Postemergence

bromoxynil (Buctril, Broclean, Brox 2EC, or Buctril 4EC)

Idaho and east of the Cascades, dry bulb onions only

Rate 0.25 to 0.38 lb ai/a (1 to 1.5 pints/a) for Buctril, Broclean, and Brox 2EC. Use 0.25 to 0.375 lb ai/a (0.5 to 0.75 pints/a) for Buctril 4EC.

Time Apply in 50 to 70 gal water for thorough coverage when onions have two to five true leaves. Apply on sunny days when plants are dry and humidity is low.

Caution Do not ingest or inhale spray mist. Prevent contact with skin. Wear protective face shields, respirators, and coverall clothing over long-sleeved shirt and long pants. Do not apply west of the Cascades or when protective waxy cuticle on onion leaves may be thin or damaged. Do not add adjuvants. Injury can sometimes occur, even under ideal conditions. Read the label on precautions and restrictions.

Site of action Group 6: photosystem II inhibitor

Chemical family Nitrile

carfentrazone (Aim)

Rate Up to 0.031 lb ai/a (0.5 to 2 fl oz/a Aim EC) per application in at least 10 gal/a of finished spray

Time Apply (postemergence only) with hooded sprayer between rows of emerged crop.

Remarks See the table of approved uses on vegetable crops under "Selective Postemergence Applications" at the beginning of Section P. Vegetable Crops in this handbook. Hooded sprayers must prevent spray from reaching green stem tissue, foliage, blooms, or fruit of the crop. Do not use for preplant burndown on fields intended for bulb vegetables.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family Triazinone

clethodim (Select Max or Select 2EC)

Dry bulb onions, garlic, and shallots only

Rate Consult labels for information on dry bulb onion and shallots.

Time Apply to actively growing grass weeds, including annual bluegrass, at growth stage on label.

Remarks Carefully read label for adjuvant instructions and about effects of rain within 1 hour, applying other pesticides, or cultivation. Application should be made in a minimum of 20 gal of spray solution per acre. May be applied to onions and garlic using sprinkler irrigation systems. Do not apply using chemigation in ID, OR, and WA.

Caution Consult labels for maximum rates per application and season. Preharvest interval is 45 days for dry bulb onions, garlic, and shallots. Applications to dry bulb onions or shallots should be made in a minimum of 20 gal of spray solution per acre.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Cyclohexanedione

fluazifop (Fusilade DX)

Dry bulb onions only

Rate 0.125 to 0.188 lb ai/a (8 to 12 oz/a) depending on target weed species and growth stage.

Time Apply to actively growing grasses with 1% crop oil, or 0.25% nonionic surfactant. Results often are erratic on grasses stressed from lack of vigor, drought, high temperature, or low fertility. Do not apply more than 48 fl oz/a in total per season.

Remarks Identify grasses; adjust rates depending on susceptibility and stage of weed growth as label instructs. More mature grasses and quackgrass can be controlled but may require two applications. Annual bluegrass and all fine fescues resist treatment. Inhibits fatty acid production, cell membranes, and new growth.

Caution Preharvest interval is 45 days. Do not exceed 3 pints/a per year. Grazing is prohibited.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Aryloxyphenoxy propionate

fluroxypyr (Starane Ultra or Obtain EC)

Dry bulb onions only

Rate 0.125 lb ae/a (0.35 pints/a product)

Time Apply broadcast postemergence from the two true-leaf stage though the six-leaf stage. Weeds should be 4 to 8 inches tall.

Remarks SLN labels OR-080026, ID-080007, and WA-080008 (Starane Ultra) for control of kochia, volunteer potatoes, common purslane, and other susceptible broadleaf weeds. Adjuvants are not recommended. Heavy flushes of weeds can be controlled with two sequential applications at 10- to 14-day intervals. Do not exceed 0.7 pint/a, or two applications, per year.

