From: Brian Lo <dragon@csulb.edu>
Newsgroups: rec.gardens
Subject: FAQ: Lettuce
Date: Wed, 1 Mar 1995 09:09:25 -0800
LETTUCE
Lactuca sativa
VARIETIES
Crisphead types (approximately 60-75 days when direct seeded):
Transplant - Summertime, Ithaca, Fame, Salinas; PennLake (earliest
plantings only). New, for trial when downy mildew is expected: Target, Alpha
(resistant to downy mildew pathotypes I and III), and Bullseye, Top Gun,
Patriot, Warrior (all tolerant to downy mildew pathotypes I, II and III).
Direct Seeding - For harvest periods (before July 15 and after September
1) and when downy mildew can be a problem: Fame, Salinas, Calmar, Calmaria.
New, for trial when downy mildew is expected: Target, Alpha (resistant to
downy mildew pathotypes I and III), and Bullseye, Top Gun, Patriot, Warrior
(all tolerant to downy mildew pathotypes I, II and III).
for trial: Pablo (a red-tinged crisphead).
For harvest between July 15 and Sep. 1: Summertime, Ithaca (heat
tolerant, both need special attention to irrigation and fertility (130-150
lbs. N/A) to produce necessary size.
For Big Vein infected fields where Salinas would be used, use: Pacific.
All these lines may be sensitive to heat stress, and unsuited for production
from July 15 to Sept 1. Red crisphead: Etna.
Batavian or French crisp types (approximately 50-60 days), green ("inter-
mediate" between butterhead and crisphead): Canasta, Nevada (resistant to
downy mildew strains 1,2,3,4).
French crisp (Batavian) types, red: Sierra, Musca.
Bibb types, green (approximately 60 days): Buttercrunch, Summer Bibb, Salad
Bibb, Salina; Little Gem (resistant to downy mildew strains 1,2,3,4).
Miniature bibb types: Vasco, Tom Thumb.
Butterhead types (approximately 60 days): Balisto (dark green, slow bolting,
BWY virus resistant); Vista and Divina (both resistant to downy mildew strains
1,2,3,4); Red Boston, Gento, Butter King, Dark Green Boston, White Boston;
Tania and Prima (downy mildew resistant), Citation, Augusta, Nancy, Little
Gem.
Butterhead types, red: Sangria (resistant to downy mildew strains
1,2,3,4); Red Boston.
Leaf types, green (approximately 50-60 days): Slobolt (non-bolting, BWY virus
resistant), Waldmann's Green (dark green, slow bolting), Loriol (light green,
slow bolting); Salad Bowl, Green Ice, Royal Green, Grand Rapids.
Leaf types, red: Garnet, Prize Head, RedPrize and New Red Fire (all are
slow-bolting and BWY virus resistant); Deep Red, Red Sails.
Oak Leaf types (approximately 50-60 days), green: Krizet (bolting and BWY
virus resistant).
Oak Leaf types, red: Raisa (dark red), Brunia (both Raisa and Brunia
are resistant to bolting and BWY virus); Red Salad Bowl.
Cos (Romaine) types (approximately 65 days), green: Paris Island Cos (bolting
resistant, vigorous growth), Green Towers, Paris White, Valmaine (downy mildew
resistant). For Trial: Cosmo, Alpi.
Cos (Romaine) types, red: Majestic Red (slow bolting and resis-
tant to BWY virus), Feria.
Stem Lettuce (approximately 85 days): Celtuce (for specialty Oreintal mar-
kets).
SEED COMPANIES
Asgrow Seed Company, POB 5038, Salinas CA 93915
Brinker Orsetti Seed Co., 2339 A Technology Parkway, Hollister CA 95023-2513.
Ferry-Morse Seed Co. POB 4938, 555 Codoni Ave. Modesto, CA 95352
Harris Moran Seed Co. 3670 Buffalo Rd. Rochester, NY 14624
Johnny's Selected Seeds, Foss Hill Rd. Albion, ME 04910
La Marche Seeds International, POB 190, Dixon, CA 95620
Liberty Seed Co. POB 806, New Philadelphia OH 44663
Nunhems Zaden, Canners Seed Corp. 221 E. Main St., Lewisville, ID 83431
Petoseed Co. Inc. POB 4206, Saticoy, CA 93304
Rijk Zwaan, Inc. 35 Harmony Rd. Warren, NJ 07060
Stokes Seeds Inc. POB 548, Buffalo, NY 14240
Vilmorin Inc. POB 707, Empire, CA 95319
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
Sandy peats and mucks, deep black sandy loams and loams are the most
suitable types of soil. Good moisture-holding capacity with good drainage is
important especially for heading types. Soils that compact easily, or are
compacted can adversely affect head lettuce growth. For successful head
lettuce production, soils should be managed to reduce compaction as much as
possible.
