Alfalfa

Agricultural pest management


Yellow foxtail in alfalfa.

Herbicide Treatment Table for Seedling Alfalfa

(Reviewed 3/17, updated 3/17)

In this Guideline: More about weeds in alfalfa:

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are listed alphabetically. When choosing a pesticide, consider information relating to environmental impact, resistance management, the pesticide's properties, and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
 
PREPLANT
 
After weeds emerge
 
A. GLYPHOSATE
  (Roundup PowerMax) Label rates 4 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 9
  COMMENTS: In conventional alfalfa, apply any time before planting to kill existing weeds. No soil residue. Do not mow or till before application. Do not apply just before rain or irrigation. High rate for annuals is only suggested for filaree control.
 
B. PARAQUAT* 0.125–0.5 lb a.i.    
  (Gramoxone SL 2.0) 0.5–2 pt 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 22
  COMMENTS: Apply to emerged weeds. Do not use in soils that lack clay minerals, i.e., peat, muck, or pure sand. See label for use restrictions based on county or region. Always use a nonionic surfactant or crop oil concentrate with paraquat.
 
C. PELARGONIC ACID
  (Scythe) 3–10% volume/volume 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 27
  COMMENTS: A nonselective contact herbicide for control of emerged weeds. Can be used any time before alfalfa emergence. Weed size and growth stage determine the rate needed for control; will not control established perennials. This herbicide can also be used during winter dormancy to control winter weeds but cool weather reduces its efficacy. Because this is a contact herbicide, good spray coverage is essential for satisfactory weed control.
 
POSTPLANT
 
A. 2,4-DB* 0.5–1.5 lb a.i.    
  (Butyrac 200) 1–3 qt 48 60
  WSSA MODE-OF-ACTION GROUP NUMBER1: 4
  COMMENTS: A foliar-applied systemic herbicide that has no soil residual. Apply when alfalfa is in the second trifoliolate leaf stage. Broadleaf weeds should be 3 inches or less. Weed control increases with clear and warm conditions. If significant rainfall or irrigation occurs before 4 days after application, crop injury may occur. Can be combined with sethoxydim (Poast), clethodim (Select Max), bromoxynil (Buctril), imazethapyr (Pursuit), or imazamox (Raptor). When mixed with herbicide requiring an adjuvant, nonionic surfactants have shown to be less crop injurious than oil concentrates. Restricted use from Mar 15 to Oct 15 in some Central Valley counties. Check with your county agricultural commissioner. Alfalfa injury symptoms: leaf narrowing and plant twisting. Weed symptoms: twisting, epinasty and chlorosis in 2 to 10 days.
 
B. BROMOXYNIL 0.25–0.375 lb a.i.    
  (Buctril) 0.5–0.75 pt 24 30 (spring alfalfa)
60 (fall and winter alfalfa)
  WSSA MODE-OF-ACTION GROUP NUMBER1: 6
  COMMENTS: A contact herbicide that has no soil residual. Apply when alfalfa is in the second trifoliolate leaf stage. Broadleaf weeds should be 2 inches or less. Thorough coverage is essential for best control. Do not apply when temperatures exceed 80°F. Combining with sethoxydim (Poast), clethodim (Select Max), imazethapyr (Pursuit), imazamox (Raptor), or 2,4-DB(Butyrac) will broaden control. When combined with the herbicides requiring oil adjuvants, crop injury will increase. Nonionic surfactants have shown to be less injurious to crop than oil concentrates. Alfalfa injury symptoms: leaf burn. Weed symptoms: browning and necrosis within 2 to 4 days.
 
C. CLETHODIM 0.068–0.2425 lb a.i.    
  (Select Max) 9–32 fl oz 24 15
  WSSA MODE-OF-ACTION GROUP NUMBER1: 1
  COMMENTS: A systemic herbicide with no soil residual. Apply when alfalfa is in the first trifoliolate leaf stage. Control is best when alfalfa is in the 3rd trifoliolate leaf stage and grass weeds are between 2 to 6 inches tall, growing vigorously before tillers develop. Control is reduced when grasses are moisture-stressed. Oil adjuvant or nonionic surfactant is required (see label for specific requirements). Can be combined with bromoxynil (Buctril), 2,4-DB (Butyrac), imazethapyr (Pursuit), and imazamox (Raptor) herbicides. Oil concentrate adjuvant will increase crop injury when mixed with bromoxynil (Buctril) or 2,4-DB (Butyrac). Alfalfa injury symptoms: none observed. Weed symptoms: chlorosis followed by necrosis at growing point in 6 to 10 days.
 
D. GLYPHOSATE (Roundup Ready alfalfa only)
  (Roundup Powermax) Label rates 4 5
  WSSA MODE-OF-ACTION GROUP NUMBER1: 9
  COMMENTS: In Roundup Ready varieties, over-the-top applications can be made at any stage of growth. Do not use more than 132 fl oz/acre per year.
 
E. HEXAZINONE 0.25–0.375 lb a.i    
  (Velpar L CU) 1–1.5 pt 48 30
  WSSA MODE-OF-ACTION GROUP NUMBER1: 5
  COMMENTS: A contact herbicide that also has soil residual. Use caution on sandy soil. Apply when alfalfa is between the sixth to ninth trifoliolate leaf stage with multiple stems, and root length is greater than 6 inches. Has both pre- and postemergence activity on small broadleaf weeds less than 2 inches in size. See label for additional restrictions. Useful tank mixes include sethoxydim (Poast) and clethodim (Select Max). Alfalfa injury symptoms: leaf burn and chlorosis. Weed symptoms: chlorosis and necrosis in 1 to 2 weeks.
 
F. IMAZAMOX 0.032–0.047 lb a.i.    
  (Raptor) 4–6 fl oz 4 0
  WSSA MODE-OF-ACTION GROUP NUMBER1: 2
  COMMENTS: A systemic herbicide with soil residual that controls broadleaf and grass weeds. Has the same mode of action as imazethapyr (Pursuit), and it is not recommended that these two products be applied alternately. Apply when alfalfa is at least in the second trifoliolate leaf stage. Control is best when broadleaf weeds and grass weeds are less than 3 inches in height and growing vigorously. Control is reduced when weeds are moisture-stressed. Does not adequately control prickly lettuce, annual sowthistle, lambsquarters, and fiddleneck but can be tank mixed with another herbicide to broaden the spectrum of weeds controlled. Must use an adjuvant and a nitrogen-based fertilizer additive such as ammonium sulfate or urea ammonium nitrate (UAN). Useful tank mixes include bromoxynil (Buctril) and 2,4-DB (Butyrac). Oil adjuvants will increase the potential of crop injury when used with bromoxynil (Buctril) or 2,4-DB (Butyrac). Using a nonionic surfactant may be a safer choice. Alfalfa injury symptoms: temporary growth reduction. Weed symptoms: chlorosis followed by necrosis in 1 to 2 weeks.
 
G. IMAZETHAPYR 0.047–0.094 lb a.i.    
  (Pursuit) 3–6 oz 4 30
  WSSA MODE-OF-ACTION GROUP NUMBER1: 2
  COMMENTS: A systemic herbicide with soil residual. Apply when alfalfa is at least in the second trifoliolate leaf stage. Control is best when broadleaf weeds and some grass weeds are less than 3 inches in height and growing vigorously. Weed control is greatly reduced when plants are moisture stressed. Can be combined with sethoxydim (Poast), clethodim (Select Max), bromoxynil (Buctril), imazamox (Raptor), or 2,4-DB (Butyrac) herbicides. Oil adjuvants will increase the potential of crop injury when used with bromoxynil (Buctril) or 2,4-DB (Butyrac). Using a nonionic surfactant may be a safer choice. Alfalfa injury symptoms: temporary growth reduction. Weed symptoms: chlorosis followed by necrosis in 1 to 2 weeks.
 
H. PARAQUAT* 0.125–0.5 lb a.i.    
  (Gramoxone SL 2.0) 0.5–2 pt 12 70
  WSSA MODE-OF-ACTION GROUP NUMBER1: 22
  COMMENTS: A contact herbicide that has no soil residual. Due to risk of crop injury, use only as a rescue treatment when other options have failed. Apply when alfalfa is in the third trifoliolate leaf stage or later. Broadleaf weeds should be between 1 to 3 inches and grasses below 6 inches. Thorough coverage is essential for best control. Rate increases with larger alfalfa plant size: use the 8 fl oz rate (0.125 lb a.i.) if alfalfa has at least 3 trifoliate leaves and 12.8 fl oz (0.2 lb a.i.) if alfalfa has 6 trifoliate leaves. Tank mixing information with other herbicides is limited. Always use a nonionic surfactant or crop oil concentrate. Alfalfa injury symptoms: leaf bleaching to browning. Stand reduction on smaller seedlings. Weed symptoms: bleaching and necrosis in 1 to 3 days.
 
I. SETHOXYDIM 0.09-0.46875 lb a.i.    
  (Poast) 0.5–2.5 pt 12 See label
  WSSA MODE-OF-ACTION GROUP NUMBER1: 1
  COMMENTS: A systemic herbicide that has no soil residual. Can be applied when alfalfa is in the first trifoliolate leaf stage. Control is best when alfalfa is in the 3rd trifoliolate leaf stage and grass weeds are between 2-6 inches tall, growing vigorously before tillers develop. Control is reduced when grasses are moisture-stressed. Oil adjuvant is required. Can be combined with bromoxynil (Buctril), 2,4-DB (Butyrac), imazethapyr (Pursuit), and imazamox (Raptor) herbicides. Oil concentrate adjuvant will increase crop injury when mixed with bromoxynil (Buctril) or 2,4-DB (Butyrac). Alfalfa injury symptoms: none observed. Weed symptoms: chlorosis followed by necrosis at growing point in 6 to 10 days.
 
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1 Group numbers are assigned by the Weed Science Society of America (WSSA) according to different modes of action. Although weeds may exhibit multiple resistance across many groups, mode-of-action numbers are useful in planning mixtures or rotations of herbicides with different modes of action.
NA Not applicable
* Permit required from county agricultural commissioner for purchase or use.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430

Weeds for Seedling Alfalfa

W. M. Canevari, UC Cooperative Extension, San Joaquin County (Emeritus)
S. B. Orloff, UC Cooperative Extension, Siskiyou County
D. H. Putnam, Plant Sciences, UC Davis

Acknowledgment for contributions to Weeds:
C. E. Bell, UC Cooperative Extension, San Diego County (Emeritus)
W. T. Lanini, Weed Science and Plant Sciences, UC Davis (Emeritus)
R. F. Norris, Vegetable Crops and Weed Science, UC Davis (Emeritus)
J. L. Schmierer, UC Cooperative Extension, Colusa County (Emeritus)
R. N. Vargas, UC Cooperative Extension, Madera County (Emeritus)
R. G. Wilson, Intermountain Research & Extension Center

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