Preemergence, Delayed Preemergence, Early Postemergence

DCPA (Dacthal Flowable)

Onions [dry bulb onions, dry bulb shallots and green onions (green onions, leeks, spring onions or scallions, Japanese bunching onions, green shallots or green eschalots)]

Rate 4.5 to 10.5 lb ai/a (6 to 14 pints/a)

Time Apply after planting to soil surface before weeds germinate and onions emerge. A layby application can be made on onions either alone or in addition to a Dacthal Flowable preemergence treatment up to 14 weeks after planting at rates up to 14 pints/a on any soil type. Dacthal Flowable can be sprayed directly over transplants without injury.

Remarks Performs erratically west of the Cascades. In eastern Oregon and Washington, if overhead irrigation is not available, apply and shallowly incorporate herbicide with a nailboard. Rain after incorporation improves weed control. Preplant incorporation is not recommended for onions. Results improve with overhead irrigation immediately after application. Consult label for planting sensitive crops within 8 months. In sandy loam soils, a maximum preemergence rate of 10 pints/a is recommended. Where onion emergence is expected to be slow due to cold and wet soil condition, delay application until seed begins to germinate to reduce the risk of crop injury. Preplant incorporation is not recommended for onions. Inhibits mitosis.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Phthalic acid

dimethenamid-P (Outlook)

Onions (dry bulb and green), garlic, and dry bulb shallots

Rate 0.56 to 0.84 lb ai/a (12 to 18 fl oz/a) on coarse soils and 0.84 to 0.98 lb ai/a (18 to 21 fl oz/a) in medium-texture or fine soils. May be applied in a single application. Do not exceed 21 fl oz/a per season.

Time Apply postemergence from the two true-leaf stage until at least 30 days before harvest.

Remarks Split applications of 10 to 14 oz/a followed by 7 to 14 oz/a are permitted but cannot exceed a total of 21 oz/a. If split applications are made, maintain a minimum of 14 days between sequential applications. Refer to the EPA-approved labels for specific application methods and requirements.

Caution Applications before the two true-leaf stage may significantly injure the crop. Aerial applications must leave a 150-ft untreated buffer between treatment area and endangered plant populations. Ground applications must use low-pressure nozzles that produce only medium to coarse or very coarse droplets and leave a 35-ft untreated buffer between treatment area and endangered plant populations.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

dimethenamid-P (Outlook)

Dry bulb onions (yellow only) applied through the irrigation drip system (OR and ID).

Rate 0.328 to 0.656 lb ai/a (7 to 14 fl oz/a) on medium to heavy soils. May be used in a single application up to 14 fl oz/a or in split applications of 7 to 14 fl oz/a followed by the remaining 7 to 14 fl oz/a in sequential applications. Do not exceed 21 fl oz/a per season.

Time Apply postemergence to onion with two fully developed true leaves but NOT later than six leaf stage.

Remarks When split application rate is >7 fl oz/a, separate sequential applications by at least 14 days. When split application rate is 7 fl oz/a or less, separate sequential applications by at least 7 days. Do not exceed a total of 21 oz/a per season or apply beyond the six leaf stage. For best results, dilute the herbicide in enough water to last for 10 to 12 hr of chemigation. Refer to the EPA SLN OR-160004 for OR (Malheur County only) and EPA SLN ID-160001 for ID (Ada, Canyon, Gem, Owyhee, Payette, and Washington Counties). DO NOT apply with any other pesticides, fertilizers, adjuvants, or other products. Refer to EPA-approved labels for specific application methods and requirements.

Caution Applications before the two true-leaf stage may significantly injure the crop. User must have the SLN label and the entire Outlook container label in possession at the time of pesticide application. Do not apply more than a cumulative maximum amount of 21 fl oz/a through drip tape chemigation and/or foliar spray in a single season.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

ethofumesate (Nortron SC, Ethotron SC)

Dry bulb onions and shallots only

Rate Preemergence: 0.5 to 1 lb ai/a (16 to 32 fl oz/a) depending on soil texture. Weed control diminishes in soils with fine texture or high organic matter. Postemergence: 0.5 lb ai/a (16 fl oz/a) with up to four evenly spaced sequential applications, with last application 28 to 32 days before harvest.

Time Apply after planting, and activate with at least 0.5 inch of water, or apply after crop emerges.

Remarks Do not use smaller than 50 mesh screen, and avoid overlaps, which may increase risk of crop injury. For postemergent applications, rain or irrigation within 6 hr after application may reduce weed control. On coarse soils; do not exceed 48 fl oz/a of product per season. On medium and fine textured soils; do not exceed 96 fl oz/a of product per season. For postemergence applications, do not retreat within 10 days. Do not apply more than 4 split applications per year.

Caution May cause temporary leaf fusion, distortion, and stunting when used as label directs and under normal growing conditions. If crop is lost due to unfavorable growth conditions after application, do not plant anything except sugar beets, table beets, onions, garlic, shallots, or ryegrass. If crop is lost due to unfavorable growth conditions following application of Nortron SC herbicide or tank mixes, do not replant with crops other than sugar beets, table beets, carrots, dry bulb onions, shallots, or ryegrass in treated land during the same year.

Site of action Group 16: unknown (but there is strong evidence that it interferes with biosynthesis of fatty acids and lipids in the newly developing shoot).