SOIL TEMPERATURE
Germination occurs at as low as 40 F and may not occur at temperatures
of 90 F and over unless irrigation is used to cool the soil. Crop growth is
usually good between 61 and 65 F.
SEED
Lettuce seed numbers approximately 400,000 per pound. Use only mosaic-
indexed seed from a reliable seed source.
For direct field seeding l/4 to l/2 lb/acre is required when a precision
seeder is used with unpelleted seed. Pelleting greatly improves precision
planting and reduces thinning costs. Advances in priming and coatings can
improve stand establishment under adverse conditions. Consult your seed
dealer about the availability of primed seed.
SEED TREATMENT
Use only fungicide treated seed. Seed is available pelletized with
various types of coatings. Pelletized seeds are available in which the seed
is vigorized, or conditioned, so that it germinates rapidly even under high
temperatures. Pelletizing facilitates precision seeding in the field. The
lighter coatings are preferred.
FERTILIZER
A soil test is the most accurate guide to fertilizer requirements. The
following recommendations are general guidelines.
For the early crop, band 2 inches to the side and 2 inches below the
planting depth the following:
Nitrogen: 75-100 (N) lb/acre for heading types developed for California
production. Use l50-l75 lb/A for Summertime and Ithaca grown on mineral
soils, and for leaf lettuces planted at 6-9 inches in-row spacings.
Phosphate: 150-200 (P2 O5) lb/acre.
Potash: 60-200 (K2 O) lb/acre
pH: Add lime if below 6.0
Slightly less nitrogen and phosphorus is required for the later plant-
ings of June and early July.
PRECISION SEEDING
Head lettuce is most commonly direct seeded in the field. Some transp-
lanting with "leaf" types is again becomming popular.
Present recommendations are to use coated seed. A single coated seed
placed every 2 to 3 in., or two seeds spaced 1 in. apart every 12 inches, has
worked very well. Direct-seeded plants should be thinned when two or three
true leaves have formed. Delaying thinning can result in plants that are left
to be disturbed or damaged, resulting in uneven harvest.
Raised beds are ideal for lettuce production. They help prevent damage
from soil compaction and flooding. This is especially important for the
varieties Summertime and Ithaca. Raised beds also improve air flow around the
plants resulting in reduced disease incidence.
TRANSPLANT PRODUCTION AND TRANSPLANTING
For transplant production, one-quarter of a pound of seed will supply
sufficient seedlings to transplant one acre.
The earliest seedings are started in flats in greenhouses in early Feb-
ruary. The seedlings are then transferred into other flats or modular trays
allowing 1-1 1/2 square inches per plant and are planted out as soon as the
fields can be prepared. Transplants put out early will benefit from a starter
solution high in phosphate. Spacing between rows is 14-18 in. with 11- 13 in.
between plants.
IRRIGATION
Lettuce requires frequent irrigations. As many as 8-10 irrigations and
10-12 inches of water per acre may be necessary depending on seasonal varia-
tion, variety and planting date.
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 AND STORAGE
Yields of crisphead lettuce are approximately 600-800 cartons per acre,
bibb and leaf lettuce approximately 800-1200 cartons per acre and romain
approximately 900-1000 cartons per acre (note container sizes and weights
under PACKAGING, below).
Harvest is done by hand, and the crop packed into cartons in the field.
Keep the leafy items clean, and free of soil and mud. A stronger bitter taste
and toughness develops if harvest is delayed or if crop is over- mature, and
then the product becomes unmarketable. Cool product as quickly as possible
using vacuum cooling.
Lettuce is extremely perishable and needs to be handled delicately, and
marketed rapidly. Lettuce may be held temporarily at 32 F and 90-95% relative
humidity for several days.
Head lettuce is harvested when the heads are of good size (about 2
lbs.), well formed and solid. If the plants are wet with rain or dew the
leaves are more brittle and break more easily. Leave 3 undamaged wrapper
leaves on each head. Put 24 heads in rigid cardboard containers in the field
and avoid bruising. Grade heads according to size, pack in cartons (vacuum
cooling is mandatory) for long shipments. Leaf, butterhead and cos types are
cut, trimmed and tied into compact bundles before placing in cartons.
STORAGE (quoted from USDA Ag. Handbook #66):
Hold lettuce at 32 F and 98 to 100 % relative humidity. Lettuce should
be precooled to 34 F soon after harvest and stored at 32F and 98 to 100 %
relative humidity for retention of quality and shelf life. Precooling is
commonly done by vacuum cooling because it is more effective and rapid that
hydrocooling. Also, since most head lettuce is field packed in corrugated
cartons, vacuum cooling is more suitable. For vacuum cooling, containers and
film wraps should be perforated or readily permeable to water vapor. To aid
vacuum cooling, clean water is sprinkled on the heads of lettuce prior to
carton closure if they are dry and warmer than 75 F. Thorough precooling is
essential because mechanically refrigerated rail cars or trucks do not have
enough cooling capacity to cool warm lettuce during transit.
Lettuce is highly perishable and deteriorates rapidly with increasing
temperature. The respiration rate increases greatly storage life decreases
concomitantly as the storage temperature increases over the temperature range
from 32 to 75 F. Leaf lettuce respires at about twice the rate of head
lettuce. At 32 F, head lettuce can be held in good condition for 2 to 3
weeks, the time period depending on maturity, quality, and handling condition
of the lettuce at harvest. The storage life at 38 F is only about half at
that at 32 F.
Lettuce is easily damaged by freezing, so all parts of the storage room
must be kept above the highest freezing point of lettuce (31.6 F).
Controlled atmosphere is of limited benefit to the storage quality of
lettuce. Low oxygen levels of 1 to 8 % can reduce russet spotting in sus-
ceptible lots. A 3 percent oxygen and 1.5 % carbon dioxide atmosphere
maintains the appearance of lettuce and inhibits pink rib and butt discolo-
ration better than air, but the effect is not noticeable after the lettuce is
held at 50 F in air for 5 days. Oxygen below 1 % is injurious, as is carbon
dioxide above 2.5 percent. High carbon dioxide levels cause brown stain,
which may develop after lettuce is transferred to 50 F air. Brown stain
caused by high carbon dioxide is intensified when oxygen is reduced to 2 to 3
%, but the degree differs with cultivar. If lettuce needs to be in transit
over-seas for a month, an atmosphere of 2 % carbon dioxide and 3 % oxygen is
recommended, because the reduction in decay achieved by 2 % carbon dioxide
outweighs the danger of injury.
Lettuce should be held at high relative humidity, 98 to 100%. Film
liners or individual polyethylene head wraps are desirable for attaining high
relative humidity; however they should be perforated or be permeable to
maintain a non-injurious atmosphere and to avoid 100 % relative humidity on
removal from storage. Romaine and leaf lettuce appear to tolerate a slightly
higher carbon dioxide level when packaged than head lettuce.
Russet spotting, which occasionally causes serious losses, is usually
not a problem at temperatures below 36 F. Lettuce should not be stored with
apples, pears, cantaloupes, or other products that give off ethylene, as this
gas increases russet spotting. Hard heads are more susceptible to this
disorder than firm lettuce. Storage in a low-oxygen atmosphere (1 to 8%) is
very effective in controlling russet spotting.
soft rot, the most serious disease of lettuce, often starts on bruised
leaves, but it is much less serious at 32 F than at higher temperatures.
Tipburn is also a major market disease of lettuce. It is of field origin, but
occasionally increases in severity after harvest.
PACKAGING
All packaging is done prior to vacuum cooling. Iceberg or head lettuce
may be closely trimmed and wrapped in film. Polyethylene films are most
common but new PVC films maintain freshness longer. PVC films are also easier
to wrap and result in a neater wrapping.
Iceberg lettuce: commonly packaged in 43-48 lb., 24 count, cartons.
Boston lettuce: commonly packaged in 20 lb. 1-1/9 bushel wirebound
crates.
Romaine lettuce: commonly packaged in 23 lb. l-l/9 bushel wirebound
crates or 24 count cartons.
Leaf lettuce: commonly packaged in 20-25 lb., cartons and wirebound
crates, 24 count; or, 13 lb. cartons.
Bibb lettuce: commonly packaged in 10 lb. cartons.
Greenhouse lettuce: commonly packaged in 10 lb. wood baskets or cartons.
