Grass seed-Thrips

Anaphothrips obscurus and others

Pest description and crop damage Small, winged or wingless, narrow insects about 0.06 inch long. If winged, the insect has four wings with a characteristic "hair" fringe margin. Thrips feed by rasping the surface of the leaves with their mouthparts and sucking up the exuding plant juices. This whitens, yellows, or stipples leaves. Eggs are inserted into stems. Thrips cause "silvertop" in certain fine-leaf grasses when large numbers lay eggs in stem tissue of seed heads during and shortly after boot stage.

Biology and life history Adults overwinter in and around grass seed fields. They become active in the spring and lay eggs in host plant tissues. There are many generations per year.

Scouting and thresholds Inspect susceptible varieties as heads approach boot stage. Large numbers of thrips (25 per head) probably result in silvertop symptoms in fine-leaf grasses.

Management-chemical control

  • bifenthrin (Brigade 2EC and WSB) at 0.1 lb ai/A. Apply in spring and fall when insects are present at their economic threshold level. Maximum amount allowed is 0.2 lb ai/A per season. Applications made no less than 14 days apart. PHI 30 days prior to harvest for forage, hay and seed.
  • carbaryl (Carbaryl, Sevin) at 1 to 1.5 lb ai/A. PHI 14 days. REI 12 hr. Up to two applications per year but not less than 14 days apart. Do not exceed 3 lb ai/A per season. Use high pressure to improve spray penetration into boot.
  • cyfluthrin (Baythroid XL) at 0.02 to 0.022 lb ai/A. PHI 0 days. REI 12 hr. Maximum amount allowed per 5 day interval is 0.022 lb ai/A. Maximum amount allowed per crop season is 0.089 lb ai/A.
  • dimethoate at 0.25 to 0.33 lb ai/A. PHI 14 days. Do not graze or feed hay, forage, seed, or use screenings from treated fields. Seed conditioners must be informed if seed is from a treated field.
  • lambda-cyhalothrin (Warrior) at 0.02 to 0.03 lb ai/A. PHI 0 days for grazing and cut for forage, 7 days for straw and seed crop. REI 24 hr.
  • lambda-cyhalothrin/chlorantraniliprole (Besiege) at 6.0 to 10.0 fl oz/A. PHI 0 days for grazing and cut for forage, 7 days for straw and seed crop. REI 24 hr. Do not exceed a total of 27.0 fl oz of Besiege or 0.09 lb ai of lambda-cyhalothrin-containing products or 0.2 lb ai of chlorantraniliprole-containing products per acre per year.