Caution Crop injury may occur with some onion varieties. Do not broadcast after the six-leaf stage. Applications after the six-leaf stage should be made as a directed spray with drop nozzles (consult the label for the warning). Do not apply through any type of irrigation system. Preharvest interval is 42 days.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

paraquat (Gramoxone Inteon)

Rate 0.63 to 1 lb cation/a (2.5 to 4 pints/a)

Time Apply before, during, or after planting but before crop emerges, to control emerged weed seedlings only.

Remarks 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. Acts as contact; absorbs energy from photosynthesis, forming peroxides that disrupt living cells.

Caution A restricted-use herbicide. Do not ingest or inhale spray mist. Wear protective face shields, respirators, and clothes. Do not exceed 4 pints/a per season. Preharvest interval is 60 days.

Site of action Group 22: photosystem 1 electron diversion

Chemical family Bipyridilium

pendimethalin (Prowl H2O or Prowl 3.3EC)

Dry bulb onion and shallots, direct-seeded and transplanted

Rate 0.6 to 1.24 lb ai/a (1.5 to 3.0 pints/a Prowl H2O) or 0.74 to 1.49 lb ai/a (1.8 to 3.6 pints/a Prowl 3.3EC) depending on soil texture. May be applied at 1.42 to 1.9 lb ai/a (3 to 4 pints/a Prowl H2O) or 1.48 to 1.98 lb ai/a (3.6 to 4.8 pints/a Prowl 3.3EC) for dodder control on medium- and fine-textured soils in Oregon, Idaho, and Washington. The indicated rate is for all uses, regardless of application timing (delayed preemergence (Prowl H2O only) or postemergence).

Time Apply Prowl 3.3EC between the flag leaf to ninth true-leaf stage. DO NOT apply Prowl 3.3EC using chemigation at the dodder control rate. Do not irrigate in excess of 0.5 inch of water.

Remarks Prowl H2O and Prowl 3.3EC may be applied by ground, air, or chemigation (only to direct-seeded, transplanted dry bulb onions and shallots). May be applied through sprinkler irrigation systems (only to direct-seeded, transplanted onions and shallots). Follow all directions, special instructions, and precautions about chemigation in the spraying instructions section of the main labels. Adjust rates according to soil texture. Rain or overhead irrigation is needed within 10 days of application. Inhibits mitosis in shoots and in roots.

Caution Be aware of crop rotation restrictions, including those for sugar beet, winter wheat, and winter barley. Do not apply within 45 days before harvest. Do not exceed the maximum rate per season regardless of application timing (delayed preemergence or postemergence).

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

sethoxydim (Poast)

For dry bulb onion and green onions, garlic, leek, and shallots

Rate 0.19 to 0.28 lb ai/a (1 to 1.5 pints/a) depending on target grass species and growth stage

Time Apply at optimum growth stage as on label.

Remarks Identify susceptible grasses, and add 2 pints/a nonphytotoxic crop oil concentrate to improve leaf absorption. Results often are erratic if grasses are stressed from lack of vigor, drought, high temperature, or low fertility. Resistant grasses include annual bluegrass and all fine fescues, but quackgrass can be suppressed. Inhibits fatty acid production, cell membranes, and new growth. Do not exceed 4.5 pints/a per season.

Caution Preharvest interval is 30 days. Do not exceed 4.5 pints/a per season.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Cyclohexanedione

trifluralin (Treflan TR-10)

Dry bulb onions only

Rate 0.38 to 0.63 lb ai/a (3.75 to 6.26 lb/a broadcast rate)

Time Apply at layby as a directed spray to the soil between rows, and incorporate immediately with sweeps or rolling cultivators. Avoid applying directly to the tops or exposed bulbs of onion plants.

Remarks Use proportionately less when treating area between rows only. Inhibits mitosis in shoots and roots.

Caution Do not apply to soils with more than 3.5% organic matter, because effectiveness will be reduced. Do not apply preplant or preemergence. Preharvest interval is 60 days. Remove emerged weeds before applying. See label for planting sensitive crops within 12 months.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline