Peas (Green or English)
Tim Miller
Revised December 17, 2008
PEAS (GREEN OR ENGLISH)—General Weed Management Strategy
Peas are drilled in closely spaced rows early in spring, which limits weed emergence and species diversity. Most growers apply herbicides to suppress or eliminate weed competition or potential contamination of harvested product. Subsequent crop rotations during the same season limit herbicide choices to those exhibiting brief soil residuals.
PEAS (GREEN OR ENGLISH)—Stale Seedbed Method
Refer to “Stale Seedbeds” in the Vegetables section of this Handbook for information on the following options.
•  flaming
•  glyphosate
•  paraquat
•  pelargonic acid
•  carfentrazone
PEAS (GREEN OR ENGLISH)—Preplant Incorporated
•  trifluralin (several trade names)
Rate  0.5 to 0.75 lb ai/A
Time  Apply preplant, and incorporate 1 to 2 inches deep within 24 hr by cross-disking, rototilling, or cross-tilling with a field cultivator.
Remarks  Spray only once per season. Avoid overlapping. Use lower rate on coarse soils. Peas have been stunted when maximum labeled rates were applied uniformly in fields with slight variations in soil type. Consult label for planting sensitive crops within 12 mo.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  triallate (Far-Go)
Rate  1.25 to 1.5 lb ai/A (2.5 to 3 pints/A)
Time  Apply within 3 wk of planting. Incorporate immediately using a disk or spike-tooth harrow. 
Remarks  Controls wild oat and annual ryegrass.
Site of action  Group 8: lipid synthesis inhibitor but not an ACCase inhibitor
Chemical family  Thiocarbamate
•  triallate (Far-Go) +
•  trifluralin
Rate  1.25 lb ai/A + 0.375 lb ai/A, respectively
Time  Apply within 3 wk of planting. Incorporate within 24 hr with disk or spike-tooth harrow.
Remarks  Provides better control of wild oat at a lower rate of trifluralin.
Caution  Do not use foliage from treated peas for feed or forage. Peas may show leaf crinkling and delayed maturity, particularly on heavy soils.
Site of action  (triallate) Group 8: lipid synthesis inhibitor but not an ACCase inhibitor; (trifluralin): Group 3: microtubule assembly inhibitor
Chemical family  (triallate) thiocarbamate; (trifluralin) dinitroaniline
•  triallate + trifluralin (Buckle)
Rate  10 to 12 lb/A granular
Remarks  Follow label directions and note comments above.
Site of action  (triallate) Group 8: lipid synthesis inhibitor but not an ACCase inhibitor; (trifluralin): Group 3: microtubule assembly inhibitor
Chemical family  (triallate) thiocarbamate; (trifluralin) dinitroaniline
•  imazethapyr (Pursuit)
Rate  Consult labels.
Time  Apply only once per year. Preharvest interval is 6 days for peas. See label about planting rotation crops. 
Remarks  Registered only in certain eastern Oregon and Washington counties and in Idaho.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Imidazolinone
•  pendimethalin (several trade names)
Rate  0.5 to 1.5 lb ai/A 
Time  Apply and incorporate up to 60 days before planting. Rate depends on soil texture. 
Remarks  Thoroughly mix previous crop residue into soil 4 to 6 inches before applying.
Caution  Do not apply more than once per season. Do not apply to peas, pea forage, pea silage, pea hay, or pea straw grown for livestock feed.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
PEAS (GREEN OR ENGLISH)—Preemergence Soil-applied
•  S-metolachlor (Dual Magnum)
Rate  0.95 to 1.91 lb ai/A
Time  Apply preemergence behind planter and activate with moisture.
Remarks  May delay maturity and/or reduce yields if soils are cold and wet after planting.
Caution  Preharvest interval is 120 days for hay. 
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  clomazone (Command 3ME)
Rate  0.5 lb ai/A (1.3 pints/A)
Time  Apply to soil before or after seeding but before crop emerges.
Remarks  See label for crop rotation restrictions and application requirements to avoid crop injury or vapor drift to sensitive plants. Some temporary chlorosis of green peas may occur. Avoid overlaps while spraying.
Caution  Do not mix or apply within 1,000 ft of landscapes, orchards, vegetable gardens, berry patches, or property lines to prevent chemical trespass. Evidence west of Cascades suggests that lower rates of 0.25 to 0.33 lb ai/A (11 to 14 fl oz/A) control susceptible weeds in early spring. Do not graze cover crops or harvest food or feed within 9 mo of application or allow livestock to graze on treated pea vines or vine trash.
Site of action  Group 13: inhibits DOXP synthase
Chemical family  Isoxazolidinone
•  metribuzin (several trade names)
Rate  0.25 to 0.38 lb ai/A (5.3 to 8.1 oz/A)
Time  Apply once per season soon after planting and incorporate with irrigation or cross-harrow to ensure uniformity within top 1 to 2 inches of soil.
Remarks  Adjust rates for soil texture and organic matter. Do not exceed 0.15 lb ai/A (3.2 oz/A) on wet soils. 
Caution  Restricted-use herbicide in Washington. Do not use on coarse, sandy, or shallow soils or on soils with less than 1.5% organic matter. Crop may be injured if heavy rain follows application. Do not apply more than 0.5 inch of irrigation within 1 mo after metribuzin to avoid crop injury. Experience is lacking in western Oregon; try small areas before treating large acreages. Crop may be injured if plants are stressed by cold weather, poor soil fertility, and disease or insect damage. Will not control weeds resistant to triazine (atrazine) herbicides. Grazing is permitted 40 days after treatment. Certify that pea variety, location, and irrigation conditions are listed on the product label you purchase.
