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

Alfalfa seed-Spider mite

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Includes

Pacific spider mite (Tetranychus pacificus)
Strawberry spider mite (T. turkesani)
Twospotted spider mite (T. urticae)

Pest description and crop damage Not insects, mites are eight-legged animals less than 0.03 inch long. Mites pierce the epidermis of the leaf's underside and suck juices, causing yellowing, bronzing, and even leaf death. Canopies of silk covering plants accompany large populations of twospotted mite, and serious plant injury and yield loss result. (Chemical controls should be applied much earlier to prevent this damage.)

Sampling and thresholds Late-season infestations may not affect seed production seriously (after seed has been set and harvest is less than 2 weeks away). Treatment may be justified when 25% of leaves show damage in early summer, 50% in midsummer. Treatment actually may not be justified with 75 to 100% leaf damage after August 15, as seed usually has been set and fields are drying before harvest.

Management-chemical control

  • abamectin (Agri-Mek, ABBA 0.15EC) at 0.01 to 0.02 lb ai/A via ground application; 0.014 to 0.02 lb ai/A via air application. PHI 12 hours. Do not retreat within 21 days. Do not exceed two applications or 0.04 lb ai/A per season. No part of crop may be used as feed. Do not apply at ground level within 25 ft of aquatic habitat, 150 ft if applied by air. SLN ID-98007; OR-040013; WA-980019.
  • bifenazate (Acramite 4 SC) at 0.5 to 0.75 lb ai/A. PHI 14 days. REI 12 hr. Make only one application per year. SLN OR- 080031; WA 070008; ID-070006; NV-070003; UT-070003; WY-070004.
  • etoxazole (Zeal) at 0.035 to0.525 lb ai/A. Do not apply more than 3 oz Zeal per acre per season or make more than one application per season. Apply by ground in a minimum of 20 gal per acre or by air at 10 gal per acre. Coverage is essential for good control. Use of higher water volume will assure better coverage. Best results are achieved when mite populations are low. Zeal is predominately an ovicide/larvicide and should be used early in the life cycle of mites.
  • hexythiazox (Onager) at 0.09 to 0.13 lb ai/A. PHI 28 days. REI 12 hr. One application per season. Do not graze or cut crop for hay or forage. Effective on immature motile mite stages.
  • propargite (Comite) at 1.23 to 2.05 lb ai/A. REI 7 days. Do not feed. Do not exceed 1.6 lb ai/A in ground application. Ground application with 25 to 40 gal/A water gives best results. Use at least 10 gal/A water if applying by air. Do not apply in mixtures with insecticides; this increases hazard to pollinating bees. After the first 48 hours of the REI, workers may enter the treated area to perform hand labor if they wear the early-entry personal protective equipment. SLN ID-960016; OR-030020; WA-040019.
  • Sulfur DF at 2.4 to 4 lb ai/A. PHI 0 days. REI 24 hr. Repeat every 14 days as necessary.