PEST CONTROL FOR LETTUCE
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
Direct-seeded lettuce requires a couple of cultivations and a hand
thinning/weeding, whereas transplanted lettuce matures in 45 days following 1
or 2 cultivations with a minor hand weeding.
______________________________________________________________________________
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
preparation or preemergence crops listed on the label. Consult label
for specific rates, times of application, and perennial species con-
trolled. 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 produc-
tion of 3 amino acids and protein synthesis.)
______________________________________________________________________________
PREPLANT, PREEMERGENCE, AND POSTEMERGENCE
Weed Treatment Active Ingredient Per Acre and Application Comments
------------------------------------------------------------------------------
benefin 1.1 to 1.5 lb ai/A
Balan
(direct seeded lettuce only)
Apply from 10 weeks to immediately before planting and incorporate
within 8 hours by cross-disking or by using a PTO rotary tiller. May
be applied through center pivot and lateral move irrigation systems.
Spray only once and avoid overlapping. Consult label for planting
sensitive crops within 10 to 12 months. Control of many broadleaf weeds
is weak. (Inhibits mitosis, both in shoots and roots).
------------------------------------------------------------------------
bensulide 5 to 6 lb ai/A
Prefar
Apply preplant and incorporate in top 1 to 2 inches of soil by cross-
disking or using a PTO rotary tiller. Also may be applied preemergence
soon after planting before crop and weeds begin germination and activat-
ed with 1 inch overhead moisture. Sometimes the first flush of weeds
must be controlled with cultivation before herbicide begins to control
grass. Consult label for planting sensitive crops within 18 months. Do
not apply more than 1 time per year. Primarily a grass herbicide.
(Inhibits roots of seedlings).
------------------------------------------------------------------------
pronamide 1.0 to 2 lb ai/A
Kerb
(direct-seeded and
transplant lettuce,
endive and escarole)
Registration subject to cancellation; use existing supplies before label
is withdrawn. Restricted use pesticide. Apply preplant and incorporate
thoroughly by mixing in top 2 to 3 inches of soil or apply preemergence
at or soon after planting and activate with surface moisture to reduce
loss of herbicide. Consult label for partial list of sensitive varieties
and for planting sensitive crops within 12 months. Do not apply within
35 days of harvest. Primarily a grass herbicide. (Inhibits mitosis).
------------------------------------------------------------------------
cycloate 2 to 3 lb ai/A
Ro-Neet
In Washington, a special local needs (SLN WA-930019) is available.
Apply preplant to soil dry enough for thorough mixing and incorporate 2
to 3 inches deep immediately by cross-disking or using a rotary tiller.
Use on mineral soils only. Seed may be planted immediately. (Inhibits
shoot growth).
------------------------------------------------------------------------
phenmedipham 0.5 to 1.0 lb ai/A
Spin-Aid
Apply any time when lettuce are past 4-6 leaf stage and before weeds are
at the 2-leaf stage. Avoid applications when weather conditions may
change rapidly from cool and cloudy to warm and sunny days, or when
lettuce are stressed from insect, disease, disease, or cultivation in-
jury. Tip burn or temporary growth retardation and chlorosis may occur,
although plants usually recover within 10 days. Do not apply within 60
days of harvest. Avoid diluting herbicide more than one quart/7 g water
in spray tank as this can cause precipitation of the chemical. (Inhib-
its photosynthesis).
------------------------------------------------------------------------
sethoxydim 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 15 days of spinach and
leaf lettuce harvest or 30 days for head lettuce, nor exceed 3 pints/A
per season. Avoid applications when temperatures exceed 90 F or when
relative humidity exceeds 60%. (Inhibits fatty acid production, cell
membranes, and new growth.)
______________________________________________________________________________
______________________________________________________________________________
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, primarily Metasystox-R - 0.5 lb
Green peach aphid (Head lettuce only)
Myzus persicae
Phosdrin - 0.25 to 0.5 lb
Yellowish, pink to pale green
plant lice. diazinon - 0.5 lb
malathion - 1 to 2 lb
Lannate - 0.45 to 0.9 lb
dimethoate - 0.25 lb
Di-Syston - 1 to 2 lb
endosulfan - 0.75 to 1 lb
(Remove outside leaves of
head lettuce at harvest)
Orthene - 0.5 to 1.0 lb
(Crisp head lettuce only)
diatect - 1 to 3 lb
formulation
Pyrellin - 1 to 2 pt
---------------------------------------------------------------------------
Lettuce root aphid Di-Syston - 1 to 2 lb
Pemphigus bursarius
Grayish-green mealy aphids on roots.
