How to Manage Pests

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.
PREPLANT
Before Weeds Emerge
A.	DIURON	1.2–2.4 lb a.i.	12	0
	(Karmex DF, Direx 4L)
	WSSA MODE OF ACTION GROUP NUMBER1: 7
	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.
B.	NORFLURAZON	1–1.965 lb a.i.	12	28
	(Solicam) DF
	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 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.
C.	EPTC	2–3 lb a.i.	12	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.
D.	HEXAZINONE	0.495–1.5 lb a.i.	48	30
	(Velpar)
	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 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.
E.	METRIBUZIN	0.375–0.9975 lb a.i.	12	28 - graze/harvest
	(Sencor)
	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/season. Follow label directions carefully; observe plantback restrictions.
F.	FLUMIOXAZIN	0.1275 lb a.i.	12	25 – graze/harvest
	(Chateau)	4 oz
	WSSA MODE OF ACTION GROUP NUMBER1: 14
	COMMENTS: Apply to semi-dormant crop.
G.	PENDIMETHALIN	1.9–3.8 lb a.i.	24	see comments
	(Prowl H2O)	2–4 qt
	WSSA MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: Higher rates applied in Jan-Feb 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.	12	21
	(Treflan TR-10)
	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 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)
A.	GLYPHOSATE	0.9453–1.89 lb a.i.
	(Roundup WeatherMax)	22–44 fl oz	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/year.
Conventional and Roundup-ready Alfalfa
A.	HEXAZINONE	0.45–1.35 lb a.i	48	30
	(Velpar)
	WSSA MODE OF ACTION GROUP NUMBER1: 5
	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.
B.	PARAQUAT*	0.26–0.49 lb a.i.	24	60–cut/harvest
	(Gramoxone Inteon)
	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. See label for grazing restrictions. Always use a nonionic surfactant with paraquat. Do not apply more than once per season.
C.	SETHOXYDIM	0.1–0.46 lb a.i.	12	see comments
	(Poast)
	WSSA MODE OF ACTION GROUP NUMBER1: 1
	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.
D.	2,4-DB*	0.5–1.5 lb a.i.	48	30–graze/feed/harvest
	(Butyrac 200)
	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 - Oct 15 in some Central Valley counties; check with your County Agricultural Commissioner.
E.	IMAZETHAPYR	0.047–0.094 lb a.i.	4	30–graze/feed/harvest
	(Pursuit)
	WSSA MODE OF ACTION GROUP NUMBER1: 2
	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).
F.	CLETHODIM	0.095–0.2425 lb a.i.	24	15–graze/feed/harvest
	(Select Max)
	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.
G.	HALOSULFURON	0. 0312–0.0468 lb a.i.	12	14
	(Sandea)	0.667–1 oz
	WSSA MODE OF ACTION GROUP NUMBER1: 2
	COMMENTS: Effective for postemergent 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 reaults following applications in low desert region of California.
+	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 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. For more information, see http://www.hracglobal.com.

PUBLICATION

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

Top of page