Alfalfa Seed

Alfalfa Weevil

Sue Blodgett

Alfalfa weevil adult, left; larva, right.

 

Alfalfa weevil is the most destructive insect of forage alfalfa in the intermountain western region of the United States and also infests alfalfa grown for seed.  The larvae feed on developing leaves within plant terminals and on expanded leaves.  Terminals can be damaged and even killed by alfalfa weevil larvae feeding, damaging or delaying flower formation and therefore seed set.  Information about life history and biology can be found in the alfalfa chapter http://highplainsipm.org/HpIPMSearch/Docs/AlfalfaWeevil-Alfalfa.htm   However, management of alfalfa weevil for seed producers is different than for forage producers because they are constrained by need to protect pollinators.  Pre-bloom or cover sprays, applied prior to placing leafcutter shelters in the field typically target alfalfa weevil, lygus bug and pea aphids. 

Pollinators

The alfalfa leafcutter bee, Megachile rotundata, is the most important pollinator of alfalfa for commercial seed production in the western United States.  The bee was first imported into Canada in 1962.  Growers either culture the bees themselves or hire a pollinating service.  Bees are placed in the field to maximize seed set and to allow sufficient time for bee reproduction.  In many cases producers derive income from both seed crop and from sales of bees over what is needed for next year’s pollination.  

See Alfalfa Weevil for applications made prior to bees being placed in field.

Product List for Alfalfa Weevil:

Insecticide

Lbs Active Ingredient per Acre (Fl oz. or oz. product)

Preharvest Interval, remarks

Furadan 4FR

0.5 - 2 pts

7-28 days depending on rate. 24 hrs REI. 1 application/season. Extremely Hazardous to Bees! Do not apply to alfalfa in bloom. Check label for other restrictions.

chlorpyrifos 4ER,1,2

16 – 32

14 days (1 pt), 21 days (over 1 pt rate). 24 hr REI. Do not make more than 4 applications/year or more than one application per cutting. Extremely Hazardous to Bees! Do not apply when bees are present. Minor phytotoxicity may occur on rapidly growing foliage.

Imidan 70W

1-1.33 lb

7 days. 24 hr REI. 1 application/ cutting. Extremely Hazardous to Bees!  Do not apply to alfalfa in bloom. Buffer spray solution to maintain  pH 7 or lower for best activity.

Lannate SP, LVR,2

16 (SP)

48 (LV)

7 days to graze or feeding. 48 hr REI. Do not apply more than 3.6 lbs ai /season. Do not make more than 10 applications per crop. Extremely Hazardous to Bees!  Do not apply to alfalfa in bloom.

lambda cyhalothrinR,1,2

2.56-3.84

7 days for hay. 24 hr REI.  Extremely Hazardous to Bees!  Do not apply to alfalfa in bloom. Do not apply more than 0.24 pt /A per cutting.  Do not apply more than 0.96 pt/A per season.  Advisable to move bees during application and allow 3 (low rate) or 5 (high rate) days before re-introduction of bees

malathion2

See labels

0 days. 12 hr REI.  Not effective below 65oF. Apply to blooming alfalfa only in evening or early morning when bees are not working.

Mustang 1.5E, MAXR,1

2.2– 4 oz

3 days.  12 hr REI. Extremely Hazardous to Bees!  Do not apply to alfalfa in bloom. No more than 4 oz per cutting, 12 oz per season

permethrin

See labels

1 day if less than 0.1 lb ai/A. 14 days at rates greater than 0.1 lb ai. 12 hr REI. Do not apply more than 0.2 lb ai per cutting.  Extremely Hazardous to Bees!  Do not apply to alfalfa in bloom.

ProaxisR,1

2.56-3.84

7 days for hay. 24 hr REI. Extremely Hazardous to Bees!  Do not apply to alfalfa in bloom. Do not apply more than 0.24 pt /A per cutting.  Do not apply more than 0.96 pt/A per season.  Advisable to move bees during application and allow 3 (low rate) or 5 (high rate) days before re-introduction of bees

R Restricted Use Pesticide 1 Labeled for chemigation  224c labels may be available, check with State Dept of Agriculture. 3Several formulations.

Additional chemicals for which Special Labels (Section 24c or 18’s) are available include: Capture 2EC, Supracide 2E. 

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.

 

 

Categories: Alfalfa Seed, Insects, Alfalfa weevil

Date: 11/17/2006