Grass seed-Aphid

Bird cherry-oat aphid (Rhopalosiphum padi)
Corn leaf aphid (Rhopalosiphum maidis)
English grain aphid (Macrosiphum avenae)
Rose grass aphid (Metopolophium dirhodum)

Pest description and crop damage Aphids are smaller than 0.04 inch (1 mm), winged or wingless, and feed in colonies on leaves and stems of grasses. They vary in color from yellow to dark green and have two distinctive cornicles, which look like "tailpipes" on the top-side end of the abdomen.

Perennial ryegrass, fescue, orchardgrass and Kentucky bluegrass are susceptible to damage from large populations of bird-cherry oat aphid. Damage is most significant to seedling plants, particularly in direct seed or no-till fields and when aphids on the previous crop may colonize emerging seedlings as the old crop dies down. Aphids remove plant sap, secrete honeydew, and mechanically damage leaf tissue and developing seed heads. Light seed and reduced yields can occur, although not very often.

All aphid species colonizing grass (except possibly root aphid species not mentioned in this section) can vector barley yellow dwarf virus (BYDV) among susceptible grass and cereal crops. Symptoms of BYDV have been pronounced in Willamette Valley grasses in recent years. Refer to the PNW Plant Disease Control Handbook for information on the virus.

Scouting and thresholds Inspect seedling grasses for aphid colonies. Winged forms colonize fields in irregular patterns, often according to prevailing-wind direction and wind-blocking features along field margins. Aphid flights from region to region and locally from field to field occur late spring through fall. When bird-cherry oat aphids exceed an average of 10 aphids per two- to six-leaf seedling, and the population appears to be increasing in the absence of natural predators or parasites, crop may be injured even in the absence of virus.

When heads begin to form during boot stage, aphid populations averaging 10 to 20 per stem or head (and increasing) may cause damage if not checked biologically or with insecticide. Drought-like conditions, weak stands, and fields under other stresses magnify aphid damage.

Management-biological and physical controls

Aphid populations are susceptible to rainy, windy weather and sudden cold. Unseasonably high temperatures from April through June can reduce aphid populations quite effectively.

Ladybird beetles, big-eyed bugs, damsel bugs, syrphid fly larvae, and parasitic wasps may regulate aphid populations below damaging levels in grasses. Consider these beneficial when deciding whether or not to apply an insecticide. Individual aphids that are parasitized appear brown to gold. If predator insects and parasitized aphids increase from one week to the next, and there is a corresponding drop in aphids as the weather dries and warms, sprays often are unnecessary from late April through June.

Management-chemical control

  • bifenthrin (BrigadeÆ 2EC and WSB) at 0.1 lb ai/A. Apply in spring and fall when aphids are seen. 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.
  • dimethoate at 0.25 to 0.33 lb ai/A. PHI 14 days. REI 48 hr. 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. Control is best when grass is succulent and not drought stressed.
  • lambda-cyhalothrin (Warrior) at 0.02 to 0.03 lb ai/A. PHI 0 days for grazing and cut for forage, 7 days straw and seed crop. REI 24 hr.
  • lambda-cyhalothrin/chlorantraniliprole (Besiege) at 6.0 to 10.0 fl oz/Acre. 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.
  • malathion at 0.9375 to 1.25 lb ai/A. PHI 0 days. REI 12 hr. Maximum single application rate is 1.25 lb ai/A. Maximum one application of malathion allowed per year.
  • zeta-cypermethrin (Mustang MAX) at 0.014 to 0.025 lb ai/A. PHI 0 days forage, hay; 7 days straw and seed screenings. REI 12 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.