Hypera postica
Pest description and crop damage Larvae are about 0.375 inch long, yellow to green, with a white stripe down the back. They feed in and on the buds of alfalfa.
Sampling and thresholds Treat when 20 to 30% of plant terminals show feeding damage - or - when larval populations reach 20 or more per half-circle (180° sweep). These thresholds are simply guidelines to help growers determine when to treat. Weather, plant vigor, irrigation schedules, history of weevils in the area, and a complex of factors may determine whether treatment is justified. In specific geographic areas we have been observing resistance to pyrethroid insecticides, specifically lambda-cyhalothrin. We have also observed increase tolerance to chloropyrifos and pyrethroids, specifically lambda-cyhalothrin in alfalfa weevil populations in select geographic areas, but we have no populations that can survive exposure to labeled rates of chlorpyrifos. Resistance management strategies detailed in insecticide labels should be followed to help reduce the risk of further insecticide resistance development.
Management-chemical control
- Beauveria bassiana strain GHA (BotaniGard, BoteGHA) at 0.11 to 0.44 lb ai/A. PHI 0 days. This product is potentially pathogenic to honeybees. Avoid applying to areas where honeybees are actively foraging or around beehives. Drift and runoff may be hazardous to aquatic organisms in water adjacent to treated areas. Typically, it takes 7 to 10 days after the first spray to see control. Apply at 5- to 10-day intervals for low to normal pest pressure. For high pest pressure, especially aphids, apply at 2- to 5-day intervals. Repeat applications for as long as pest pressure persists. There is no limit on the number of applications or total amount of product that can be applied in one season.
- carbaryl (Carbaryl 4L) at 1 to 1.5 lb ai/A. Not effective against adult alfalfa weevil. REI 12 hr. On dense growth, apply in 25 to 40 gal water per acre with ground equipment to ensure adequate coverage. Extremely toxic to aquatic invertebrates and bees. Notify beekeepers within 1 mile of treatment area. PHI 7 days. Do not exceed 1.5 qt per acre per cutting. It may cause temporary bleaching of tender alfalfa foliage. Labeled for Idaho.
- chlorpyrifos (Chlorpyrifos 4E-AG) at 0.5 to 1 lb ai/A. REI 24 hr. Application rates will vary depending on the nozzle droplet type. Toxic to fish, aquatic invertebrates, small mammals and birds. Highly toxic to bees. Buffer zones must be utilized for aquatic areas when using ground boom (25 ft), chemigation (25 ft), orchard airblast (50 ft), and aerial (150 ft). Do not cut or graze alfalfa within 7 days after application of 0.5 pint/A, 14 days after application of 1 pint, and 21 days after application of > 1 pint/A. Labeled for Idaho.
- dimethoate (400EC, Dimate 4E) at 0.25 to 0.5 lb ai/A. PHI 10 days. REI 48 hr. For suppression only. Do not apply if crop or weeds are in bloom. Effective only on cutting to which chemical is applied. Do not feed or graze livestock. Do not apply more than once per cutting cycle and more than three times per year. Minimum retreatment intervals of 30 days.
- gamma-cyhalothrin (Drexel L-C) at 0.01 to 0.015 lb ai/A. PHI 1 day for forage, 7 days for hay. REI 24 hr. Do not exceed 0.06 lb ai/A per season or 0.015 lb ai/A per cutting. Do not apply on ground within 25 ft of aquatic habitat, 150 ft if applied by air, or 450 ft if applied from ULV. Toxic for bees.
- indoxacarb (Steward EC) at 0.065 to 0.11 lb ai/A. PHI 7 days. REI 12 hr. This is a broad-spectrum insecticide so it should be applied with caution. Make no more than one application per season. Do not apply more than 11.3 fl oz per cutting and more than 45 fl oz per crop season. Do not apply when bees are in the area. Chemigation applications through center pivot is permitted. Labeled for Oregon only.
- lambda-cyhalothrin + chlorantraniliprole (Besiege) at 0.03 to 0.06 lb ai/A. PHI 1 day for forage and 7 days for hay. Do not exceed a total of 31.0 fl oz per year. Do not apply more than 10.0 fl oz/A per cutting and no more than 1 application per cutting. Avoid application when bees are actively foraging by applying during the early morning or during the evening hours. It may be advisable to remove bee shelters during and for 2 to 3 days following application. Avoid direct application to bee shelters.
- lambda-cyhalothrin (Serpent 1EC, Warrior II) at 0.02-0.03 lb ai/A. PHI 1 day for forage, 7 days for hay. REI 24 hr. Do not apply more than 0.03 lb ai (3.84 fl oz or 0.24 pint of product) per acre per cutting, or more than 0.12 lb ai (15.36 fl oz or 0.96 pint of product) per acre per season. Do not apply on ground within 25 ft of aquatic habitat (groundboom, overhead chemigation, or airblast), 150 ft if applied by air, or 450 ft if applied from ULV. Do not apply while bees are active. Advisable to move bee shelters for 2 to 3 days after application. Avoid application when bees are actively foraging by applying during the early morning or during the evening hours.
- permethrin (Arctic) at 0.1 to 0.2 lb ai/A. PHI 0 days at rates equal to or less than 0.1 lb ai/A, 30 days for rates greater than 0.1 lb ai/A or more. REI 12 hr. Do not exceed 0.2 lb ai/A per cutting. If used during bloom, remove bees from field for 3 days. Do not apply on ground within 25 ft of aquatic habitat, 100 ft if applied by air, or 450 ft if applied from ULV.
- zeta-cypermethrin (Mustang Max) at 0.014 to 0.025 lb ai/A. PHI 3 days for cutting or grazing, 7 days for harvest. REI 12 hr. Allow at least 7 days between applications. Do not exceed 0.05 lb ai/A per cutting or 0.15 lb ai/A per year. Do not apply on ground within 25 ft of aquatic habitat, 150 ft if applied by air, or 450 ft if applied from ULV.