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazinone
PEAS (GREEN OR ENGLISH)—Postemergence
•  MCPA (several trade names)
Rate  0.125 to 0.38 lb ae/A
Time  Apply postemergence to control small broadleaf weeds or prevent flowering in larger weeds such as nightshade when peas exceed 4 to 6 inches.
Remarks  Adjust rates for expected temperatures; see label.
Caution  Do not apply if temperature may exceed 90°F within 24 hr. Maintain spray pressure below 40 psi to minimize drift from target field. 
Site of action  Group 4: synthetic auxin
Chemical family  Phenoxy acetic acid
•  MCPB (Thistrol)
Rate  0.5 to 1.5 lb ae/A (2 to 6 pints/A)
Time  Apply at six- to twelve-node stage for peas and to Canada thistle during stem elongation but before 8 inches tall. Higher rate required during cool weather. 
Remarks  Prevents development of Canada thistle buds and contamination of harvested product. Some evidence exists that early-morning applications are safer to crop than afternoon applications.
Caution  Do not feed treated peas or vines to livestock. Do not spray when air exceeds 90°F or when peas are moisture stressed. 
Site of action  Group 4: synthetic auxin
Chemical family  Phenoxy acetic acid
•  metribuzin (several trade names)
Rate  0.09 to 0.25 lb ai/A (2 to 5.3 oz/A)
Time  Apply only once per season to susceptible broadleaf weeds less than 2 inches tall or wide.
Remarks  Do not apply more than 0.5 inch of irrigation within 1 mo after metribuzin applied or crop may be injured. In western Oregon, try small areas before treating large ones. Warm weather or tank-mixes with bentazon have caused injury west of Cascades. Preharvest interval is 50 days; grazing is permitted after 40 days. Ensure peas, location, or irrigation conditions are listed on product label. Special local needs label WA-040031 (only for Sencor herbicide) allows a shorter preharvest interval (40 days) in western Washington if Sencor rate is less than 0.2 lb ai/A (3.5 oz/A). 
Caution  Restricted-use herbicide in Washington. Do not apply to wet crop foliage or very moist soil surface. Do not apply within 3 days after cool, wet, or cloudy weather or within 24 hr of other pesticide applications (except tank-mixes specified on label) to minimize risk of crop injury. Do not use on coarse, sandy, or shallow soils or on soil with less than 1.5% organic matter.
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazinone
•  bentazon (Basagran)
Rate  0.75 to 1 lb ai/A (1.5 to 2 pints/A)
Time  Apply as pea tolerance increases as waxes develop on leaf surfaces.
Remarks  Crop age (three leaf pairs or four nodes), temperature, weather, and spray additives affect penetration through waxes into pea leaves. Small, newly emerged broadleaf weeds can be controlled in early spring at cool temperatures (75°F day, 55°F night) by adding a highly refined nonphytotoxic oil concentrate (see label). Temporary leaf symptoms may occur, but peas mature normally. Avoid conditions that enhance excessive penetration into pea leaves, such as temperatures over 80°F or application on a sunny day immediately after several cloudy days. 
Caution  Do not tank-mix with spray additives or pesticides except MCPA and MCPB (without crop oil). Preharvest interval is 30 days. Do not exceed 2 lb ai/A (4 pints/A) per season. 
Site of action  Group 6: photosystem II inhibitor
Chemical family  Benzothiadiazole
•  sethoxydim (Poast)
Rate  Consult label.
Time  Apply at optimum growth stage listed on label. 
Remarks  Identify susceptible grasses and add 2 pints/A nonphytotoxic crop oil concentrate to improve leaf absorption. Control often is erratic on grasses stunted or stressed from drought, high temperatures, or low fertility. Tolerant grasses include annual bluegrass and all fine fescues, but quackgrass can be suppressed.
Caution  Do not mix or apply with any other pesticide, additive, or fertilizer except as specified on label. Preharvest interval is 15 days. Do not exceed 0.75 lb ai/A (4 pints/A) per season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione 
•  quizalofop (Assure II)
Rate  0.04 to 0.08 lb ai/A
Time  Apply at optimum growth stage listed on label.
Remarks  Identify susceptible grasses, and add 4 quarts crop oil concentrate or 1 quart nonionic surfactant/100 gal of spray mix. Grass control may be reduced if applied immediately before or after a broadleaf herbicide.
Caution  Do not mix with or apply with any other pesticide except as specified on label. Do not apply to plants stressed from lack of moisture, cold, or injury from herbicides, insects, or disease. Preharvest interval is 30 days. Do not exceed 0.1 lb ai/A per season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Aryloxyphenoxy propionate
•  clethodim  (several trade names)
Rate  0.068 to 0.12 lb ai/A (9 to 16 oz/A on annual grasses; 12 to 16 oz/A on perennial grass weeds)
Time  Apply to actively growing grasses at recommended weed heights.
Remarks  Recommended surfactant is nonionic surfactant at 0.25%; do not add ammonium sulfate.
Caution  Do not exceed 32 fl oz/A/yr. Allow at least 14 days between applications. Preharvest interval is 30 days. 
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione

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