The dry weather in May and June caused large, noticeable populations of several kinds of aphids, including leafcurl ash aphid, maple aphids, oak aphids, and bean aphid on euonymus. The greenbug is also on this list of current troublesome pest species.
The greenbug feeds on sap from over 60 species of plants in the grass family. Major hosts are corn, small grains and turfgrasses, including Kentucky bluegrass, annual bluegrass, fescues and perennial ryegrass.
Greenbugs live above ground on the grass blades. Although they may be present in large numbers -- 30 or more aphids per blade, amounting to several thousand aphids per square foot of turf -- greenbugs are usually detected by the damage symptoms that result from their feeding. While sucking out the plant juices from the grass blades, the aphids inject a toxin that kills a portion of the blade around the feeding site. Early damage symptoms consist of a barely detectable yellowing of the turf. Later damage takes on a characteristic orange to tannish-orange color.
Greenbug damage is usually noticed as large round discolored patches under shade trees, or in the shade along buildings or under shrubbery. However, extensive damage from large populations can occur in full sun.
Diagnosing greenbug infestations is fairly simple because of the characteristic color and pattern of the damage. For a positive diagnosis, pull individual green grass blades from the outer edge of the discolored area. The tiny aphids are light green in color and difficult to see, but if present, will be on the upper surface of the grass blade. They are visible with the naked eye, but a magnifier helps. If you find patches of greenbugs, spot-check the entire lawn for additional infestations.
Greenbugs are subject to many natural controls including predators (lady beetles, lacewings, bigeyed bugs, spiders, etc), a parasitic wasp and weather, especially rain storms. The parasite and predators can suppress greenbug outbreaks, but when weather conditions favor the aphids and work against the biological controls, severe damage can result.
Chemical control is warranted when greenbug populations cause noticeable damage by early to mid-summer and natural enemies or weather conditions are not keeping populations in check. Healthy, vigorous turf that is lightly damaged will usually recover, but weakened turf or turf severely damaged early in the season may be killed.
Liquid sprays of malathion, Orthene or insecticidal soap are generally recommended, although other broad-spectrum turf insecticides should also provide good control. Granular insecticides do not give good control. Greenbug infestations are often spotty and a 'spot' treatment that covers the infested area plus another peripheral area approximately 6 feet wide should suffice. Thoroughly cover the grass blades and do not mow or irrigate for 24 to 48 hours after application.
Carefully evaluate the condition of the grass following greenbug management. If the grass crowns are healthy, rejuvenate with a light fertilization and regular watering for the remainder of the summer. If the entire grass plant has been killed, resodding now is possible if irrigation is available, or you can try overseeding now with perennial ryegrass. Wait till fall to re- establish Kentucky bluegrass.
This article originally appeared in the July 15, 1992 issue, p. 125.
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