1. Insect
  2. Legume, Grass, and Field Seed Crops
  3. Pests of Alfalfa Grown for Seed

Alfalfa seed-Aphid

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Includes

Alfalfa aphid (Macrosiphum creelii)
Blue alfalfa aphid (Acyrthosiphon kondoi)
Pea aphid (Acyrthosiphon pisum)
Spotted alfalfa aphid (Therioaphis maculata)

Pest description and crop damage Pea and alfalfa aphids are the common light-green aphids found on stems in the upper canopy. Aphids feed on plant sap. Large numbers can stress and yellow alfalfa. Blue alfalfa aphid causes less damage than pea aphid. Spotted alfalfa aphid is small and yellow to brown with red bumps on its back. It secretes much honeydew and injects toxins that injure some varieties. It is a hot weather aphid population that typically increases as other aphids decline and is very difficult to control. Spray at ground with at least 25 gal/A water. Damage is most severe on seedling stands.

Sampling and thresholds Control the pea aphid in alfalfa grown for seed if populations approach 100 per sweep, the plants are less than 1 foot high, the field is under water stress, and aphid populations show no sign of leveling off. If blue alfalfa aphid has been confirmed in the area and fields have been damaged, treat when numbers reach 30 per sweep. Begin scouting for spotted alfalfa aphid in late June or early July. In established stands, treat when spotted aphids average 20 to 30 per stem, or 50 per sweep, and the population is increasing.

Management-chemical control

  • dimethoate 400 EC at 0.25 to 0.5 lb ai/A. PHI 10 days. REI 48 hr. For suppression of alfalfa weevil only. Do not apply if crop or weeds are in bloom. Do not feed or graze livestock.
  • flonicamid (Beleaf) at 0.089 lb ai/A. REI 0 hr. Do not apply more than twice a season. Apply in a minimum of 3 gpa by air or 10 gpa by ground. This is the preferred insecticide during the bloom period due to safety for pollinators.
  • gamma-cyhalothrin (Proaxis, Declare) 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.
  • lambda-cyhalothrin (Warrior) at 0.02 to 0.03 lb ai/A. PHI 1 day for forage, 7 days for hay. REI 24 hr. Do not apply on ground within 25 ft of aquatic habitat, 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.
  • malathion 8EC at 0.75 to 1 lb ai/A. PHI 0 days. REI 12 hr. Not effective below 65ºF. WA only.
  • permethrin at 0.05 to 0.2 lb ai/A. PHI 0 days at rates equal to or less than 0.1 lb ai/A, 14 days at rates greater than 0.1 lb ai/A. REI 12 hr. Do not reapply at less than 7-day intervals or exceed 0.2 lb ai/A per cutting. If used during bloom, remove bees from field for 3 days.
  • pymetrozine (Fulfill) at 0.086 lb ai/A when aphids first appear. PHI 14 days. Do not exceed 0.086 lb ai/A per cutting or 0.17 lb ai/A per season. Can be toxic to bees. SLN ID000010; WA000016; OR040005.
  • sulfoxaflor (Transform WG) at 0.023 to 0.031 lb ai/A. PHI 7 days for harvest. Do not make applications less than 7 days apart. Do not make more than 2 applications per season. Follow all pollinator safety guidelines for applications made during bloom.
  • zeta-cypermethrin (Mustang) at 0.028 to 0.05 lb ai/A. PHI 3 days for cutting or grazing, 7 days for harvest. REI 12 hr. Do not reapply at less than 7-day intervals or exceed 0.1 lb ai/A per cutting or 0.3 lb ai/A per season. Do not apply on ground within 25 ft of aquatic habitat, 150 ft if applied by air, or 450 ft if applied from ULV.