---------------------------------------------------------------------------
Loopers, including methoxychlor - 1 to 2.25 lb
Alfalfa looper
Autographa californica Phosdrin - 0.5 to 1 lb
Worms are slender, dark olive Bacillus thuringiensis
green with paler head. They're 1 to 2 qt. Use a spreader-
marked with three dark stripes sticker to enhance control.
and move in a looping manner. 0.25 to 0.75 lb
Bacillus thuringiensis may be Apply at egg hatch.
combined with malathion for Thorough underleaf coverage
both worm and aphid control. essential for best results.
Check label for registered uses
of the new, improved strains of Lannate - 0.45 to 0.9 lb
B. thuringiensis.
endosulfan - 0.75 to 1.0 lb
(Remove outside leaves of head
lettuce at harvest)
malathion - 2.0 lb
permethrin - 0.05 to 0.1 lb
(Head lettuce only)
Orthene 75S - 0.5 to 1 lb
- crisp head lettuce only.
Cypermethrin - 0.025 to 0.10 lb
(Cymbush, Ammo). Head lettuce
only. Do not apply more than 0.6
lb ai per acre per crop season.
diatect - 1 to 3 lb formulation
Pyrellin - 1 to 2 pt
Asana - 0.03 to 0.05 lb
---------------------------------------------------------------------------
Cutworms and Armyworms Orthene - 1.0 lb Use only for
Several species Armyworm on crisp head lettuce.
Red, brown, green worms. Feed trichlorfon - 1 lb
on stems and leaves. Usually
in soil during the day. carbaryl - 1 to 2 lb
Lannate - 0.45 to 0.9 lb
Beet armyworm only.
Phosdrin - 0.5 to 1 lb
Climbing cutworms only.
permethrin - 0.1 to 0.2 lb
Use only for Beet Armyworm
on head lettuce.
Bacillus thuringiensis
1 to 2 qt
Cypermethrin - 0.025 to 0.10 lb
(Cymbush, Ammo). Head lettuce
only. Do not apply more than
0.6 lb ai per acre per crop
season.
Larvin - 0.4 to 0.75 lb
---------------------------------------------------------------------------
Slugs Metaldehyde baits.
Several species
Land mollusks that feed on
foliage and leave slime trails.
---------------------------------------------------------------------------
Cucumber beetles, diazinon - 0.25 to 0.375 lb
including Western spotted
cucumber beetle carbaryl - 1 lb
Diabrotica undecimpunctata
Yellowish-green, black-spotted Cypermethrin - 0.025 to 0.10 lb
beetle common to western Oregon.
Attack seedlings and feed on foliage. Pyrellin - 1 to 2 pt
---------------------------------------------------------------------------
Wireworms diazinon - 3 to 4 lb
Limonius spp.
Telone II - preplant
Brown, jointed larvae of click
beetles, kill young plants, Telone C-17 - preplant
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.
LETTUCE -- ANTHRACNOSE
Cause: Marssonina panattoniana, a fungus. This disease overwinters on crop
refuse.
Symptoms: Small, dead, brown spots appear on the leaves. The spots' centers
often fall out leaving black-margined, shothole spots. The spots progress from
the older leaves to the inner younger leaves. The outer leaves often break off
and blow away with the wind. The disease is important only during prolonged
periods of wet weather when it may cause heavy losses.
~Control:
1. Sanitary measures taken to reduce crop refuse assist in control. Deep
plowing and cultivating under lettuce parts are suggested. When grown in
greenhouses, soil should be sterilized by steam if available.
2. Practice crop rotation.
3. If only a small number of infections occur, remove affected plants as soon
as spots are visible together with any old dead leaves.
---------------------------------------------------------------------------
LETTUCE -- ASTER YELLOWS
Cause: A mycoplasmalike organism (MLO) virus transmitted by several leafhop-
pers.
Symptoms: The first symptoms of aster yellows are blanching and chlorosis in
the young heart leaves. Center leaves fail to develop normally and may appear
as short, thickened stubs in the center of the plants. Pink-to-tan latex
deposits collect on the affected leaves. In plants which are infected late in
the season the only symptoms are latex deposits within the head. In general,
infected plants are stunted, fail to "head," and are worthless for market.
~Control: Aster yellows has a wide host range. The elimination of weeds in
areas surrounding the lettuce planting will be helpful. Partial control may
be obtained by controlling the leafhopper vectors. Shaded plants are avoided
by leafhoppers.
---------------------------------------------------------------------------
LETTUCE -- (BEET) WESTERN YELLOWS
Cause: Beet western yellows virus, an increasingly significant pathogen in
western Oregon. The principal vector is the green peach aphid, Myzus
persicae, although other aphid vectors are likely. After acquiring the virus
from infected plants, aphids may retain for life the ability to transmit
virus. An enormous number of crop and weed species are susceptible to this
virus; thus the natural inoculum reservoir is hardly avoidable. Crop plants
commonly infected in western Oregon include beets (table and sugar), broccoli,
most clover species, mustard, lettuce, pea, radish, spinach, Swiss chard, and
turnip. Weed species commonly infected in western Oregon include burdock,
Canada thistle, cutleaf geranium, dog fennel, groundsel, pigweed, redstem
filaree, weedy clovers, and wild mustard.
Symptoms: Leaves turn yellow prematurely, typically beginning at the margins
and progressing inward, with veins and midribs tending to remain green. The
oldest leaves tend to become yellow first, with upward progression of yellows
symptoms, resulting in reduced and abnormal growth (i.e., unmarketable).
~Control: `Salinas' is tolerant. Attempts are underway to identify other
lettuce cultivars and breeding lines that are both suitable to the Pacific
Northwest and resistant to this virus. No other control measures are consid-
ered practicable.
-----------------------------------------------------------------------------
LETTUCE -- BIG VEIN
Cause: A soilborne virus transmitted by the fungus Olpidium brassicae.
Symptoms: Leaf veins appear decidedly larger because of clear areas along the
veins. Leaves may be puckered and mottled. Heads fail to size up. Often only a
rosette of leaves, but no head forms. Low temperatures favor the disease it is
evident in early and late crops much more than in midsummer crops.
~Control: On badly infested land, practice long rotations. Select land not
previously planted to lettuce if possible. Removing crop residue, rather than
working it into the soil, will prevent increase of the disease.
---------------------------------------------------------------------------
LETTUCE -- BOTTOM ROT
Cause: Rhizoctonia solani, a fungus. This disease is widespread occurring most
often on muck soil. It commonly attacks the `Big Boston' types of head
lettuce.
Symptoms: The disease appears after the plants have developed heads that are
approaching maturity. Clear cut necrotic spots appear on the stems and midribs
of the lower leaves and may enlarge over the entire stem. A brown exudate
appears on the surface of the spots, and infection continues to produce sunken
brown spots. The fungus may advance through the leaf blade until the entire
head is destroyed. Brown sclerotia develop near the axils of the leaves, and
the fungus may produce a noticeable network of growth around the head. The
head becomes slimy and dries up to a blackened mummy. Bacterial soft rot often
follows bottom rot invasion.
~Control:
1. Use well-drained soil or raised beds.
2. Rotate with nonsusceptible crops such as sweet corn or onions where
practical to do so.
3. Application of Ronilan for drop disease has also controlled bottom rot in
Washington trials.
4. Rovral controls bottom rot. See lettuce drop for instructions.
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LETTUCE -- DAMPING-OFF
Chemical control: Where Pythium sp. are a problem, use Ridomil 2E as a
broadcast or 7-inch band application in 20 to 50 gal of water at the rate of 4
to 8 pt/A for broadcast application. Bank application rates may be calculated
from a table provided on the label depending on band width, row spacing, etc.
Broadcast applications may be incorporated to a depth of 2 inches. If plant-
ings are made on beds, broadcast and incorporate before forming beds. (Head
lettuce only.)
Or treat seed with Anchor flowable at 1.5 fl oz/cwt of seed.
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LETTUCE -- DOWNY MILDEW
Cause: Bremia lactucae, a fungus. The fungus overwinters on wild hosts and
weeds. It is serious whenever outdoor winter crops are grown as well as in
greenhouses.
Symptoms: Light green or yellowish areas on the upper surface of the leaves
are matched by downy patches on the undersurface. Affected portions turn brown
and the leaves die. Older leaves are attacked first. The disease is worse in
periods of damp foggy weather and at low temperatures between 43and 53 F.
~Control:
1. Use thorough cultivation practices, particularly controlling weeds in the
vicinity, as many weeds are wild hosts.
