1. Insect
  2. Legume, Grass, and Field Seed Crops
  3. Grass Seed Pests

Grass seed-Grass mealybug

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Phenacoccus graminum (western OR) and other species east of the Cascade Mountains

Pest description and damage Mealybugs are scale insects about the size of aphids, covered with waxy whitish, yellowish secretions. They feed with piercing, sucking mouthparts. Heavy populations stunt and yellow grasses. In the Palouse, nymphs of the mealybug species on Kentucky bluegrass transmit Fusarium poae at the time of head emergence. The adults feed at the node below the head. Damage in the 30 to 50% range is common in susceptible varieties. The heads become silver before the field ripens. Plants may be stunted and leaf sheaths may yellow or turn brown. In western Oregon, Phenacoccus graminum occasionally infests perennial ryegrass. Symptoms and overall damage have not been determined for this species on grass seed crops at this time.

Biology and life history Life histories of these two species have not been completely studied on their grass hosts. Adult females are present in late May through June on the Palouse.

Management-chemical control

  • bifenthrin (Brigade2EC 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.
  • lambda-cyhalothrin (Warrior II) 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 or 0.2 lb ai of chlorantraniliprole per acre per year.
  • zeta-cypermethrin (Mustang MAX) at 0.0175 to 0.025 lb ai/A. PHI 0 days forage, hay; 7 days straw and seed screenings. REI 24 hr. For forage and hay use no more than 0.10 lb ai/A per season; make subsequent applications no closer than 7 days. For straw and seed screenings use no more than 0.125 lb ai/A per season; make subsequent applications no closer than 17 days. In the Palouse, time applications to head emergence and anthesis.