Chemical family Benzofuran

oxyfluorfen (GoalTender, Goal 2XL, or Galigan 2E, Galigan H2O)

Dry bulb onion, green onions (via sprinkler application)

Rate 0.12 to 0.25 lb ai/a (0.25 to 0.5 pint/a GoalTender and Galigan H2O) in direct-seeded and transplanted onions. The rate for Goal 2XL and Galigan 2E use 0.125 to 0.25 lb ai/a (0.5 to 1 pint/a).

Time Apply postemergence to onions with two fully developed true leaves, while broadleaf weeds have fewer than four true leaves. Goal applications are allowed on green onions through sprinkler irrigation systems (Special local needs label OR-020027). Read and precisely follow label instructions regarding irrigation interval and all chemigation specifications to minimize environmental hazards.

Remarks Multiple treatments may be required as new weeds emerge, but do not exceed 0.5 lb ai/a (maximum of 2.5 pints/a per use season). Use a clean sprayer and do not mix with oils, surfactants, or other agricultural chemicals. Apply when susceptible weeds are in the two- to four-leaf stage and actively growing. Acts as a selective contact herbicide that disrupts cell membranes.

Caution Do not apply to onions that are under any stress. Leaves may curl slightly, and young plants sometimes become prostrate on the soil surface for 1 to 2 days, but yields have not been reduced. Preharvest interval is 45 days. Goal damages some onion varieties more easily than others; "Walla Walla" sweet onions are very sensitive. Check with your seed supplier for information regarding the variety you wish to plant.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family Diphenylether

pendimethalin (Prowl H2O and various generic names)

Dry bulb onions and shallots only, direct-seeded or transplanted

Rate 0.475 to 1.42 lb ai/a (1 to 3 pints/a Prowl H2O) depending on soil texture.

Time Delayed preemergence for dry bulb onion only (after onion seed germinates but before it emerges); and after onions emerge (two- to nine-true-leaf stage). Delayed preemergence: apply Prowl H2O when 75% of dry bulb onion seed radicals have emerged. Determine radical status by digging onion seedlings at random locations in a field, and noting radical length. Plant onions at least 1 inch deep to mitigate risk of injury. Apply Prowl H2O as a broadcast treatment when dry bulb onions or dry bulb shallots are between the flag leaf to 9th true-leaf stage. Prowl H2O may be used at 3.0 to 4.0 pints per acre for dodder control on medium-texture and fine-texture soils. DO NOT apply Prowl H2O using chemigation at the dodder control rate. See restrictions and limitations on the label.

Remarks Prowl H2O is a selective delayed preemergence herbicide for controlling most annual grass weeds and certain broadleaf weeds as they germinate. Prowl H2O will not control established weeds. SLN labels are available for delayed preemergence for Prowl H2O (OR-060008, WA-070004, and ID-060009) from several grower associations in western and eastern Oregon, Washington, and Idaho. Adjust rates according to soil texture. Rain or overhead irrigation is needed within 10 days for activation. Inhibits mitosis, both in shoots and roots.

Caution Adjust rates according to soil texture. Do not apply preplant incorporated, or preplant. For use under SLN labels in OR, WA, and ID. Do not apply delayed preemergence through any type of irrigation system or by air. Be aware of crop-rotation restrictions, including for sugar beets, winter wheat, and winter barley. Do not exceed the maximum rate per acre, per crop season regardless of application timing.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

pendimethalin (Prowl H2O and various generic names)

Green onion crop subgroup: chives (fresh leaves), leeks, spring onions, scallions, Japanese bunching onions, green shallots, and green eschalots

Rate 0.95 lb ai/a (2 pints/a)

Time Preemergence, postemergence at two- to three-leaf stage, or as a split application.

Remarks Apply 2 pints/a per application. Two applications per season are allowed with 30 days between applications. Preharvest interval is 30 days.

Caution Onion seed must be covered with soil to prevent injury. Do not apply to soils with less than 3% organic matter.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

S-metolachlor (Dual Magnum)

Early postemergence for yellow nutsedge control in dry bulb onion; Oregon, Idaho, and Washington

Rate and Time Apply at two true-leaf stage of onions at 0.67 to 1.33 pints/a (0.64 to 1.27 lb ai/a). Another application of 0.67 to 1.33 pints/a may be made 21 or more days after the first, if needed, provided Dual Magnum was not applied preplant in fall.

Remarks Indemnified special local need labels OR-040009 and ID-9900016 are available at farmassist.com. The Washington SLN label (WA-990023) is distributed only by the Walla Walla Sweet Onion Growers Association. Excessive rain or cold, wet conditions after application may reduce plant stand and cause stunting and yield loss. Onion tolerance to Dual Magnum increases with increasing onion size.

Caution A restricted-use herbicide in Washington. 1. Do not apply within 60 days of harvest. 2. Do not harvest green onions. 3. Do not apply this product through any type of irrigation system. 4. Do not graze animals on green forage or stubble. If a fall preplant application of Dual Magnum was used for nutsedge, only one postemergence application at a maximum rate of 1.33 pints/a is allowed. Do not apply more than 2.68 pints/a to dry bulb onions as a combined total across all application timings and use patterns to produce that crop.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide