Bird cherry-oat aphids and greenbugs on wheat
Greenbugs are pale green aphids with a dark green line down the back and antennae as long as the body. Greenbugs usually prefer to feed on the underside of lower leaves. Damage can occur in fall or spring, with tiny reddish spots on leaves signaling a beginning infestation. Later, infested leaves turn yellow, then reddish brown and eventually die. In the field, damage often appears as yellow or reddish-brown irregularly shaped patches that can spread to become almost field-wide.
The guidelines below are useful in estimating the need for greenbug control. For convenience, damaging levels are expressed as the number of greenbugs per foot of row, but in assessing the need for control, the thickness of the stand also becomes important. 50 greenbugs per foot of row in a thin stand would be more serious than in a thick stand because the number of aphids per plant would be greater. Similarly, larger plants can tolerate somewhat larger numbers of greenbugs before significant damage occurs.
Approximate Damaging Levels of Greenbugs
Stage and development of plants No. of greenbugs per linear foot
Seedlings, thin stands less than 3 tillers 50
3- to 6-inch wheat, 3 tillers or more 100 to 300
6- to 10-inch wheat 300 to 500
Overwintering greenbugs can rapidly develop into damaging infestations during warm periods in February and March, and close surveillance of fields is necessary if greenbugs are present. Beneficial insects such as parasitic wasps and ladybeetles become increasingly effective in reducing greenbug populations around mid-April. Once parasitism levels reach between 10 and 15 percent, greenbug populations usually decline fairly rapidly.
Greenbug control on small grains is occasionally needed during periods of relatively cool weather (below 60°F, but above freezing). Experience has shown that good results are possible under these conditions with some, and perhaps most, of the recommended insecticides. Dimethoate may be an exception, however. It may not give acceptable control below 60°F.
Oklahoma State University has developed a sampling program called “Glance ‘n’ Go,” which calculates a greenbug threshold based on the cost of control, the market value of wheat and the month of the year. For more information on their greenbug pest management decision support system, see the web site at: http://entoplp.okstate.edu/gbweb/.
Consider avoiding pesticide applications when beneficial insects such as lady beetles and parasitic wasps are active, as these are often abundant enough to prevent greenbugs from reaching damaging levels. Augmenting greenbug predators such as ladybeetles or lacewings by importing and releasing is not advisable.
For more detailed information on bird cherry-oat aphids and greenbugs, see:
For specific treatment options, see K-State publication “Wheat Insect Management 2013” MF-745 at: www.ksre.ksu.edu/bookstore/pubs/mf745.pdf