Now is the time to begin watching for the tell-tale orangish discoloration of turfgrass characteristic of feeding damage by the greenbug aphid. A small amount of damage has been observed here in Ames.
Greenbug aphid feeds only on plants of the grass family (corn, sorghum, Kentucky bluegrass, etc.) and is not the same species as aphids that may be on trees or shrubs. Greenbugs live on the grass blades and feed on sap from the plant. As they feed they inject a toxin that causes an orange to tannish orange discoloration. Feeding damage is most severe and damage is usually first noticed in the shade beneath trees or shrubs and next to buildings. Damage in full sun is possible, however.
It is necessary to make a close inspection to determine greenbug infestations. Look closely at living blades of grass pulled from the outer edge of the discolored area. The aphids are light green and tiny but clearly visible to the naked eye [OK; so I need my reading glasses to see them clearly. These things happen with age.] Up to 40 aphids per grass blade is common.
Vigorous, healthy turfgrass is better able to withstand aphid feeding than is stunted, stressed or unfertilized turf. Therefore, a decision to spray is not based solely on the presence of aphids. Look also at the overall condition of the grass, amount of discoloration and maintenance practices (such as summer-long irrigation) to determine if spraying is justified. If orange discoloration is prominent this early in the season I would suggest treating.
Several insecticides are available for spraying greenbugs. I suggest homeowners use insecticidal soap. This treatment is not toxic to people, pets and wildlife, and preserves lady beetles and other predators that may be in the area. Apply commercial insecticidal soaps according to label directions or substitute liquid dishwashing detergents by mixing 5 tablespoons of detergent per gallon of water. Soap sprays must be thoroughly applied to be effective. Spot treat only the infested area and a small buffer beyond. A second application 10 days later will be required for best results. Two spray applications are also recommended when using traditional insecticides such as malathion, Orthene or Dursban.
This article originally appeared in the June 24, 1994 issue, p. 97.