Asparagus
Bob Parker
Revised October 24, 2008

ASPARAGUS—Seedbeds and Early Establishment
•  paraquat (Gramoxone Max or Gramoxone Inteon)
Rate  0.64 to 1 lb ai/A (1.7 to 2.3 pints/A Gramoxone Max) or 0.5 to 1 lb ai/A (2 to 4 pints/A Gramoxone Inteon)
Time  Apply just before crop emerges, and minimize subsequent soil disturbance. Add nonionic surfactant or crop oil concentrate as directed on the label to the spray mix.
Remarks  Asparagus seeds are hard and require at least 2 to 3 wk to germinate. Established weeds can be controlled with paraquat similar to a stale seedbed treatment. Asparagus emerged at time of treatment will be severely injured or killed.
Caution  A restricted-use pesticide. Do not ingest or inhale spray mist. Wear protective face shields, respirators, and clothing. Acts as contact; absorbs energy produced by photosynthesis, forming peroxides that disrupt living cells.
Site of action  Group 22: photosystem I electron diversion
Chemical family  Bipyridilium
•  linuron (Lorox)
Washington and Oregon only
Rate  1 to 2 lb ai/A
Time  Preemergence. Apply after planting seed 1 to 1.5 inches deep and spraying a 1-inch band of activated charcoal on soil surface directly over row during planting to adsorb and inactivate herbicide.
Remarks  Sprinkler irrigation or rain (0.5 to 1 inch) is required for herbicide activation.
Caution  Do not use on sands, loamy sands, or soils with less than 1% organic matter. See special local needs label for replanting instructions if initial planting fails. Inhibits photosynthesis.
Site of action  Group 7: photosystem II inhibitor
Chemical family  Substituted urea
•  linuron (Lorox)
Washington and Oregon only
Rate  0.5 to 1 lb ai/A
Time  Postemergence on direct-seeded or newly planted crowns. Apply once or twice when ferns are 6 to 18 inches tall and weeds are less than 4 inches tall.
Caution  Do not use a surfactant. Do not exceed 2 lb ai/A per year. (See remarks above.)
Site of action  Group 7: photosystem II inhibitor
Chemical family  Substituted urea
•  terbacil (Sinbar)
Rate  0.8 to 1.6 lb ai/A
Time Apply after planting seed 1 to 1.5 inches deep and spraying a 1-inch band of activated charcoal on soil surface directly over the row during planting to adsorb and inactivate the herbicide.
Remarks  Sprinkler irrigation (0.5 to 2 inches) or rain is required to activate herbicide.
Caution  Do not use on soils containing less than 1% organic matter or on gravelly soils. See label for replanting instructions if initial planting fails. Inhibits photosynthesis.
Site of action  Group 5: photosystem II inhibitor
Chemical family  Uracil
•  fluazifop (Fusilade DX)
Rate  0.0625 to 0.25 lb ai/A (4 to 16 oz/A product)
Time  Apply to actively growing grasses as a directed spray with 1% crop oil or 0.25% nonionic surfactant. Results often are erratic on grasses stressed from lack of vigor, drought, high temperature, low fertility, grass stage of growth, or environmental factors. More mature grasses and quackgrass can be controlled but may require two applications. Annual bluegrass and all fine fescues resist treatment.
Remarks  Identify grasses and adjust rates for susceptibility and stage of weed growth according to label instructions.
Caution  Preharvest interval is 1 day. Do not exceed 24 oz/A product per application or 48 oz/A product per season. Grazing is prohibited. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitors
Chemical family  Aryloxyphenoxy propionate
•  sethoxydim (Poast)
Rate  0.19 to 0.47 lb ai/A (1 to 2.5 pints/A product)
Time  Apply at optimum growth stage as on label. Add 2 pints/A nonphytotoxic crop oil concentrate to improve leaf absorption. Control often is erratic on grasses stressed by drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues; quackgrass can be suppressed.
Remarks  Identify susceptible grasses.
Caution  Do not harvest within 1 day of treatment. Do not exceed two applications or 5 pints/A per season. Allow at least 14 days between sequential applications. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitors
Chemical family  Cyclohexanedione
•  clethodim (Select Max or Intensity One) 
Rate  0.07 to 0.12 lb ai/A (9 to 16 fl oz/A product)
Time  Apply to actively growing grasses at the time specified on the label. Add nonionic surfactant, at 0.25% v/v, to spray mix.
Remarks  Adjust rate for target vegetation. Use the higher rates for perennial grasses.
Caution Do not harvest within 1 day of treatment. 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. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitors
Chemical family  Cyclohexanedione
ASPARAGUS—Established Plantings, Bearing Crop
•  diuron (several brands)
Rate  0.8 to 3.2 lb ai/A
Time  Apply either once within 4 wk 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 yr 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
•  linuron (Lorox)
Oregon and Washington only; dormant season
Rate  1 to 2 lb ai/A
Time  Apply any time during dormancy season before spring harvest begins.
Remarks  Sprinkler irrigation or rain (0.5 to 1 inch) is required to activate herbicide. Preharvest interval is 1 day.
Caution  Do not enter treated areas for 24 hr after applying unless wearing protective clothing. Do not use on sand, loamy sands, or soils with less than 1% organic matter. Inhibits photosynthesis.
Site of action  Group 7: photosystem II inhibitor
Chemical family  Substituted urea
•  linuron (Lorox)
Oregon and Washington only; during harvest
Rate  1 to 2 lb ai/A
Time  Apply before cutting season or immediately after a cutting. Do not exceed 4 lb ai/A or four applications per season.
Caution Preharvest interval is 1 day. Do not enter treated areas for 24 hr after application unless wearing protective clothing. (Note comments above.)
Site of action  Group 7: photosystem II inhibitor
Chemical family  Substituted urea
•  metribuzin (Sencor or TriCor)
Rate  1 to 2 lb ai/A
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  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.
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 mo. Inhibits photosynthesis.
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazinone
•  napropamide (Devrinol)
Rate  4 lb ai/A
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 wk 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
•  halosulfuron (Sandea)
Rate  0.375 to 1.125 oz 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 will enhance control. Do not exceed two applications per season. Spray on 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-mo period. Do not exceed 1.5  oz 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
•  trifluralin (Treflan or Trifluralin)
Rate  0.5 to 2 lb ai/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
•  norflurazon (Solicam DF)
Rate  1.97 to 3.9 lb ai/A (2.5 to 5 lb/A product)
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. Weak on lambsquarters and pigweed. Norflurazon persistence or carryover has shown up in crops that follow norflurazon-treated asparagus. Inhibits yellow pigment formation, bleaching green chlorophyll.
Site of action  Group 12: bleaching; inhibitor of carotenoid biosynthesis
Chemical family  Pyridazinone
•  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  Special local needs label WA-080007, For use only by growers who agree by signature to waiver 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.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  flumioxazin (Chateau)
Rate  3 oz/ai/A (6 oz/A product)
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: protoporphyrinogen oxidase inhibitor
Chemical family  N-phenylphthalimide
•  mesotrione (Callisto) 
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. If weeds in spring 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 increase risk of crop injury.
Site of action  Group 28: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)
Chemical family  Triketone
•  paraquat (Gramoxone Max or Gramoxone Inteon)
Rate  Gramoxone Max—use 0.64 to 1 lb ai/A (1.7 to 2.7 pints/A); Gramoxone Inteon—use 0.62  to 1 lb ai/A (2.5 to 4 pints/A)
Time  Apply before asparagus emerges and/or after last harvest to fields established at least 2 yr.
Remarks  Add nonionic surfactant or crop oil concentrate to the spray as directed on the Gramoxone label. Asparagus emerged at the time of application will be severely injured.
Caution  A restricted-use pesticide. Do not ingest or inhale spray mist. Wear protective face shields, respirators, and protective clothing. Preharvest interval is 6 days. Acts as contact; absorbs energy from photosynthesis, forming peroxides that disrupt living cells.
Site of action  Group 22: photosystem I electron diversion
Chemical family  Bipyridilium
•  glyphosate (several products)
Rate  Consult labels.
Time  Apply at least 1 wk 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
•  fluazifop (Fusilade DX)
Rate  0.44 to 0.9 lb ai/A (6 to 12 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.
Caution  Preharvest interval is 1 day. Do not exceed 48 oz/A per season to bearing asparagus. Grazing is prohibited. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Aryloxyphenoxy propionate
•  sethoxydim (Poast)
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 product per season. Allow at least 14 days between sequential applications. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  clethodim (Select Max or Intensity One) 
Rate  0.07 to 0.12 lb ai/A (9 to 16 fl oz/A product)
Time  Apply to actively growing grasses at the time specified on the container label. Add nonionic surfactant, at 0.25% v/v, to spray mix.
Remarks  Adjust rate for target vegetation. 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. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  2,4-D (Formula 40, AgriSolutions 2,4-D Amine 4, or Savage)
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 hr 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 wk between applications when retreatment 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 fern. Mimics natural plant hormones.
Site of action  Group 4: synthetic auxin
Chemical family  Phenoxy acetic acid
•  clopyralid (Clopyr Ag or Spur)
Rate  0.1875 to 0.25 lb ae/A (0.5 to 0.66 pint/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.
Caution  Preharvest interval is 48 hr. Allow at least 2 wk before cultivating. When applied during the cutting season, some spears may crook (twist). Do not apply during cutting season if crooking cannot be tolerated. Clearcutting spears just before applying may reduce crooking.
Site of action  Group 4: synthetic auxin
Chemical family  Pyridine
•  dicamba (Banvel or Clarity)
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.
Caution  However, do not exceed 1 lb ae/A (16 oz/A product) per growing season. Sprayed spears may be slightly crooked. Discard malformed spears. Mimics natural plant hormones.
Site of action  Group 4: Synthetic auxin
Chemical family  Benzoic acid
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