2. Use resistant strains of lettuce, such as those developed in the Imperial
Valley. The following lettuce varieties are resistant to strains of downy
mildew as noted: `Bullseye' (II, III), `Target' (I, III), `Dynasty' (I),
`Bounty' (I), `Alpine' (I), and `Salinas' (I).
3. A copper-lime dust has been beneficial in greenhouses or in seedling beds,
but is seldom used in the field.
4. The cos variety `Valmarie' is tolerant.
5. Apply fosetyl-Al (Aliette) at 1.6 to 4.0 lb ai/A. Do not apply in less
than 15 gal water/A. Do not apply within 7 days of harvest.
6. Apply maneb at 1.2 to 1.6 lb ai/A. Do not apply more than 9.6 lb
ai/A/season. Do not apply within 10 days of harvest. Remove residues by
stripping and trimming.
7. Spray with fixed copper. Several formulations and products are available.
Check product label for rates.
8. Application of Ridomil for pythium control (see damping-off), offers some
control of downy mildew on young plants. To minimize the development of fungi
resistant to Ridomil, do not make foliar application if Ridomil was applied at
planting.
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LETTUCE -- DROP OR WATERY SOFT ROT
Cause: Sclerotinia sclerotiorum, a fungus. This disease survives the winter on
old lettuce refuse on the ground and as sclerotia in the soil.
The disease has two phases--the damping-off phase, attacking the seedlings,
and the important field phase known as "drop," which causes a watery soft rot.
It is severe whenever lettuce is grown under cool moist conditions.
Symptoms: Under moist conditions, the outer leaves wilt and there is a slimy
rot of the plant. A cottony fungus growth appears on the stem near the soil
level. The drop phase appears in midsummer or later following a wilting of the
leaves, beginning with the oldest leaves and continuing until the plant
collapses. The cottony fungus growth precedes this wilting stage. Hard
sclerotia develop throughout the diseased portion of the plant.
~Control:
1. Use well-drained land and avoid crowding plants in the field.
2. Remove old plant trash from previous crops where possible.
3. As many other vegetable crops are susceptible, rotation will usually not
solve the problem.
4. In irrigated areas, flooding the soil when the ground is not in produc-
tion helps to reduce sclerotia.
Spray (all lettuce) - Apply 1 to 2 lb Ronilan 50 WP, or 1 to 2 pt/A of Ronilan
FL in not less than 100 gal water/A. Apply within 2 days of thinning or 7- to
10- days of transplanting. Up to two more applications can be made at 14-day
intervals on direct seeded lettuce and one more on transplants. Do not apply
within 28 days of harvest.
Spray (all lettuce)--Apply 1.5 to 2.0 lb Rovral 50 WP in 50 to 100 gal water/A
by ground. Apply at the three leaf stage of growth and again 10 days later. A
third application can be made 10 days later if disease pressure persists.
Residues:
Ronilan - Do not apply more than 1 lb actual/A per application. Do not apply
within 28 days of harvest. Do not apply more than 3 lb ai/A in one season.
Rovral - Do not apply more than 1 lb ai/A per application. Do not apply within
14 days of harvest or more than three times per season. See label for
rotation restrictions.
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LETTUCE -- MOSAIC
Cause: A virus transmitted by seed and by the green peach aphid.
Symptoms: In the young plant the first symptoms are upward rolling of the
seedling leaves on the long axis and the first true leaf is irregular in shape
and slightly lobed. These symptoms are followed by vein clearing and bronzing.
The bronzing is caused by necrotic flecking of the leaf blade, especially
along the veinlets symptom expression varies with variety and climatic
factors.
In older plants the mottle symptom is absent or indistinct. In half-grown
plants, the whole plant is severely stunted and a dull-green to slightly
yellow color. The tip of the outer leaves is rolled downward giving the plants
a wilted appearance although the leaves may be turgid. The midribs of these
stunted plants protrude abnormally on the underside of the leaf and give the
lower portion of the heads a ribby appearance.
~Control:
1. Disease-free seed is the best means of control. Avoid planting varieties
of lettuce that are not tested for mosaic in the same field with tested
material.
2. Control weeds, particularly wild lettuce in the vicinity of the planting.
3. There are no resistant varieties yet, but breeders are hopeful of produc-
ing resistance soon.
4. Remove diseased plants whenever apparent.
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LETTUCE -- RED RIB (Rib Blight)
Cause: Unknown, but is believed to be of physiological origin. Tests have not
been able to associate red rib with soil types, pH, fertilizing practices,
etc.
Symptoms: Brownish-red spots on the leaves, mainly on the ribs, which enlarge
to become fairly wide bands--up to 2 inches by 3 to 4 inches long. The
discolored streaks or bands are diffuse, not sharp edged. The disorder may
affect one or two ribs of the outside leaves, but often the discoloration
continues through to the inner leaves from these points. The larger bands of
affected tissue may crack, allowing the entrance of rot organisms. The
varieties `Ithaca' and `Summertime' are tolerant of this condition.
~Control: Other states report that the variety `Great Lakes' and other
California varieties are frequently affected. The disorder was first reported
in Oregon in 1956, from the Eugene area, where a 2-acre field of the `Great
Lakes' variety was almost 100 percent affected with subsequent severe loss to
the grower. Harvest promptly. Several harvests may be necessary to remove
heads before disorder appears.
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LETTUCE -- SEED TREATMENT
Aids in control of seed decay and damping-off:
Thiram 4 oz ai/100 lb seed. Considered to be a nonfood use.
Where Pythiuim is a problem, use Anchor flowable at 1.5 fl oz/cwt seed.
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LETTUCE -- TIP BURN
Cause: Physiological disorder. All lettuce varieties grown in the Pacific
Northwest are susceptible to some degree to tip burn. Considerable difference
between varieties is recognized. The precise conditions under which tip burn
develops have not been identified. At least five environmental conditions have
been reported to favor the development of the disorder. All of these have an
effect on calcium uptake or distribution within the plant: 1) High relative
humidity combined with high temperatures, particularly night temperatures
above 65 F during head development. 2) Conditions that favor rapid succulent
growth such as abundant moisture and an abundant supply of plant nutrients. 3)
An inadequate or fluctuating water supply as the crop matures. 4) Low soil and
air temperatures during early development followed by a period of high
temperatures with low humidity as the crop nears maturity. 5) An imbalance in
the mineral nutrition of the crop, particularly as affecting calcium. Exces-
sively high levels of potassium and magnesium or high applications of ammonium
nitrogen have been reported to predispose lettuce to tip burn, particularly
where soils are low in calcium to begin with.
Symptoms: The initial symptoms of tip burn are small, dark-brown spots along
the margins of the interior or exterior head leaves. These spots later merge
together, and the entire margin becomes brown and necrotic. Tip burn is more
serious when it occurs on the internal leaves of the head. Internally, the
dark-brown necrotic leaves make the heads unmarketable and cannot be detected
and eliminated from the pack by the harvest crews. The internal necrotic areas
are ideal sites for the development of secondary organisms, particularly
various rot organisms that cause a watery breakdown of the tissue, commonly
known as slime. Usually only a few leaves of the head are affected with tip
burn.
~Control: There is no specific control for this disorder. Calcium chloride
treatments showed some effects in test plots but no effect in field plots in
reducing the disease. The more resistant varieties should be used. The
varieties `Ithaca' and `Summertime' are recommended for main season produc-
tion. It is important to maintain adequate calcium levels in the soil and to
manage fertilizer and irrigation programs so as to provide even growth
throughout the plant's life. Soil samples should show adequate base saturation
and adequate levels of calcium. Nitrogen forms may be important with nitrate
forms being preferred over ammonium forms. Lettuce should be harvested at
optimum maturity since tip burn tends to be more serious on overmature
lettuce. Under Oregon conditions, all California varieties are susceptible.
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LETTUCE -- VARNISH SPOT
Cause: A bacterium, Pseudomonas cichorii, which can survive in the soil for
some time after the lettuce crop is removed.
Symptoms: Dark-brown, firm, necrotic spots a few millimeters in diameter occur
on leaves and petioles of lettuce several layers within the lettuce head.
Since outer layers of leaves are rarely affected, it is usually impossible to
detect the disease without destroying the head.
~Control: Little information is available on control. Several years of rotation
out of lettuce and minimizing overhead irrigation during the last 3 weeks
before harvest may be helpful.
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LETTUCE -- BLACK MARGIN BURN
Cause: A bacterium Pseudomonas marginalis which causes a black tip burning.
Prevalent in cool moist conditions.
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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 or questions
to your County Extension Agent or Dr. N. S.
Mansour, Department of Horticulture, Oregon State
University, Corvallis, OR 9733l.
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