UC IPM: Information about Herbicides for Established Alfalfa

UC Pest Management Guidelines

Common name

Amount/Acre

R.E.I.+

P.H.I.+

(trade name)

(hours)

(days)

When choosing an herbicide, consider the environmental impact.

Before Weeds Emerge

DIURON

1.2–2.4 lb a.i.

(Karmex DF, Direx 4L or 80DF)

MODE OF ACTION: A urea (Group 7)¹ herbicide.

COMMENTS: Restricted entry interval: 12 hours. Apply after dormancy begins until January, but before weeds are well established. Treat only stands 1 year or older. Do not replant treated areas within 1 year (2 yr if 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.

NORFLURAZON

1–2 lb a.i.

(Zorial) 5G

MODE OF ACTION: A pyridazinone (Group 12)¹ herbicide.

COMMENTS: Application may be made to both dormant and actively growing alfalfa. Will not control emerged weeds, only germinating weed seed and nutsedge tubers. For 16 months after last application of this material 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.

EPTC

2–3 lb a.i.

14 - graze/harvest

(Eptam) 7EC

MODE OF ACTION: A thiocarbamate (Group 8)¹ herbicide.

COMMENTS: Apply in spring before weed emergence. Must be mechanically incorporated or apply as water-run. Use low rate on sandy soil, high rate on heavy soil. Repeat treatments may be needed, up to 12.25 lb a.i./season.

HEXAZINONE

0.495–1.5 lb a.i.

(Velpar)

MODE OF ACTION: A triazinone (Group 5)¹ herbicide.

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 in low desert valleys, 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.

METRIBUZIN

0.375–1 lb a.i.

28 - graze/harvest

(Sencor)

MODE OF ACTION: A triazinone (Group 5)¹ herbicide.

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/season. Follow label directions carefully; observe plantback restrictions.

TRIFLURALIN

2 lb a.i.

(Treflan TR-10)

MODE OF ACTION: A dinitroaniline (Group 3)¹ herbicide.

COMMENTS: Apply before dodder and grass germination. Requires 0.5 inch rain or irrigation water within 3 days after treatment. One application controls dodder into June; for longer control apply again after the first or second cutting.

After Weeds Emerge (Roundup-ready alfalfa only)

GLYPHOSATE

0.9453-1.89 lb a.i.

(Roundup WeatherMax)

22–44 fl oz

MODE OF ACTION: A glycine (Group 9)¹ herbicide.

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/year.

Conventional and Roundup-ready Alfalfa

HEXAZINONE

0.45–1.35 lb a.i

(Velpar)

MODE OF ACTION: A triazinone (Group 5)¹ herbicide.

COMMENTS: Weeds must be smaller than 2 inches tall or wide. Do not use on alfalfa under stress. Use on dormant or slowly growing, healthy plants.

PARAQUAT*

0.26–0.49 lb a.i.

60 - cut/harvest

(Gramoxone Max)

MODE OF ACTION: A bipyridylium (Group 22)¹ herbicide.

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. See label for grazing restrictions. Always use a nonionic surfactant with paraquat. Do not apply more than once per season.

SETHOXYDIM

0.1–0.46 lb a.i.

see comments

(Poast)

MODE OF ACTION: A DIM (Group 1)¹ herbicide.

COMMENTS: Apply when grass weeds have emerged but are still small. Add oil concentrate at 2 pt/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.

2,4-DB*

0.5–1.5 lb a.i.

30 – graze/feed/harvest

(Butyrac 200)

MODE OF ACTION: A phenoxy-carboxylic-acid (Group 4)¹ herbicide.

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 - Oct 15 in some Central Valley counties; check with your County Agricultural Commissioner.

IMAZETHAPYR

0.047–0.094 lb a.i.

30 – graze/feed/harvest

(Pursuit)

MODE OF ACTION: An imidazolinone (Group 2)¹ herbicide.

COMMENTS: Apply when the weeds are 1–3 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 postemergent and preemergent activity. Soil residual activity is considerably long (e.g., sugarbeets cannot be planted for 40 months). Postemergent herbicide activity is generally slow, up to 50 days. Use resistance management practices (i.e., alternate use with an herbicide of different chemistry).

CLETHODIM

0.095–0.25 lb a.i.

15 – graze/feed/harvest

(Prism)

MODE OF ACTION: A DIM (Group 1)¹ herbicide.

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.

+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment until the field can be grazed or cut. In some cases the R.E.I. exceeds the P.H.I.; the longer of these two intervals is the minimum time that must elapse before harvest may take place.
*	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. For more information, see http://www.plantprotection.org/HRAC/.

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 the weeds section:
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

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See How to manage pests, or in the U.S., contact your local Cooperative Extension office for assistance. /PMG/r1700311.html revised: November 30, 2006. Contact webmaster.

How to Manage Pests

UC Pest Management Guidelines

Alfalfa

Herbicide Treatment Table for Established Alfalfa

PUBLICATION