Source: Oklahoma State University
Oklahoma's extended cold winter weather coupled with dry conditions prior to recent rains means wheat producers should be checking their fields for rising greenbug pressure.
Fortunately, research entomologists with Oklahoma State University's Division of Agricultural Sciences and Natural Resources worked with peers at the U.S. Department of Agriculture to develop a simple sampling methods for greenbugs called Glance 'n Go.
"Just get on the Internet, go to http://www.entoplp.okstate.edu/gbweb/index.htm and call up the Greenbug Management Decision Support Tool," said Tom Royer, OSU Cooperative Extension integrated pest management coordinator.
By selecting the Greenbug Calculator and answering a few simple questions, a grower can compute an economic threshold for controlling greenbugs. The threshold is based on the estimated cost of treating the field and the estimated price of wheat.
"Once a threshold is determined, the producer can print a scouting form, take it to a field and record the sampling results," Royer said. "The form will help the grower to decide whether or not a field needs to be treated for greenbugs."
Royer said there are several features that make Glance 'n Go a good way to make such a decision. First, the producer only has to glance at a tiller to see if it has greenbugs rather than counting greenbug numbers.
"There is no set number of samples, so growers can make a decision to treat on the go because they can stop once a decision is reached," he said. "In addition, growers can account for the activity of the greenbug's most important natural enemy, Lysiphlebus testaceipas, a tiny parasitic wasp that attacks cereal aphids."
The wasp is so effective that OSU and USDA entomologists incorporated their activity in the Glance 'n Go sampling forms.
When scouting with the Glance 'n Go system, keep a running count of tiller that have aphid mummies, as well as a running count of tillers that are infested with one or more greenbugs. After each set of five stops, the form directs the user to look at the total number of infested tillers and tillers with mummies. If there is enough mummy activity, the user will be directed to stop sampling.
"Stop but don't treat, even if you have exceeded the treatment threshold for greenbugs," Royer said. "At that level of parasitism, almost all the healthy looking greenbugs have effectively been sentenced to death and will be ghosts within five days. Save the cost of an unnecessary insecticide application."
Royer said treatment thresholds should probably fall around three greenbugs to five greenbugs per stem. Wheat growers should take care to use the January-to-May Spring form and not the September-to-December Fall form.
If a field needs to be treated, check OSU Current Report CR-7194, "Management of Insect and Mite Pests in Small Grains," for recommendations. The report is available at http://osufacts.okstate.edu.