MANHATTAN, Kan. - If dry conditions persist into early spring, it may be good for something growing in Kansas wheat fields - but it's not the wheat, a Kansas State University scientist said.

"Dry, relatively mild, early spring weather seems to favor greenbug reproduction, and the dry conditions do not favor the growing wheat," said K-State Research and Extension entomologist Jeff Whitworth.



"Thus, as the wheat breaks its winter dormancy, but lacks moisture for growth, the greenbug populations are increasing, adding additional stress to the struggling plants."

Greenbugs are aphids, Whitworth explained, which means they are relatively small, soft-bodied insects with sucking mouthparts. Greenbugs can frequently be found infesting wheat and other small grains throughout Kansas. These infestations occasionally reach damaging levels in mid fall after the first frost, but before the onset of colder winter weather if the weather stays mild and dry during this time. Sometimes, damaging levels are also seen in late winter to early spring (late February to jointing).

Greenbugs are generally not able to survive winters in Kansas, but probably do occasionally. They have no dormant stage, so either the weather needs to be fairly mild or they were lucky enough to find a protected site for overwinter survival, Whitworth said. Generally, if they do survive Kansas winters, it is in the southern counties.

Initial indications of greenbug feeding may be small reddish or purple spots on the leaves. If feeding continues, the leaves may turn yellow and die. If this continues long enough, the entire plant may be killed, he said.

"We really haven't seen this problem in Kansas for several years; however reports from Texas and Oklahoma in the last few weeks indicate a substantial greenbug problem which may lead to some northern migration into Kansas over the next few weeks," Whitworth said. "Currently, there are a few greenbugs in wheat fields sampled in southeast and south central Kansas, but populations are below the treatment threshold. Also, there are some Bird Cherry-Oat aphids in these fields."

Greenbugs are green with a dark stripe down the middle of their back, while Bird Cherry-Oat aphids are a dark olive green usually with an orange spot on the back of their body. Beneficial insects such as lady beetles and parasitic wasps often help keep these aphid populations below damaging levels, but these insects are usually not present in sufficient numbers in early spring to provide the needed control, the entomologist said.

So, with dry weather and a lack of beneficial insects to counter a greenbug infestation, aphid populations can sometimes rapidly increase, adding additional stress to already-struggling wheat.

"Now is a great time to scout your wheat fields for greenbugs, Bird Cherry-Oat aphids and any other pests or problems common to early spring wheat, such as winter grain mites and army cutworms," Whitworth said.

For information about economic injury levels, treatment thresholds and insecticide guidelines, wheat growers can check the 2006 Wheat Insect Management Guides available at K-State Research and Extension district and county offices.



SOURCE: K-State Research and Extension news release.