Established Plantings, Bearing Crop

2,4-D (several trade names)

Rate 1.4 to 1.9 lb ae/a

Time Apply on actively growing weeds, usually in April or May, using a ground sprayer with drop nozzles to reduce contact of spray with crop.

Remarks Workers are not allowed into treated areas until 48 hours after application. Consult your processor or buyer before using these products during the cutting season. If allowed, treat immediately after a cutting. Cut and discard malformed spears appearing after application to avoid off-flavors. Allow at least 6 weeks between applications when re-treatment is required.

Caution Do not apply more than twice per year. Postharvest treatments are suggested to suppress field bindweed and Canada thistle. Use drop nozzles for postharvest treatments to avoid spraying ferns. Mimics natural plant hormones.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid

clethodim (several trade names)

Rate 0.07 to 0.12 lb ai/a

Time Apply to actively growing grasses at the time specified on the container label. Add nonionic surfactant to spray mix, at 0.25% v/v.

Remarks Adjust rate for target weeds. Use the higher rates when controlling perennial grasses.

Caution Preharvest interval is 1 day. Do not exceed 16 fl oz/a of product per application or 64 fl oz/a (0.5 lb ai/a) per season. Allow at least 14 days between treatments.

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

Chemical family Cyclohexanedione

clomazone (Command 3ME)

Rate 1 lb ai/a (2.6 pints/a product

Time Apply to soil surface before weeds and asparagus spears emerge to control of susceptible annual grass and broadleaf weeds. If spears have emerged, make an application after a clean harvest. Cover any exposed plants with soil prior to application. Apply at least 14 days prior to asparagus harvest.

Remarks Apply in a minimum of 10 gal of water per acre. Do not exceed 2.6 pints/a of product per year. Make only one application per year.

Caution Do not allow particle or vapor drift. Off target movement of spray drift or vapors of clomazone can whiten or yellow some plants. Avoid spraying within 1,200 feet of sensitive desirable plants. Note crop restriction intervals on label.

Site of action Group 13: inhibits DOXP synthase

Chemical family Isoxazolidinone

clopyralid (Agristar Spur, Bite, Clean Slate)

Rate 0.1875 to 0.25 lb ae/a (0.5 to 0.66 pints/a product)

Time Apply before or during asparagus cutting season or after harvest, but before fern growth for postemergence control of some broadleaf weeds. Malformed ferns may result from application when spears are longer than 3 inches, or have open seedheads. Make postharvest (layby) applications as soon as possible after harvest, provided weeds are in the proper growth stage.

Remarks Controls only selected broadleaf weeds; check label. A second application may be made, but do not exceed 0.25 lb ae/a (0.66 pint/a) during the growing season. Consult the label for crop rotation restrictions. Not all clopyralid products are labeled for use in asparagus, so make sure you have a label allowing use on asparagus.

Caution Preharvest interval is 48 hours. Allow at least 2 weeks before cultivating. When applied during the cutting season, some spears may crook (twist). Do not apply during cutting season if crooking cannot be tolerated. Clear-cutting spears just before applying may reduce crooking. Spot-spraying perennial weed patches without accurate calibration can result in overapplication and injury to asparagus.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

dicamba (several trade names)

Rate 0.25 to 0.5 lb ae/a

Time Apply immediately after a harvest and at least 24 hr before next cutting, when broadleaf weeds are growing actively during harvest season.

Remarks Multiple applications may be made, but do not exceed 1 lb ae/a (16 oz/a product) per growing season.

Caution Sprayed spears may be slightly crooked. Discard malformed spears. Mimics natural plant hormones.

Site of action Group 4: Synthetic auxin

Chemical family Benzoic acid

diuron (several trade names)

Rate 0.8 to 3.2 lb ai/a

Time Apply either once, within 4 weeks before spears emerge and no later than the early cutting period, or in split applications with the second immediately following final harvest.

Remarks If irrigated in Washington, apply 3.2 lb ai/a in a single treatment. Use higher rates on soils high in clay or organic matter content. Incorporate in top 1 to 2 inches of soil either mechanically or with sprinkler irrigation.

Caution Do not exceed 2.4 lb ai/a per application in split treatments. See label restrictions on planting sensitive crops within 2 years of last application. Rotate with simazine or other herbicides to reduce weed shifts and minimize soil residues. Inhibits photosynthesis.

Site of action Group 7: photosystem II inhibitor

Chemical family Substituted urea

fluazifop (Fusilade DX)

Rate 0.09 to 0.375 lb ai/a (6 to 24 oz/a product)

Time Direct spray to actively growing grasses with 1% crop oil or 0.25% nonionic surfactant.

