The grass beneath one of my trees has turned brownish orange. Why?

FAQ
Question: 

The grass beneath one of my trees has turned brownish orange. Why?

Answer: 

Greenbug aphids may be responsible for the brownish orange color of the turfgrass.  Greenbug aphids feed only on plants of the grass family (Kentucky bluegrass, corn, sorghum, etc.).  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 brownish orange discoloration.  Feeding damage is most severe and damage is usually first noticed in the shade beneath trees or shrubs and next to buildings. 

Greenbug aphids are quite small, but can be seen with the naked eye.  The aphids are typically found on blades of grass pulled from the outer edge of the discolored area.  The aphids are light green in color.  Forty or more aphids can be found on a single blade of grass. 

Vigorous, healthy turfgrass is able to withstand some greenbug aphid feeding.  Treatment may be necessary if the grass is stressed because of poor growing conditions or the brownish orange discoloration is extensive.  Greenbug aphids can be controlled with insecticidal soap or chemical insecticides.  Spot treat only the infested area and a small buffer beyond.