Forage Alfalfa
Bob Parker
Revised November 1, 2008
FORAGE ALFALFA—Annual Grass and Broadleaf Weeds in Establishing New Seedings
•  benefin (Balan DF)
Rate  1.2 to 1.5 lb ai/A
Time  Apply to a clean, clod-free soil surface before planting, and incorporate 2 to 3 inches deep within 4 hr after application.
Remarks  Use lower rates on coarse and medium soils, higher rates on fine soils. Avoid overlapping spray.
Caution  Do not plant wheat, barley, rye, other domestic grasses, and onions for 10 mo after application. Do not plant milo (grain sorghum), corn, oats, sugar beets, other root crops, or spinach for 12 mo after application.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  EPTC (Eptam)
Rate  2 to 4 lb ai/A
Time  Apply before planting and incorporate immediately and thoroughly into soil.
Remarks  Use lower rate on sandy soils, higher rate on silty and clay soils and for quackgrass and nutsedge control. Incorporate 2 to 3 inches deep with power-driven rotary tiller for band or broadcast application, or set a tandem disk 4 to 6 inches deep and use it twice at right angles for broadcast application.
Caution  Crop may be temporarily injured. Do not use EPTC if a grass or grain companion crop is to be planted with the alfalfa.
Site of action  Group 8: lipid synthesis inhibitor but not an ACCase inhibitor
Chemical family  Thiocarbamate
•  trifluralin (Treflan HFP)
Rate  0.5 to 0.75 lb ai/A
Time  Before planting, apply and thoroughly incorporate into top 2 to 3 inches of soil.
Remarks  Use lower rates on coarse and medium soils, higher rates on fine soils.
Caution  Some crop stand reduction and stunting may occur with this use. Do not plant sugar beets, red beets, spinach, proso millet, corn, sorghum, oats, or annual or perennial grass crops or grass mixtures for 12 mo after a spring application or 14 mo after a fall application. Moldboard plowing to a depth of 12 inches before planting these crops reduces the possibility of crop injury. If land has not been irrigated, do not plant these crops for 18 mo after a spring application or 20 mo after a fall application.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  pendimethalin (Prowl H2O) 
Rate  0.475 to 0.95 lb ai/A (1 to 2 pints/A product)
Time  Apply before weeds emerge,  when alfalfa has a fully expanded second trifoliolate leaf, and before alfalfa is 6 inches tall.
Remarks  Controls most annual grasses and several broadleaf weeds, including dodder, as they germinate. Soil incorporation with rain or sprinkler irrigation enhances control. Will not control emerged weeds.
Caution  Do not harvest for hay or forage within 50 days of application. Do not exceed 4 quarts/A of product per year. Refer to label for crop rotation restrictions.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  imazethapyr (Pursuit)
Rate  0.047 to 0.094 lb ai/A (1.08 to 2.16 oz/A Pursuit DG or 3 to 6 oz/A Pursuit W)
Time  Apply after seedling alfalfa has reached second trifoliate growth stage and when most weeds are actively growing and 1 to 3 inches tall or across.
Remarks  Adding an adjuvant (nonionic surfactant or crop oil concentrate) and a liquid fertilizer solution is required. Temporary height reduction or slight leaf yellowing may occur soon after application. Weeds under stress are less susceptible to control. Apply at least 1 hr before rain or overhead irrigation.
Caution  Do not feed, graze, or harvest alfalfa for 30 days after application. See recropping restrictions before using. Some rotation crops cannot be planted within 40 mo of application. Use only rotation crops harvested at maturity for feed or food.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Imidazolinone
•  imazamox (Raptor)
Rate  0.031 to 0.047 lb ai/A (4 to 6 oz/A product)
Time  Apply postemergence to actively growing weeds when most are 1 to 3 inches tall or across and seedling alfalfa is in the second trifoliate leaf stage or later.
Remarks  Adding an adjuvant (nonionic surfactant or crop oil concentrate) and a liquid fertilizer or ammonium sulfate solution is required. Alfalfa height may be temporarily reduced after treatment. Weeds under stress are less susceptible to control. Apply at least 1 hr before rain or overhead irrigation.
Caution  Do not exceed 6 oz/A product per season. Note recropping restrictions before use. Some crops cannot be planted within 26 mo of application. Only rotational crops harvested at maturity may be used for feed or food.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Imidazolinone
FORAGE ALFALFA—Annual Broadleaf Weeds in Establishing New Stands
•  2,4-DB (Butyrac or Butoxone)
Rate  0.5 to 1.5 lb ae/A
Time  Apply postemergence to seedling weeds less than 3 inches tall. See label for size of alfalfa when treating.
Remarks  Controls broadleaf weeds only. Use the higher rate in arid areas. 2,4-DB is progressively more damaging to alfalfa as it matures. Certain annual broadleaf weeds such as smartweed, prostrate knotweed, redroot pigweed, and chickweed have proven resistant, especially under conditions west of the Cascades. Will not control grasses.
Caution  Do not graze seedling alfalfa within 60 days after application.
Site of action  Group 4: synthetic auxin
Chemical family Phenoxy acetic acid
•  bromoxynil  (Buctril)
Rate  0.25 to 0.375 lb ai/A or 0.5 lb ai/A when applied through sprinkler irrigation
Time  Apply in spring or fall when alfalfa has at least four trifoliate leaves and weeds listed as susceptible or moderately susceptible have no more than four leaves or are no more than 2 inches tall or 1 inch wide.
Remarks  For broadleaf weeds only. Crop may be temporarily stunted, but yield should not drop.
Caution  Do not treat if temperature exceeds or is expected to exceed 70°F during the 3 days after application by ground, or exceeds 85°F if applied through the sprinkler; crop injury may be unacceptable. Do not add a surfactant or crop oil because crop injury may increase. Do not cut for feed or graze for 30 days after application.
Site of action  Group 6: photosystem II inhibitor
Chemical family  Nitrile
•  bromoxynil (Buctril) +
•  2,4-DB
Rate  0.25 lb ai/A bromoxynil + 0.5 lb ae/A 2,4-DB
Time  Apply in spring or fall when alfalfa has at least four trifoliate leaves.
Remarks  For broadleaf weeds only. For improved control of tansy mustard, henbit, pigweed, and kochia compared to bromoxynil. Do not apply through a sprinkler. Follow the label for 2,4-DB. Crop may be temporarily stunted, but yields should not drop.
Caution  Do not treat if temperature exceeds or is expected to exceed 70°F during the 3 days after application; crop injury may be unacceptable. Do not add a surfactant or crop oil because crop injury may increase. Do not cut for feed or graze for 30 days after application.
Site of action  (bromoxynil) Group 6: photosystem II inhibitor; (2,4-DB) Group 4: synthetic auxin
Chemical family  (bromoxynil) nitrile; (2,4-DB) phenoxy acetic acid
FORAGE ALFALFA—Annual Grass Weeds in Establishing New Stands
•  sethoxydim (Poast or Poast Plus)
Rate  0.19 to 0.47 lb ai/A
Time  Apply to actively growing annual or perennial grasses at the appropriate stage of grass growth as indicated by the label.
Remarks  For grass control only. See label for specific herbicide rates, weed species, and weed size. Always add a nonphytotoxic oil concentrate to the spray tank at 2 pints for each acre of alfalfa treated. Sethoxydim is most effective on actively growing grasses before they have been cut but before they reach the maximum size indicated on the label. Larger, more mature grasses can be controlled, but two applications may be required. Sethoxydim will not control annual bluegrass or any of the fine fescues and is weak on downy brome and quackgrass.
Caution  Control may be erratic if grasses are stressed by drought, temperature extremes, insect damage, herbicide injury, or other factors. Do not apply if rain is expected within 1 hour after application. Do not apply within 7 days of feeding, grazing, or harvesting for green chop or silage, or within 14 days of harvesting hay. Do not exceed 0.94 lb ai/A in one season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  clethodim (Select, Select 2EC, Select Max, Intensity, or Intensity One)
Rate  Select, Select 2EC, or Intensity—use 0.094 to 0.125 lb ai/A (6 to 8 fl oz/A product). Select Max or Intensity One—use 0.07 to 0.24 lb ai/A (9 to 32 fl oz/A product).
Time  Apply to actively growing annual or perennial grasses at the stage of grass growth indicated on label.
Remarks  For grass control only. See label for specific weed species and weed size. Always add a crop oil concentrate containing at least 15% emulsifier at 1% v/v in the finished spray volume. Adding ammonium sulfate has improved control of difficult-to-control grasses. Clethodim is most effective on actively growing grasses before they reach the maximum size indicated on label. In irrigated alfalfa, for best results, apply within 2 to 4 days after  irrigation. Use at least 0.125 lb ae/A (8 oz/A of Select) or 0.129 lb ai/A (17 oz/A of Select Max) to control annual bluegrass.
Caution  Control may be erratic if grasses are stressed by drought, temperature extremes, insect damage, herbicide injury, or other factors, or if grasses are larger than indicated on label. Do not apply if rain is expected within 1 hr after application. Do not apply within 15 days of grazing, feeding, or harvesting for forage or hay. Do not exceed 0.5 lb ai/A per season (32 fl oz/A of Select or 64 fl oz/A of Select Max).
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
FORAGE ALFALFA—Summer Annual Grasses in Established Stands
•  trifluralin (Treflan TR-10 or Treflan HFP)
Rate  2 lb ai/A
