The greenbug, Schizaphis graminum, a long-time pest of small grains and sorghum, has become a pest of Kentucky bluegrass turf in several midwestern states. While the greenbug is common throughout the Northern Great Plains, it has only rarely been a significant pest in turfgrasses.
Description and Life History
The greenbug is a light green aphid, about 1/10 inch long. It has a narrow, dark green stripe down the back and black-tipped legs, antennae and cornicles ("tail pipes"). There are both winged and wingless forms. Greenbugs migrate to the Northern Great Plains from southern regions each year from April through June. Eggs hatch within the female aphid which then gives birth to live young. A single female can produce 1 to 8 offspring each day for 2 to 3 weeks. Young aphids reach maturity in 6 to 10 days and begin to reproduce without mating. Depending on environmental conditions, from 12 to 20 generations can occur each season.
Symptoms of Damage
Greenbugs feed by removing juices from plant tissues with piercing/sucking mouthparts. As they feed, greenbugs inject a potent salivary toxin which kills plant cells and causes discoloration of the leaf blades. Heavily infested plants turn yellow and may eventually die. Circular patches of yellow to light-orange or dying turf may be an indication of greenbug infestation. If greenbugs are the problem, close examination of leaf blades should reveal colonies of feeding aphids. An infested grass blade may support 30 or more aphids. Concentrations of more than 3,000 greenbugs per square foot have been recorded. Mild spring and summer weather facilitates greenbug survival and may result in damaging outbreaks. Infestations generally arise in shaded sites such as under trees or in the shadow of buildings, but may occur in sunny areas as well.
Greenbugs can be detected by carefully inspecting the grass blades for the presence of greenbug colonies or by sampling the turf with an insect sweeping net. The presence of lady beetles, lacewings, parasitic wasps and other natural enemies that feed on aphids may also indicate a greenbug infestation.
There are no established treatment threshold levels for greenbugs on turfgrass. However, if large numbers of greenbugs are present, and injury is increasing, an insecticide application may be warranted unless natural enemies are abundant. Apply a liquid insecticide to the greenbug infestation, including a 2 to 3 foot border around the damaged area. Thorough coverage is important. Do not irrigate for at least 24 hours after treatment.