. enhance control.
Phosdrin - 0.25 to 0.5 lb
Climbing cutworms only.
Permethrin - 0.1 to 0.3 lb
---------------------------------------------------------------------------
Brown wheat mite
Petrobia latens
Small, light tan to brown active
mite. Damages leaves.
---------------------------------------------------------------------------
Bulb mites soil fumigation
Rhyzoglyphus sp.
Small, white mites capable of causing
damage to developing bulbs and intro-
ducing pathogenic fungi. Damage can
continue in storage.
--------------------------------------------------------------------------
Onion thrips azinphosmethyl -
Thrips tabaci 0.5 to 0.75 lb
Adults are small, pale yellow to malathion - 1 to 2 lb
light brown in color with feath-
ery wings. Young are pale yel- Phosdrin - 0.5 lb
lowish-green and wingless.
They feed on onion foliage and diazinon - 0.5 lb
cause it to become white, kill-
ing the tops and reducing Penncap-M - 0.5 lb Apply
yields. only to dry onions. Do not
use on green onions.
WARNING: Microencapsulated methyl methyl parathion - 0.5 to
parathion (Penncap-M) should never 0.83 lb
be sprayed on blooming weeds in
onion fields or adjacent fields. Permethrin - 0.15 to 0.3 lb
If misused, this formulation is
especially hazardous to honey bees Metasystox-R - 0.75 lb Use
and other pollinating insects be- only on Spanish bulb onions.
cause of its strong tendency to
contaminate pollen. Vydate L - 0.25 to 0.5 lb
Do not harvest tops.
Note: Dasanit applied in the seed
furrow for onion maggot control sup- Lannate - 0.45 lb
presses thrips populations in the
early season. This may allow Pyrellin - 1 to 2 pt
growers to reduce foliar sprays.
Oregon, Idaho, and Washington only,
24 c. Caution: Dasanit may reduce
onion stands in sandy/light soils.
---------------------------------------------------------------------------
Onion maggot diazinon - 2 to 4 lb
Delia antiqua
Dyfonate - 1 lb Use Dyfonate
Adult is a fly, pale to dark gray only where organic matter
in color, less than inch in exceeds 10 percent.
size. Larvae are legless, blunt
white maggots that kill seed- diazinon - 1 lb
lings and damage bulbs of Furrow applications only.
older plants.
malathion - 1.5 to 2 lb
Use for adult control.
Lorsban 4E - 0.034 lb ai/1000
row ft. Apply as in-furrow
treatment on direct-seeded dry
bulb onions only.
Lorsban 15G - 0.034 lb ai/1000
row ft. Apply as in-furrow
treatment on direct-seeded dry
bulb onions only.
---------------------------------------------------------------------------
Pea leafminer diazinon - 0.5 lb
Liriomyza huidobrensis
Larvae of tiny fly. Mine in leaves. When
abundant, cause leaves to wither from tip downward.
---------------------------------------------------------------------------
Wireworms diazinon - 3 to 4 lb
Limonius spp.
Telone II or C-17 preplant
Brown, jointed larvae of click beetles.
Kill young plants, weaken older ones.
---------------------------------------------------------------------------
---------------------------------------------------------------------------
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.
ONION -- BASAL ROT
Cause: Fusarium sp., soilborne fungi. The disease causes losses principally of
green onions and garlic.
Symptoms: Yellowing, wilting, and lack of vigorous growth. Red-brown rot where
roots are attached to the base. The rot and discoloration usually affect all
of the base and upwards into the scales. Sometimes a weft of mycelium
develops over the surface of the base or between the affected scales. Rot may
progress in storage under situations where elevated moisture levels exist.
Infection is often associated with pink root, maggots, or other insect injury.
~Control:
1. Protect plants from insect, fertilizer, or other injury.
2. Rotate crops use well-drained soil.
3. Some soil chemicals have been tried but at present none are being recom-
mended.
In a test in Malheur County, Oregon, the following varieties had less basal
rot when compared to a number of other varieties: `Golden Cascade', `Cima',
`Oro Grande', `Valient', and `Cashe'. Other onion varieties described as
tolerant but not tested in Oregon are `Bronze Reserve', `North Star', `Sassy
Brassy', and `Sentinel'.
---------------------------------------------------------------------------
ONION -- DOWNY MILDEW
Cause: Peronospora destructor, a fungus. This organism survives the winter on
infected plants or on old onion plant material in the field.
Symptoms: Bluish, downy spots appear on the leaves. Plants may be dwarfed,
distorted, and pale green. Spots develop first with a water-soaked appearance,
later taking on a purplish shade. In dry climates, the leaf spots may be white
in appearance. As the spots enlarge, often girdling the leaves, a whitish mold
develops on the surface of the spot, later turning black. Secondary leaves may
develop on infected plants, retarding normal bulb development. Plants are not
often killed, but bulb quality is poor and often spongy.
~Control:
1. Avoid poorly-drained soils.
2. Practice a 3-year crop rotation where possible.
3. Destroy onion plant refuse and cull piles.
4. Eradicate perennial onions or wild onions.
5. There are no resistant varieties of the types grown in Oregon.
6. Spray with one of the following:
a. Mancozeb (dry onions only) at 1.6 to 2.4 lb ai/100 gal/A.
b. Maneb at 1.6 to 2.4 lb ai/A.
c. Ridomil MZ58 at 1.5 to 2 lb product/A.
d. Ridomil/Bravo 8l W at 1.5 to 2 lb product/A.
e. Fosetyl-Al (Aliette) at 1.6 to 2.4 lb ai/A.
f. Fixed copper.
Residues:
Mancozeb - Tolerance 0.5 ppm. Do not apply within 7 days of harvest.
Do not apply to exposed bulbs.
Maneb - Do not apply more than 16.8 lb ai/A/season. Do not apply within
7 days of harvest.
Fosetyl-Al -- Do not apply within 7 days of harvest.
Ridomil/Bravo 81W - Do not apply to dry bulb onions within 7 days of
harvest or to green onions within 21 days of harvest or more
than 4 times on green onions. See product label for rota-
tion restrictions.
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ONION -- NECK ROT
Cause: Botrytis allii, a fungus. This organism survives the winter on dead
plant parts in the soil and on infected bulbs. The most common causes for
severe losses are (1) use of excessive amounts of nitrogen which delay
maturity of the crops, (2) irrigation and/or rainfall late in the season, (3)
inadequate or improper curing, and (4) improper storage.
Symptoms: The organism appears on maturing bulbs just prior to harvest and
during harvest, with infection occurring through the neck tissue or through
wounds in the bulbs. Frequently infection enters the neck as a result of
topping the onions prior to proper drying of soft susceptible top tissues. The
fungus moves rapidly into the succulent onion bulb in the neck region,
producing a water-soaked appearance. Yellow discoloration often appears.
Between the onion scales a gray mold develops, later producing small, black
bodies (sclerotia) which develop as a solid layer around the neck. Ultimately
the bulbs break down to a soft mass, and secondary infections follow.
~Control: The tops should be allowed to mature well, and the onions should then
be lifted or undercut. If normal dry weather prevails, the onions should then
cure on the ground for 6 to 10 days. Bruising and mechanical injury in topping
and storing should be kept to a minimum, and the onions should be stored in
well-ventilated houses at temperatures of 32 F or just slightly higher. Higher
temperatures should be used when humidity cannot be held below 75 percent RH.
There are no fungicides that consistantly control neck rot even though EPA has
granted several labels for this use.
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ONION -- NEMATODE (Stubby Root)
Cause: Paratrichodorus allius. An ectoparasitic nematode that overwinters in
the soil. The largest populations of nematodes and conspicuous plant symptoms
occur during cool, damp springs.
Symptoms: Roots are extremely short with yellow to brownish cast plants are
stunted usually in spots in the field.
~Control:
1. Telone II at 4.5 to 36 gal/A (follow label recommendations). Fumigate in
the fall.
OR
2. An in-furrow spray of 1.5 to 2 gal Vydate L (broadcast basis) in 20 to 50
gal of water or .75 to 1 gal Vydate L (broadcast basis) as an in-furrow drench
in 100 to 150 gal of water are usually adequate to control the problem. In
situations with extremely high nematode presence, two or three postemergence
applications may be made. See label--Oregon only (SLN OR 810033).
Residues: Telone II. Preplant soil treatment. Seal soil for 7 to 14 days then
aerate 1 week for each 10 gal/A applied--longer in case of heavy rains or
temperatures below 60 F--until the odor of the fumigant is gone. Do not treat
extremely heavy soils. Do not apply near living plants. Considered to be a
nonfood use.
Soil fumigants. If fall fumigation is done, beds will be free of fumigant by
spring planting.
Vydate. Limit 14 days before harvest. Such late applications will not be
effective in any case.
Sampling: Stubby-root nematodes are migratory ectoparasites (see Nematodes--
Life Histroy), and are found only in the soil. Before planting crops suscep-
tible to stubby-root nematodes, soil samples should be taken with sufficient
lead time to implement management procedures if necessary. If this is soil
fumigation, it may be several weeks before crops can be planted. Fall
sampling for crops to be planted the following spring is an excellent strate-
gy. For diagnosis, submit both soil and onions containing roots.
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ONION -- PINK ROOT
Cause: Pyrenochaeta terrestris, a fungus. This fungus may live in the soil
saprophytically for several years.
Symptoms: The disease may appear either in young seedlings or later throughout
the growth of the onion. There is a yellowing of roots followed by a
pinkish-colored root development. These take on a bright-pink shade and die.
New roots produced thereafter become diseased and also die. As this process
continues through the growing season, the bulbs lack normal development and
are reduced in size and vigor with stunted tops.
~Control:
1. A crop rotation in which onions are planted only every 5 years will reduce
the severity of infection however, some plants will be invaded by the fungus.
2. Use adequate fertilizer, irrigation, cultivation, etc., to stimulate rapid
bulb growth.
3. Some partially resistant varieties of the sweet spanish type are avail-
able.
4. Preplant soil fumigation with Telone C-17 is effective in control of the
disease on mineral soils at the rate of 5.1 to 41 gal/A. Not effective on peat
soils. Note: Fall fumigation is more effective than spring.
5. The varieties `El Capitan', `Avalanche', `Bullseye', `Bravado', `Merit',
`Durango', `Yula', `Armada', `Valdez', and `Fiesta' were bred for resistance.
`Yellow Globe Danvers' types are resistant.
Caution: Since the fumigation must be done prior to planting, it is important
that the planting row be directly over the fumigated soil when only the
planting row is treated. Variations of a few inches can cause complete loss of
control. Not effective on peat soils.
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ONION -- PURPLE BLOTCH
Cause: Alternaria porri, a fungus. The organism overwinters on dead, diseased
onion trash in the field and on infected bulbs. Infection often follows injury
caused by other fungi, e.g., Botrytis, or by sand or dust during windstorms.
The spores require rain or persistent dew to cause infection. The optimum
temperatures are 77 to 81 F. Almost no infection occurs below 55 F. The
disease is sometimes severe in irrigated onion-growing areas of eastern
Oregon.
Symptoms: On the leaves a small, water-soaked area develops, which soon turns
brown. As the spot enlarges, zones may appear, and it turns purplish. White
margins often encircle the purplish centers. When the weather is moist, the
surface of the spot usually becomes covered with a brownish-black, powdery
fungus growth. Leaves with large spots turn yellow and are blown over by the
wind. Infection of the leaves may be noticed by the presence of leaf spots
very soon after infection has occurred, sometimes within 2 days.
Bulb decay may occur during and after harvest. It shows first as a watery rot
starting around the neck and is particularly noticeable because of the
yellowish to wine-red discoloration in the neck region. As the fungus moves
through the onion tissues, they dry and take on a papery texture toward the
outside. `Sweet Spanish' onions are very susceptible to purple blotch.
~Control: The disease does not occur in Oregon with sufficient frequency to
warrant an annual spray program. Spraying as soon as the disease occurs will
prevent further spread of the disease. The variety `Fiesta' has tolerance.
Other control practices which will reduce losses are:
1. Destroy old onion cull piles.
2. Handle and harvest with care, destroying any diseased onions.
3. Proper curing of bulbs in field--lift and allow to dry several days before
topping.
Spray: Mancozeb (dry bulb onions only) (Dithane M-45, Manzate 200)--1.6 to 2.4
lb ai/100 gal/A.
Bravo 720 at 1.5 to 3 pt/a (2 pt maximum) on dry bulb onions in sufficient
water to cover.
Maneb at 1.6 to 2.4 lb ai/A. Do not apply more than 16.8 lb ai/A/season. Do
not apply within 7 days of harvest.
Ridomil/Bravo 8l W l.5 to 2.0 lb/A.
Rovral WP--1.5 lb/A in 50 to 100 gal of water.
Spray fixed copper. Several formulations and products are available. See
product labels for rates.
Tolerance: Mancozeb (dry bulb onions only)--Tolerance 0.5 ppm. Do not apply
within seven days of harvest. Do not apply to exposed bulbs.
Maneb--Tolerance 7 ppm. No time limitation.
Bravo 720--Tolerance 5 ppm on green onions, 0.5 ppm on dry bulb onions. Do not
apply within 14 days of harvest (green onions) or 7 days of harvest (dry
onions). Do not apply more than three times per season on green onions. Do not
apply to sweet spanish onions except in Idaho and Oregon.
Ridomil/Bravo - See cautions under downey mildew.
Rovral WP--Tolerance 0.5 ppm. Do not apply within 4 days of harvest.
Copper: Exempt.
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ONIONS -- RUST (Seed Onions Only)
Cause: Puccinia asparagi, a fungus. The fungus actually survives on asparagus
which commonly grows wild along ditch banks of irrigated areas in southern
Idaho and eastern Oregon.
Symptoms: The uredial stage attacks the onion leaves and seed stalks. Light
yellow to orange or reddish, powdery pustules develop. With pustules enlarge-
ment, the leaves or seed stalks become girdled. The affected tissues at and
above the girdling turn yellow and die prematurely, thus reducing seed yield.
~Control: Destroy wild asparagus or spray the asparagus and adjoining onions
with mancozeb.
Residues: See under Onion--Purple Blotch.
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ONION -- SEED TREATMENT
Aids in control of smut, seed decay, and damping-off.
Thiram-- or 2 t/lb or 1 lb product for 10 lb seed for smut.
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ONION -- SMUT
Cause: Urocystis cepulae, a fungus. This fungus survives saprophytically in
the infested soil for several years. It attacks only members of the onion
family including onion, leek, and Welsh onion.
Symptoms: The disease appears first in the stems of the young plant as it
emerges. Infected areas have a raised blisterlike appearance near the ground
level. These rupture to expose black powder masses of spores. Numerous
seedlings are killed during the emergence period, and those which live produce
distorted bulbs having darkish streaks and numerous smutty lesions.
~Control:
1. Pelleted onion seed using Thiram with a methocel sticker has been used in
some areas. Such pelleted seed is applied at the rate of 5 lb/A.
2. Small onion sets and young onion plants may be set out in infested soil
without apparent danger of infection.
3. Control smut by an in-furrow drench at seeding of mancozeb or Maneb at 2.4
lb actual/A (29,000 linear feet of furrow).
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ONION -- SOFT ROT OR STINKING ROT
Cause: Unknown species of Pseudomonas and Erwinia.
Symptoms: First symptoms appear in late June. Either the inner or outer whorl
of leaves, but usually not both, become flaccid and rapidly change from green
to white to brown and collapse to the ground. Soon the disease progresses to
the apparently unaffected parts, with water-soaking and collapse following.
After collapse of the foliage a watery, foul-smelling liquid exudes from the
bulbs.
Further spread of the disease is reduced by warm, dry summer weather. Slightly
affected plants may recover, but usually are distorted and chlorotic. Bulbs
infected late in the season may appear, but decay during storage. The disease
does not spread from bulb to bulb in storage.
This disease has been widely distributed in western Oregon onion-growing
areas, and occurs in Oregon and Southwestern Idaho onion-growing areas. There
is a lower incidence of this disease in furrow or rill-irrigated fields.
~Control:
1. Some control can be obtained by using water from deep wells, rather than
from ditches.
2. Reduce mechanical injuries during cultivation and weeding.
3. Thoroughly cure onions before storing.
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ONION -- WHITE ROT
Cause: Sclerotium cepivorum, a fungus. The fungus can remain viable in the
soil for many years without the presence of the host--probably as long as 8 to
10 years. Other hosts include garlic, leek, shallot, and other allium sp.
Symptoms: The leaves of a diseased plant decay at the base, turn yellow, wilt,
and topple over. The older leaves collapse first. Roots are rotted and the
plant can be easily pulled up. Fluffy mycelium may be present on the remaining
roots and bulb. Affected bulbs may become watery and the outer scales cracked
as they dry and shrink. Small (1/50 inch) sclerotia are formed in affected
parts of the bulb and on the surface, often around the neck. The sclerotia are
smaller and rounder than those of Botrytis (the cause of the neck rot dis-
ease).
~Control: Idaho law forbids the import of sets, bulbs, or other material
infected with white rot. Avoid the movement of contaminated soil or machinery
into clean fields.
Treatment of heavily infected areas of organic soils with 400 lb of methyl
bromide/A tarped has been useful in reducing inoculum in infested fields.
Incorporate 32-40 lb. of Botran 75 WP/A prior to seeding (see label for
specific instructions). This treatment has been erratic on direct-seeded
onions but is more effective when used on sets.
OR
Spray 2 lb of Ronilan 50 WP in a 4- to 6- inch band in 400 gal. of water/A or
in a 2- to 4- inch band in 100 gal of water/A over the seed row. Apply at
least 2 more applications of 2 lb. of Ronilan 50 WP in 100 gal of water/A at
4-6 week intervals.
Residues:
Botran--Soil application before seeding or spray to soil around sets or buds.
Tolerance 5 ppm. Do not plant spinach as a follow-up crop in treated soil.
Ronilan--Do not apply more than 10 lbs. Ronilan/A in one crop season. Do not
apply within 18 days of harvest. Do not apply through any type of irrigation
system.
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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 and
questions to your County Extension Agent or Dr. N.
S. Mansour, Department of Horticulture, Oregon
State University, Corvallis, OR 9733l.
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