Time  Apply before weeds emerge.
Remarks  Trifluralin must be activated by a single rain or overhead sprinkler irrigation of at least 0.5 inch or by furrow irrigation that thoroughly wets the beds between furrows. If not activated within 3 days, mechanically incorporate trifluralin with equipment that will not damage the alfalfa. May be applied during dormancy or during the growing season after a cutting. Apply before weeds are expected to germinate; trifluralin will not control established weeds.
Caution  Do not cut for hay or graze within 21 days of application. Apply no more than 2 lb ai/A per growing season. If rotating out of established alfalfa the year after applying, plant only crops for which trifluralin can be applied as a preplant treatment, or injury may result.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  sethoxydim (Poast or Poast Plus)
Rate  0.19 to 0.47 lb ai/A
Time  Apply to actively growing annual or perennial grasses at stage of grass growth indicated on label.
Remarks  See label for specific herbicide rates, weed species, and weed size. Always add a nonphytotoxic oil concentrate to the spray tank at 2 pints/A. Sethoxydim is most effective on actively growing grasses before they are cut or reach the maximum size indicated on label. Larger, more mature grasses can be controlled, but two applications may be required. Sethoxydim will not control annual bluegrass or any of the fine fescues.
Caution  Control often is erratic on grasses stressed by drought, temperature extremes, insect damage, herbicide injury, or other factors. Do not apply if rain is expected within 1 hr after application. Do not apply within 7 days of feeding, grazing, or harvesting for green chop or silage, or within 14 days of harvesting hay. Do not exceed 0.94 lb ai/A in one season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  clethodim (Select, Select 2EC, Select Max, Intensity, or Intensity One)
Rate  Select, Select 2EC, or Intensity—use 0.094 to 0.125 lb ai/A (6 to 8 fl oz/A product). Select Max or Intensity One—use 0.07 to 0.24 lb ai/A (9 to 32 fl oz/A product).
Time  Apply to actively growing annual or perennial grasses at stage of grass growth indicated on label.
Remarks  For grass control only. Refer to label for specific weed species and weed size. Always add a crop oil concentrate containing at least 15% emulsifier at 1% v/v in the finished spray volume. Adding ammonium sulfate has improved control of difficult-to-control grasses. Clethodim is most effective on actively growing grasses before they reach the maximum size indicated on label. In irrigated alfalfa, for best results, apply within 2 to 4 days after an irrigation. Use the higher rate under heavy grass pressure and/or when annual bluegrass is more mature.
Caution  Control may be erratic if grasses are stressed by drought, temperature extremes, insect damage, herbicide injury, or other factors, or if grasses are larger than indicated on label. Do not apply if rain is expected within 1 hr after application. Do not apply within 15 days of grazing, feeding, or harvesting for forage or hay. Do not exceed 0.5 lb ai/A per season (32 fl oz/A of Select or 64 fl oz of Select Max).
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
FORAGE ALFALFA—Quackgrass, Volunteer Cereals, and Annual Grasses in New or Established Stands
•  pronamide (Kerb)
Rate  0.25 to 2 lb ai/A
Time  Apply October through early December.
Remarks  The low rates are for grass suppression only. Herbicidal activity is optimal when applied under cool conditions (55°F or cooler) and followed by rain or overhead irrigation. Use higher rates for perennial grass control. On fields to be treated, remove residue by burning or tilling into the soil.
Caution  A restricted-use herbicide. Apply on new plantings only after alfalfa reaches the first trifoliate leaf stage. Do not apply preplant, preemergence, or in the seed-leaf stage. Do not graze treated fields or feed clippings or crop residue to livestock within 25 days of applying (if less than 1.5 lb ai/A) or within 45 days (if 1.5 to 2 lb ai/A).
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Benzamide
•  clethodim (Select, Select 2EC, Select Max, Intensity, or Intensity One)
Rate  Select, Select 2EC, or Intensity—use 0.094 to 0.125 lb ai/A (6 to 8 fl oz/A product). Select Max or Intensity One—use 0.07 to 0.24 lb ai/A (9 to 32 fl oz/A product).
Time  Apply to actively growing annual or perennial grasses at stage of grass growth indicated on label.
Remarks  For grass control only. Weak on quackgrass. See label for specific weed species and weed size. Always add a crop oil concentrate containing at least 15% emulsifier at 1% v/v in the finished spray volume. Adding ammonium sulfate has improved control of difficult-to-control grasses. Clethodim is most effective on actively growing grasses before they reach the maximum size indicated on label. Use the higher rate under heavy grass pressure and/or when annual bluegrass is more mature.
Caution  Control may be erratic if grasses are stressed by drought, temperature extremes, insect damage, herbicide injury, or other factors, or if grasses are larger than indicated on label. Do not apply if rain is expected within 1 hr after application. Do not apply within 15 days of grazing, feeding, or harvesting for forage or hay. Do not exceed 0.5 lb ai/A (32 fl oz/A of Select or 64 fl oz of Select Max) per season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  sethoxydim (Poast or Poast Plus)
Rate  0.19 to 0.47 lb ai/A
Time  Apply to actively growing annual or perennial grasses at stage of grass growth indicated by the label.
Remarks  Refer to label for specific herbicide rates, weed species, and weed size. Always add a nonphytotoxic oil concentrate to the spray tank at 2 pints/A. Sethoxydim is most effective on actively growing grasses before they have been cut and before they reach the maximum size indicated on label. Larger, more mature grasses can be controlled, but two applications may be required. Sethoxydim will not control annual bluegrass or any of the fine fescues.
Caution  Control often is erratic if grasses are stressed by drought, temperature extremes, insect damage, herbicide injury, or other factors. Do not apply if rain is expected within 1 hr after application. Do not apply within 7 days of feeding, grazing, or harvesting for green chop or silage, or within 14 days of harvesting hay. Do not exceed 0.94 lb ai/A in one season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
FORAGE ALFALFA—Winter Annual Grasses and Broadleaf Weeds in Established Stands
•  paraquat (Gramoxone Inteon or Firestorm)
Rate  Firestorm—0.49 to 1 lb ai/A (1.3 to 2.7 pints/A product). Gramoxone Inteon—0.25 to 0.375 lb ai/A (2 to 3 pints/A product). Add nonionic surfactant with 75% or greater surface-active agent at 1 pint, or crop oil concentrate with 15% to 20% approved emulsifier at 1 gal/100 gal spray mix.
Time  Apply after last fall cutting when crop is dormant and before spring growth starts. 
Remarks  Apply soon after weeds germinate. Alfalfa should be dormant. Do not apply if fall regrowth after the last cutting is more than 6 inches high or if spring regrowth is more than 2 inches high. Control decreases as weed size increases. Use 20 gal/A or more water carrier for ground application. Paraquat is a contact herbicide. Excellent knockdown plus residual control usually is obtained by combining paraquat with one of the residual herbicides.
Caution  A restricted-use herbicide. Do not pasture animals in treated fields before first cutting. Do not graze, cut, or harvest within 42 days of application. Do not apply more than once per season. Follow safety precautions on the labels.
Site of action  Group 22: photosystem I electron diversion
Chemical family  Bipyridilium
•  diuron (Karmex or Direx)
Rate  1.2 to 2.4 lb ai/A
Time  Apply at start of dormancy (late October through early December).
Remarks  Apply as a broadcast spray to dormant alfalfa established more than 1 year. Not very effective on downy brome (cheatgrass) or volunteer cereals.
Caution  Do not use on soils with less than 1% organic matter. Do not apply to snow-covered or frozen soil. Do not replant treated area to any crop within 2 yr after application.
Site of action  Group 7: photosystem II inhibitor
Chemical family  Substituted urea
•  metribuzin (Sencor, TriCor)
Rate  0.25 to 1 lb ai/A
Time  Apply in the fall after crop is dormant and before spring growth starts.
Remarks  Consult label for the product used. Broadcast spray dormant alfalfa established 1 yr or more. Use the 0.25-lb rate of Sencor if the only target weed is common chickweed. 
Caution  Do not use on sand or use Sencor on soils with a pH greater than 8.2. Do not apply on snow-covered or frozen ground. Use lower rates on coarse, sandy soils or soils low in organic matter. Do not graze or harvest within 28 days after application. Stunting and chlorosis may occur, particularly in nondormant alfalfa. Stress—which may be caused in part by low fertility, disease, insects, overcutting, drought, or frost—may increase the possibility of crop injury. Avoid overlapping because injury may occur. See herbicide label for recropping recommendations.
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazinone
•  terbacil (Sinbar)
Rate  0.4 to 1.2 lb ai/A
Time  Apply to dormant alfalfa after frost but before January 1.
Remarks  Apply as a broadcast spray to dormant alfalfa established 1 yr or more. Use lower rate on coarse, sandy soils or soils low in organic matter.
Caution  Do not use on sand, loamy sand, or gravelly soil. Do not use on soils with less than 1% organic matter. Do not apply on snow-covered or frozen ground. Do not replant treated areas to any crop within 2 yr after last application.
Site of action  Group 5: photosystem II inhibitor
Chemical family  Uracil
•  hexazinone (Velpar)
do not use on seed crops in Idaho and Oregon
Rate  0.45 to 1.5 lb ai/A
Time  Apply in fall after crop is dormant and before spring growth starts. On nondormant and semidormant varieties, apply in winter when alfalfa is least actively growing.
Remarks  Labels differ slightly between Velpar formulations. Use lower rate on coarse, sandy soils low in organic matter. Apply to alfalfa established at least one growing season but not on snow-covered or frozen ground. Results are best if applied before or soon after weeds emerge (before weeds are 2 inches tall or across).
Caution  Do not use on alfalfa grown for seed except in Walla Walla County, WA. Do not graze or harvest within 30 days after application. Do not apply to alfalfa growing under stress from insect, disease, winter injury, or other factors. Very heavy rain or irrigation soon after application may result in crop injury or nonperformance of the herbicide. Hexazinone persists in soil up to 24 mo. Read label for crop rotation restrictions and other cautions.
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazinone
•  norflurazon (Zorial)
Rate  1 to 2 lb ai/A
Time  Apply no earlier than 5 mo after crop emerges or to dormant alfalfa or after a harvest in the growing crop before weeds emerge.
Remarks  Use lower rates on coarse and medium soils, higher rate on fine soils. At least 0.5 inch of overhead moisture required to move herbicide into soil. Fall or winter applications are recommended in nonirrigated areas with less than 15 inches annual moisture (rain and snow combined) or less than 4 inches of spring rain. Will not control established weeds. Control established weeds or weeds that emerge before activation with a labeled postemergence herbicide.
Caution  Do not apply to seedling alfalfa earlier than 5 mo after planting. Do not exceed 2 lb ai/A per year. Preharvest interval is 28 days. Note rotation restrictions. Bioassay soils containing more than 65% sand before crop rotation. Rotation crops can be planted when no signs of phytotoxicity are observed in bioassay plants for 4 mo after emergence.
Site of action  Group 12: bleaching; inhibits carotenoid biosynthesis
Chemical family  Pyridazinone
•  trifluralin (Treflan HFP or Treflan TR-10)
Rate  2 lb ai/A
Time  Apply before weeds emerge.
Remarks  Trifluralin must be activated by a single rain or overhead sprinkler irrigation of at least 0.5 inch or by furrow irrigation that thoroughly wets beds between furrows. If not activated within 3 days, mechanically incorporate trifluralin with equipment that won’t damage alfalfa. May be applied during dormancy or during the growing season after a cutting. Apply before weed seeds germinate; trifluralin will not control established weeds. If downy brome and other winter annual grasses are targets, apply immediately after a cutting between August 1 and October 1.
Caution  Do not cut for hay or graze within 21 days after application. Apply no more than 2 lb ai/A per growing season. Note recropping restrictions. In the year after application, plant only those crops for which trifluralin is registered as a preplant treatment, or crop may be injured.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  pendimethalin (Prowl H2O)
Rate  1 to 3.8 lb ai/A (1 to 4 quarts/A product)
Time  Apply to dormant, established alfalfa.
Remarks  Controls most annual grasses and certain broadleaf weeds, including dodder, as they germinate. Apply to alfalfa that has gone through one growing season. Soil incorporation with rainfall or sprinkler will enhance activity.
Caution  Do not apply to seedling alfalfa. Do not harvest for hay or forage for at least 50 days after application. Do not exceed 4 quarts/A of product per year. Refer to label for crop rotation restrictions.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  flumioxazin (Chateau)
Rate  2 oz ai/A (4 oz product/A)
Time  Apply preemergence to the weeds.
Remarks  Applications should be made as soon as possible after cutting and removing alfalfa to minimize crop injury. Flumioxazin will burn treated leaves and stems. A second application can be made 60 days after the first application. Will only give fair control of many annual grasses. If weeds are present when applications are made after the last harvest in the fall or when the alfalfa is dormant, apply with paraquat to burndown weeds present.
Caution  Do not harvest or graze within 25 days of application. Do not make second application within 60 days of the first application. Do not exceed 8 oz of Chateau during a single growing season.
Site of action  Group 14, protoporphyrinogen oxidase (PPO) inhibitor
Chemical family  N-phenylphthalimide

FORAGE ALFALFA—Annual Grasses and Broadleaf Weeds in Established Stands
•  imazethapyr (Pursuit)
Rate  0.047 to 0.094 lb ai/A (1.08 to 2.16 oz/A Pursuit DG or 3 to 6 oz/A Pursuit W)
Time  Apply to established alfalfa in the fall, in the spring to dormant or semidormant alfalfa (less than 3 inches of regrowth), or between cuttings and when most weeds are actively growing and 1 to 3 inches tall or across.
Remarks  Adding an adjuvant (nonionic surfactant or crop oil concentrate) and a liquid fertilizer solution is required. Temporary height reduction or slight leaf yellowing may occur soon after application. Weeds under stress are less susceptible to control. Apply at least 1 hr before rain or overhead irrigation.
Caution  Do not feed, graze, or harvest alfalfa for 30 days after applying. Note recropping restrictions before use. Some rotation crops cannot be planted within 40 mo of application. Only rotation crops harvested at maturity may be used for feed or food.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Imidazolinone
•  imazamox (Raptor)
Rate  0.031 to 0.047 lb ai/A (4 to 6 oz/A product)
Time  Apply postemergence to actively growing weeds before they are 3 inches tall or across and the alfalfa has less than 3 inches of regrowth.
Remarks  May be applied to established alfalfa in the fall or winter or in the spring to dormant or semidormant alfalfa or between cuttings. Adding an adjuvant (nonionic surfactant or crop oil concentrate) and a liquid fertilizer or ammonium sulfate solution is required. Weeds under stress are less susceptible to control. Apply at least 1 hour before rain or overhead irrigation
Caution  Do not exceed 6 oz product/A per season. Note recropping restrictions before using. Some crops cannot be planted within 26 mo of application. Only rotational crops harvested at maturity may be used for feed or forage.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Imidazolinone
•  flumioxazin  (Chateau)
Rate  2 oz ai/A (4 oz product/A)
Time  Apply preemergence to the weeds.
Remarks  Applications should be made as soon as possible after cutting and removing alfalfa to minimize crop injury. Flumioxazin will burn treated leaves and stems. A second application can be made 60 days after the first application. Gives only fair control of many annual grasses. Apply with paraquat to burn down weeds when applying after the last harvest in the fall or when alfalfa is dormant.
Caution  Do not apply harvest or graze within 25 days of application. Do not make second application within 60 days of the first application. Do not exceed 8 oz of Chateau during a single growing season.
Site of action  Group 14: protoporphyrinogen oxidase (PPO) inhibitor
Chemical family  N-phenylphthalimide

FORAGE ALFALFA—Dodder Control
•  glyphosate
Rate  0.0625  to 0.075 lb ae/A
Time  Apply as a spot treatment to actively growing dodder in non-Roundup-Ready alfalfa.
Remarks  A properly calibrated sprayer is required to make an accurate application.
Caution  Do not spray more than 10% of the field to be harvested. If applied incorrectly, alfalfa will be injured or killed in treated areas. Do not graze or harvest within 14 days after application.
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
•  pendimethalin (Prowl H2O)
Rate  1.9 to 3.8 lb ai/A ( 2 to 4 quarts/A product)
Time  Apply to established alfalfa between January 15 and April 30 but before dodder germinates.
Remarks  Controls most annual grasses and, in addition to dodder, certain broadleaf weeds as they germinate. For optimum dodder control, use 3 to 4 quarts/A product.
Caution  Do not apply to seedling alfalfa. Do not exceed 4 quarts/A of product per year. Do not harvest for forage or hay for at least 50 days after application. Refer to label for crop rotation restrictions.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
FORAGE ALFALFA—Perennial Weed Control—Quackgrass, Field Bindweed, Canada Thistle, Johnsongrass, etc.
•  glyphosate
Rate  2.25 to 3.75 lb ae/A. For nonsodded quackgrass, use 0.75 to 1.5 lb ae/A. For sodded quackgrass, use 1.5 to 2.25 lb ae/A.
Time  Apply preplant to full-grown weeds at least 10 days before planting the crop or as a spot treatment in the crop. Refer to label for growth stage of perennial weeds.
Remarks  Use highest rate on field bindweed.
Caution  Do not apply if weed is stressed from drought, weather, or maturity. Rain within 6 hr after application may reduce effectiveness. Control weed escapes the following years. If used as a spot treatment in the growing crop, do not treat more than 10% of the field. Do not harvest or graze within 14 days after treatment.
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
FORAGE ALFALFA—Preharvest Weed Control in Declining Alfalfa Stands
•  glyphosate
Rate  Up to 1.5 lb ae/A
Time  Apply when weeds are actively growing prior to last cutting in alfalfa stand where crop destruction is acceptable.
Remarks  Not all glyphosate formulations have this use on the label. Apply to declining alfalfa stands before the last cutting and rotating out of alfalfa. Treated crop and weeds can be fed to livestock. For satisfactory weed control, till deeply after treatment.
Caution  Preharvest interval is 36 hr. Alfalfa will be severely injured or killed. Do not use on alfalfa grown for seed.
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
FORAGE ALFALFA—Other Registered Herbicides
•  MCPA (several trade names)
Remarks  Foliar application in winter to control winter annual broadleaf weeds. Selectivity depends on complete dormancy of alfalfa.

Herbicide Effectiveness on Weeds in Alfalfa

Weed family	trifluralin (Treflan)	benefin (Balan)	EPTC	diuron (Karmex)	terbacil (Sinbar)	metribuzin (Sencor)	hexazinone (Velpar)	norflurazon (Zorial)	pronamide (Kerb)	2,4-DB	paraquat (Gramoxone)	imazethapyr (Pursuit)	bromoxynil (Buctril)	sethoxydim (Poast)	clethodim (Select)	pendimethalin (Prowl H2O)	
Broadleaves 
(Mustard)
Mustard, blue	

P	

P	

P	

G	

P	

G	

E	

—	

F-G	

P	

—	

—	

F-H	

P	

P	

P	
Mustard, tansy	P	P	P	E	E	F-G	E	E	G	E	G	E	G	P	P	P	
Mustard, tumble	P	P	F-G	E	E	E	E	E	G	E	E	E	G	P	P	—	
Mustard, wild	P	P	P	E	E	E	—	—	G	E	—	E	G	P	P	—	
Pennycress, field	P	P	P	E	E	E	E	—	G	—	E	E	—	P	P	—	
Shepherdspurse	P	P	F-G	E	E	E	E	E	G	—	E	E	F-G	P	P	—	
Composite
Cocklebur	
P	
P	
P	
F	
G	
G	
—	
—	
P	
G	
—	
G	
—	
P	
P	
—	
Dandelion	P	P	P	—	F-G	P-F	F-G	—	P	F	F	P	P	P	P	P	
Lettuce, prickly	P	P	P	E	E	E	E	—	P	E	E	P	F	P	P	P	
Sowthistle	P	P	P	G-E	E	G	—	—	P	G	E	P	F-G	P	P	—	
Sunflower	P	P	P	F	G	F-G	—	—	P	G	E	G	—	P	P	—	
Grasses
Barnyardgrass	
E	
E	
E	
E	
E	
G	
—	
E	
E	
P	
E	
F-G	
P	
E	
E	
E	
Brome, downy	E	E	G-E	F	E	G	E	E	E	P	E	P	P	P	P	E	
Foxtail	E	E	E	E	E	G	E	E	E	P	E	F-G	P	E	E	E	
Grain, volunteer	F-G	F-G	G	P-F	F-G	P-F	E	—	G	P	E	P	P	G	G	—	
Oat, wild	F	F	G	P	—	F-G	—	—	F-G	P	F-G	F	P	G	G	G	
Quackgrass	P	P	F-G	P	F	P-F	F	—	G	P	F	P	P	F	F	P	
Sandbur	G	G-E	G-E	G-E	G	G	—	—	E	P	E	—	P	G	G	G	
Miscellaneous
Chickweed	
G	
G	
G	
E	
E	
E	
E	
—	
G	
P	
G	
—	
P	
P	
P	
G	
Dodder	P	P	P	P	P	P	P	P	F-G	P	—	P	—	P	P	E	
Knotweed	G	G	F	P	E	G	—	—	G	P	G	—	F	P	P	G	
Kochia	G-E	G-E	P	E	G-E	G	—	—	F	G-E	G	G	E	P	P	G	
Lambsquarters	G-E	G-E	G	E	E	E	E	F	G	E	E	F	G	P	P	G-E	
Nightshade	P	P	G	—	E	P	—	G	G	G	E	E	G	P	P	F	
Pigweed	G-E	G-E	G	E	E	E	E	F	P	E	E	E	F-G	P	P	G	
Purslane	G	G	G	E	G-E	G	—	—	G	G	E	G	F	P	P	G	
Thistle, Russian	G-E	G	P	G-E	G-E	F-G	—	—	G	E	E	—	G	P	P	—	
E = excellent    G = good     F = fair     P = poor or no control     	(—) = limited information
Response of weeds to any of the listed herbicides may be altered by growing conditions, weed populations, type of irrigation, genetic variations of weeds, soil type, pH, organic matter, time of application, and application rate.  An example is the E rating given for barnyardgrass control with paraquat.  Paraquat will control most annual weeds when they are small, but paraquat is applied in the winter when alfalfa is dormant and summer annual weeds are not growing.  Ratings may vary from season to season and from site to site within the area.  Weed control generally decreases as the season progresses.  See herbicide label for applicability to other weeds.