Remarks Identify grasses and adjust rates depending on susceptibility and stage of weed growth according to label. Results often are erratic if grasses are stressed from lack of vigor, drought, high temperature, or low fertility. More mature grasses and quackgrass can be controlled but may require two applications. Annual bluegrass and all fine fescues resist treatment. Space sequential applications a minimum of 14 days apart.

Caution Preharvest interval is 1 day. Do not apply more than 48 oz/a per season to bearing asparagus.

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

Chemical family Aryloxyphenoxy propionate

flumioxazin (Chateau SW and several others)

Rate 3 oz ai/a (6 oz/a of 51% active ingredient products)

Time Apply to dormant asparagus at least 14 days prior to spear emergence.

Remarks Use for preemergence weed control and to aid postemergence burndown of many annual and perennial weeds where established asparagus is dormant. For enhanced control of emerged weeds, tank mix with paraquat. Tank-mixes applied to assist in controlling emerged weeds must be applied with a nonionic surfactant. A spray-grade nitrogen source may be added to increase herbicidal activity. Flumioxazin controls susceptible broadleaf weeds better than grasses.

Caution Do not exceed 3 oz ai/a (6 oz/a product) per growing season. Do not apply within 14 days of spear emergence. Application to nondormant asparagus may result in unacceptable crop injury.

Site of action Group 14: inhibits protoporphyrinogen oxidase (PPO)

Chemical family N-phenylphthalimide

glyphosate (several trade names)

Rate Consult labels.

Time Apply at least 1 week before spears emerge, or after final harvest and removal of all spears, or wait until ferns develop and apply as a directed or shielded application.

Remarks Spot treatment in season: apply immediately after clean cutting, before new spears emerge.

Caution Do not treat more than 10% of total field area to be harvested. Preharvest interval is 5 days. Consult label for specific rates, times of application, and perennial species controlled. Do not contact ferns, stems, or spears because crop may be seriously injured. Do not exceed 8 lb ai/a per year. Inhibits three amino acids and protein synthesis.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted

halosulfuron (Sandea, Stadia)

Rate 0.023 to 0.073 lb ai/a (0.5 to 1.5 oz/a product)

Time Apply before, during, or after harvest.

Remarks Controls several broadleaf weeds and yellow nutsedge. A nonionic surfactant is not recommended for applications made before or during the harvest season. Spray contacting asparagus ferns may cause temporary yellowing; minimize crop injury by using drop nozzles to direct spray below the ferns. Use a nonionic surfactant or crop oil concentrate with postharvest applications.

Caution Do not apply more than twice per crop cycle or 12-month period. Do not exceed 0.094 ai /a (2 oz/a product) per season. Consult the label for crop rotation restrictions.

Site of action Group 2: acetolactate synthase (ALS) inhibitor

Chemical family Sulfonylurea

linuron (Lorox DF)

Rate 1 to 2 lb ai/a (2 to 4 lb/a product)

Time Apply any time during dormancy season before spring harvest begins. Apply immediately after a cutting. In fern stage, make a single application of 2 lb ai/a (4 lb/a product) as directed spray to base of plants. Do not exceed 4 lb/a, or four applications per season.

Remarks Sprinkler irrigation or rain (0.5 to 1 inch) is required to activate herbicide.

Caution Preharvest interval is 1 day. Do not enter treated areas for 24 hours after applying unless wearing protective clothing. Do not use on sand, loamy sands, or soils with less than 1% organic matter. See label for crop rotation restrictions West of the Rockies.

Site of action Group 7: photosystem II inhibitor

Chemical family Substituted urea

mesotrione (several trade names)

Rate 0.09375 to 0.24 lb ai/a (3 to 7.7 fl oz/a product)

Time Apply in spring before spears emerge, or after final harvest, or both.

Remarks Use low rate to control emerged weeds. Use higher rate range for preemergence control. For best preemergence control in spring, apply after mowing, disking, or other tillage but before spears emerge. In spring, if weeds are emerged, adding crop oil concentrate or nonionic surfactant plus a spray-grade UAN or AMS fertilizer will enhance weed control.

Caution Do not exceed 0.24 lb ai/a (7.7 fl oz/a product) or two applications per year. In postharvest applications, using an adjuvant increases the risk of crop injury.

Site of action Group 28: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)

Chemical family Triketone

metribuzin (several trade names)

Rate 1 to 2 lb ai/a (1.33 to 2.66 lb/a 75DF, 1 to 2 pints/a 4F)

Time Apply once per season or split treatment with 0.5 to 1 lb ai/a in spring + 0.5 to 1.5 lb ai/a after final harvest but before ferns emerge. Make spring treatment at least 14 days before first harvest.

Remarks Apply in spring prior to spear emergence. Do not apply over the top of emerged spears or injury will result. Do not harvest less than 14 days after application. Can apply with ground sprayers or a center pivot but must sprinkler-irrigate to activate if rain is lacking. Use lower rate on soils with low organic matter content. Do not exceed 0.5 inch irrigation water after application. May also apply after the last harvest of the season but prior to any emergence..

Caution Do not exceed 2 lb ai/a per year. Injury has been reported in Washington when used on coarse soils with sprinkler irrigation. See label for restrictions on planting sensitive crops within 18 months. Inhibits photosynthesis.

Site of action Group 5: photosystem II inhibitor

Chemical family Triazinone

napropamide (Devrinol 50DF, Devrinol DF-XT, Devrinol 2-XT)

Rate 4 lb ai/a (8 lb/a 50DF)

Time Apply either before harvest in early spring or during winter dormancy to weed-free soil.

Remarks Requires sprinkler irrigation or rain to wet soil 2 to 4 inches deep immediately after application from March through October or within 2 weeks from November through February. Research in the Pacific Northwest shows immediate, shallow mechanical incorporation enhances weed control.

Caution Inhibits root growth.

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

Chemical family Acetamide

norflurazon (Solicam DF)

Rate 1.97 to 3.93 lb ai/a (2.5 to 5 lb/a Solicam DF)

Time Apply once per season to established crowns in late fall or early spring, preferably before weeds begin to germinate.

Remarks Adjust rates, depending on soil texture and organic matter.

Caution Do not apply to fields with shallow crowns. Preharvest interval is 14 days. Control is weak on lambsquarters and pigweed. Norflurazon persistence or carryover has shown up in crops that follow norflurazon-treated asparagus. Consult the label for crop rotation restrictions. Inhibits yellow pigment formation, bleaching green chlorophyll.

Site of action Group 12: bleaching; inhibitor of carotenoid biosynthesis

Chemical family Pyridazinone

paraquat (several trade names)

Rate 0.62 to 1 lb ai/a

Time Apply before asparagus emerges and/or after last harvest to fields established at least 2 years.

Remarks Add nonionic surfactant or crop oil concentrate to the spray as directed on the product label. Asparagus emerged at the time of application will be severely injured.

Caution A restricted-use herbicide. Do not ingest or inhale spray mist. Wear protective face shields, respirators, and protective clothing. Preharvest interval is 6 days. Acts as contact herbicide; absorbs energy from photosynthesis, forming peroxides that disrupt living cells.

Site of action Group 22: photosystem I electron diversion

Chemical family Bipyridilium

pelargonic acid (Scythe)

Rate Apply in a total water volume of 75 to 200 gal/a. Apply as a 3% to 5% (v/v) solution on young, small, annual weeds and 5% to 7% (v/v) solution on perennial herbaceous weeds or annual weeds over 6 inches tall. For difficult to control weeds and maximum vegetation control use 7% to 10% (v/v).

Time Apply before asparagus emerges to control winter annual or early emerged weeds. Apply during or after asparagus harvest season, but don't allow spray to contact emerged asparagus spears or fern. Small weeds are easier to control than larger weeds. Warm weather promotes rapid activity on plants.

Remarks Apply as a spot treatment or as a directed and shielded spray avoiding contact with all desirable vegetation. Contact of spray or spray drift with emerged asparagus will damage spears or fern. Repeat applications required to control new weeds emerging from seed or underground vegetative parts. Broadleaf weeds are generally controlled better than grass weeds and repeated use may select for grasses.

Caution Pelargonic acid is a nonselective herbicide; any spray contacting desirable vegetation will likely result in damage.

Site of action Group 26: unknown. Disrupts cell membranes, causing leakage from the cells and rapid wilting.

Chemical family Carboxylic acid

pendimethalin (Drexel Aquapen, Prowl H2O, Satellite Hydrocap)

Rate 1.14 to 3.9 lb ai/a (2.4 to 8.2 pints/a). On sandy soils: 2.4 pints/a maximum.

Time Apply preemergence at least 14 days prior to first harvest of spears, or after seasonal harvest of spears is completed. Remove any early emerged spears prior to application.

Caution Do not apply more than 2.4 pints/a on sandy soils. Do not apply more than 8.2 pints/a per season. Do not apply postemergence over the top of emerged spears. Not labeled for chemigation application.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

pendimethalin + metribuzin (Tripsin ZC)

Rate 2.6 to 3.9 lb ai/a pendimethalin and 1 to 1.5 lb ai/a metribuzin (116 to 172 fl oz/a). On sandy soils: 50 fl oz/a maximum.

Time Apply preemergence at least 14 days prior to first harvest of spears or after the last harvest of season. Do not apply over the top of emerged spears or severe injury will result. Remove any emerged spears prior to application.

Caution Do not apply more than 172 fl oz/a per season. Not labeled for chemigation or aerial application.

Site of action Group 3 and 5: microtubule assembly inhibitor and photosystem II inhibitor

Chemical family (pendimethalin) Dinitroaniline and metribuzin (Triazinone)

quinclorac (QuinStar 4L)

Rate 0.375 lb ai/a (12.6 fl oz/a product)

Time Apply after the last harvest of the season and prior to the first frost as a broadcast application. Time application so that field bindweed or other target weeds have emerged and before the asparagus fern has grown substantially and filled in. Adequate spray coverage on the target weeds may be difficult with later applications once the asparagus canopy is full and later applications have not been tested in the PNW.

Remarks Only one application up to 12.6 fl oz/a is allowed per calendar year. Apply in a minimum of 10 gal of water per acre. Crop oil concentrate may be included in the spray mixture In improve activity. Controls or suppresses field bindweed (morningglory), Canada thistle, perennial sowthistle, common lambsquarters, and Russian thistle. Also controls barnyardgrass, green foxtail, and large crabgrass.

Caution Do not allow spray drift or apply when wind speed Is greater than 10 mph. Do not apply by air. Note crop rotation restriction intervals on the label, which for some crops is 24 months. Only wheat or grain sorghum can be replanted for 10 months following application.

Site of action Group 4: synthetic auxin

Chemical family Quinoline carboxylic acid

S-metolachlor (Dual Magnum)

Washington only

Rate 1.25 to 1.9 lb ai/a (1.33 to 2 pints/a Dual Magnum)

Time Apply to dormant established asparagus in spring at least 16 days before spears emerge, or after harvest season.

Remarks SLN label WA-080007. For use only by growers who agree, by signature, to waive Syngenta Crop Protection from all liability and indemnification. Adjust rate to soil type. Apply in at least 20 gal/a of water. Will not control emerged weeds.

Caution Preharvest interval is 16 days. Do not exceed 1.9 lb ai/a (2 pints/a product) or one application per year. Not labeled for chemigation application.

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

Chemical family Chloroacetamide

sethoxydim (several trade names)

Rate 0.19 to 0.47 lb ai/a (1 to 2.5 pints/a product)

Time Apply at optimum growth stage listed on the 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. Resistant grasses include annual bluegrass and all fine fescues; quackgrass can be suppressed.

Caution Preharvest interval is 1 day. Do not exceed two applications, or 5 pints/a of product per season. Allow at least 14 days between sequential applications.

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

Chemical family Cyclohexanedione

sulfentrazone (Shutdown, Willowood Sulfentrazone 4SC)

Rate 0.14 to 0.375 lb ai/a (4.5 to 12 fl oz/a product)

Time Apply in spring prior to spear and weed emergence.

Remarks Apply only to crowns that have been established at least 12 months and are healthy and vigorous. Adjust rates based on soil texture, soil organic matter content, and pH according to label guidelines. Apply in 10 to 40 gal of spray solution per acre. Apply only one application in a 12 month period.

Caution Preharvest interval is 14 days. Do not use on soils classified as sands and with less than 1% organic matter content. Use lowest rate labeled for your soil type to avoid crop injury. See plant back and crop rotation restrictions on label.

Site of action Group 14: inhibits protoporphyrinogen oxidase (PPO)

Chemical family Triazinone

terbacil (Sinbar, Sinbar WDG)

Rate 1.2 to 2.5 lb ai/a (1.5 to 2.5 lb/a product)

Time Apply prior to spear emergence, or immediately after clean cutting all spears.

Remarks Sprinkler irrigation (0.5 to 2 inches) or rain is required to activate herbicide. Use the lower rate on coarse textured soils, and the higher rate on fine soils.

Caution Preharvest interval is 5 days. See rate restrictions on label for coarse textured soils with low organic matter in Columbia Basin. Crop injury may result if used on diseased or low vigor asparagus. Use lowest rate labeled for your soil type to avoid crop injury. Terbacil is persistent in soil; plant back to most crops requires 2 or more years. See label for crop rotation restrictions.

Site of action Group 5: photosystem II inhibitor

Chemical family Uracil

trifluralin (several trade names)

Rate 0.5 to 2 lb ai/a (1 to 4 pints/a)

Time Apply either total amount before first harvest or after final harvest, or split treatments and apply half before first harvest and half after final harvest.

Remarks Chop and thoroughly mix crop and weed residue into soil before application. Mechanically incorporate the herbicide within 24 hours after application to reduce volatilization.

Caution Consult label for application rates, depending on soil type and organic matter content. Inhibits mitosis in both shoots and roots.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline