Alfalfa

Agricultural pest management


Yellow foxtail in alfalfa.

Herbicide Treatment Table for Established 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.
 
PREEMERGENCE (BEFORE WEEDS EMERGE)
 
A. DIURON 1.2–2.4 lb a.i.    
  (Karmex DF) 1.2–2.4 qt 12 0
  (Direx 4L) 1.5–3 lb 12 0
  WSSA MODE-OF-ACTION GROUP NUMBER1: 7
  COMMENTS: Apply after dormancy begins through January, but before weeds are well established. Apply only to stands 1 year or older. Do not replant treated areas within 1 year (2 years if applied over 2 lb/acre). Do not use on coarse soils or in areas where crop does not go dormant. Considered to be a ground water contaminant and requires a use permit within Ground Water Protection Areas.
 
B. EPTC 2–3 lb a.i.    
  (Eptam 7E) 2.25–3.5 pt 12 14 (graze or harvest)
  WSSA MODE-OF-ACTION GROUP NUMBER1: 8
  COMMENTS: Apply in spring before weed emergence. Apply as water-run. Use low rate on sandy soil, high rate on heavy soil. Repeat herbicide applications may be needed, up to 12.25 lb a.i. per season.
 
C. FLUMIOXAZIN 0.1275 lb a.i. 12 25 (graze or harvest)
  (Chateau) 4 oz    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 14
  COMMENTS: Apply to semi-dormant crop. It is most effective on broadleaf weeds and some grasses as a preemergence application. Apply prior to winter weed emergence (September–October) in the low deserts.
 
D. HEXAZINONE 0.495–1.5 lb a.i.    
  (Velpar L CU) 2–6 pt 48 30
  WSSA MODE-OF-ACTION GROUP NUMBER1: 5
  COMMENTS: Apply during alfalfa dormancy. Do not use more than 0.675 lb a.i. on alfalfa less than 1 year old. Do not use on frozen ground or at high rates in high rainfall areas. Hexazinone is persistent in the soil and can injure crops following alfalfa. Follow label directions carefully; observe plantback restrictions.
 
E. METRIBUZIN 0.375–0.9975 lb a.i.    
  (Tricor DF) 0.5–1.33 lb 12 42 (graze or harvest)
  WSSA MODE-OF-ACTION GROUP NUMBER1: 5
  COMMENTS: Apply in fall (during dormancy) or spring before new growth. Use on stands 1 year or older. Use only north of Interstate 80. Do not exceed 1 lb a.i./acre per season. Follow label directions carefully; observe plantback restrictions.
 
F. NORFLURAZON 1–1.965 lb a.i.    
  (Solicam DF) 1.25–2.5 lb 12 28
  WSSA MODE-OF-ACTION GROUP NUMBER1: 12
  COMMENTS: Application may be made to both dormant and actively growing alfalfa. Will not control emerged weeds, only germinating weeds and nutsedge tubers. For 16 months after last application of this herbicide, the only rotational crop that can be planted is cotton. Bioassays are required for all other crops. Considered to be a ground water contaminant and requires a use permit within Ground Water Protection Areas.
 
G. PENDIMETHALIN 1.9–3.8 lb a.i.    
  (Prowl H2O) 2–4 qt 24 See comments
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Apply before dodder and grass germination. Higher rates applied in January through February provide long season grass control into late summer (August). PHI is 50 days for forage or hay and 90 days for seed.
 
H. TRIFLURALIN 2 lb a.i.    
  (Treflan TR-10) 20 lb 12 21
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Apply before dodder and grass germination. Requires 0.5 inch rain or irrigation water within 3 days after an herbicide application. One application controls dodder into June; for longer control apply again after the first or second cutting.
 
POSTEMERGENCE (After Weeds Emerge)
 
A. 2,4-DB* 0.5–1.5 lb a.i.    
  (Butyrac 200) 1–3 qt 48 30 (graze or feed)
  WSSA MODE-OF-ACTION GROUP NUMBER1: 4
  COMMENTS: Apply when weeds are 3 inches or shorter. Rate varies with formulation and weed size. See label for grazing restrictions and regulatory restrictions for sensitive cropping areas. Apply when temperature is between 40°–90°F. Treated area should not receive irrigation or rainfall within 4 days. Restricted use from Mar 15 through Oct 15 in some Central Valley counties; check with your county agricultural commissioner.
 
B. CARFENTRAZONE 0.008–0.04 lb a.i.    
  (Shark EW) 0.5–2.5 fl oz 12 21 (forage or hay)
  WSSA MODE-OF-ACTION GROUP NUMBER1: 14
  COMMENTS: Can be applied during the dormant period in winter or in season between cuttings for post emergence broadleaf weeds. In season application may result in a yield decrease between cuttings. Oil adjuvant will enhance herbicide activity.
 
C. CLETHODIM 0.091–0.2425 lb a.i.    
  (Select Max) 12–32 fl oz 24 15 (graze or feed)
  WSSA MODE-OF-ACTION GROUP NUMBER1: 1
  COMMENTS: Do not apply within 15 days of grazing or harvest. For control of annual grasses use a minimum of 17 oz. Apply only to actively growing grasses at the height recommended on label. Use higher rate for perennial grasses, annual bluegrass, and under heavy grass pressure.
 
D. GLYPHOSATE (Roundup Ready alfalfa only)      
  (Roundup Powermax) Label rates 4 5
  WSSA MODE-OF-ACTION GROUP NUMBER1: 9
  COMMENTS: In Roundup Ready alfalfa 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. HALOSULFURON 0. 0312–0.0468 lb a.i.    
  (Sandea) 0.667–1 oz 12 14
  WSSA MODE-OF-ACTION GROUP NUMBER1: 2
  COMMENTS: Effective for postemergence control of nutsedge in established alfalfa. Can cause temporary stunting and yellowing of crop when applied during growing season in Sacramento and San Joaquin valleys. Less injury and yield loss results following applications in low desert region of California; crop injury is minimal and weed control best when applied in late summer (August–October) in the low deserts.
F. HEXAZINONE 0.45–1.35 lb a.i    
  (Velpar) 2–6 pt 48 30
  WSSA MODE-OF-ACTION GROUP NUMBER1: 5
  COMMENTS: Weeds must be smaller than 2 inches tall or wide and receive 0.5 inch rainfall or irrigation to be effective post emergence. Do not use on alfalfa under stress. Use on dormant or slowly growing, healthy plants.
 
G. IMAZAMOX 0.031–0.047 lb a.e. 4 0
  (Raptor) 4–6 fl oz    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 2
  COMMENTS: Has the same mode of action as imazethapyr, and it is not recommended that these two products be applied alternately. A systemic herbicide with short soil residual that controls broadleaf and grass weeds postemergence. 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, and fiddleneck but can be tank mixed with another herbicide to broaden the spectrum of weeds controlled and soil residual time. Some useful tank mix options are hexazinone, flumioxazin, and pendimethalin.
 
H. IMAZETHAPYR 0.047–0.094 lb a.i.    
  (Pursuit) 3–6 oz 4 30 (graze, feed, or harvest)
  WSSA MODE-OF-ACTION GROUP NUMBER1: 2
  COMMENTS: Apply when the weeds are 1 to 3 inches. Do not apply 12 months before the alfalfa is taken out of production because of plantback restrictions. Add a nonionic surfactant (0.25% v/v) or a crop oil concentrate (2 pt/acre). During winter months under cold conditions, use the highest label rate. Pursuit has postemergence and preemergence activity. Soil residual activity is considerably long (e.g., sugarbeets cannot be planted for 40 months). Postemergence herbicide activity is generally slow, up to 50 days. Use resistance management practices (i.e., alternate use with an herbicide of different chemistry).
 
I. PARAQUAT*
  (Gramoxone SL 2.0) Label rates 12 See label
  WSSA MODE-OF-ACTION GROUP NUMBER1: 22
  COMMENTS: Can be applied during dormant period in winter, rates vary depending on weed growth stage, crop leaf burn will occur but recovery is rapid. Gramoxone is commonly tank mixed with a soil residual herbicide to broaden the weed spectrum and increase the length of control. See label for grazing restrictions. Always use a nonionic surfactant with paraquat. Do not apply more than once per season.
 
J. SAFLUFENACIL 0.022–0.044 lb a.i    
  (Sharpen) 1–2 fl oz 12 See label
  WSSA MODE-OF-ACTION GROUP NUMBER1: 14
  COMMENTS: Used during the winter dormant period for emerged broadleaf weeds. Can be tank mixed with other post or pre emergence herbicides. Application timing should allow at least 75 days before first harvest. Oil adjuvant is required.
 
K. SETHOXYDIM 0.1–0.46 lb a.i.    
  (Poast) 1–2.5 pt 12 See comments
  WSSA MODE-OF-ACTION GROUP NUMBER1: 1
  COMMENTS: Apply when grass weeds have emerged but are still small. Add oil concentrate at 2 pint/acre. Irrigate before application or 2 days after. Preharvest interval is 7 days for grazing, feeding, or cutting for undried forage; 14 days for cutting for dry hay.
 
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.
* Permit required from county agricultural commissioner for purchase or use.
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.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430

Weeds for Established Alfalfa

W. M. Canevari, UC Cooperative Extension, San Joaquin County
S. B. Orloff, UC Cooperative Extension, Siskiyou County
W. T. Lanini, Weed Science/Plant Sciences, UC Davis
R. G. Wilson, UC Cooperative Extension, Lassen County
R. N. Vargas, UC Cooperative Extension, Madera County

Acknowledgment for contributions to Weeds:
C. E. Bell, UC Cooperative Extension, San Diego County
R. F. Norris, Vegetable Crops/Weed Science, UC Davis
J. L. Schmierer, UC Cooperative Extension, Colusa County

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