With July 2008 Chicago Board of Trade wheat futures above $6 per bushel and calf prices looking good, producers need to do all they can to protect their winter cereal and pasture crops.
Greenbugs are a species of aphid that can reproduce rapidly when the temperature is above 55°F. The average temperature must stay below 20°F for a week to get a 99 percent kill. The insects reduce yields by sucking plant juices from the leaves and killing them or potentially transmitting diseases.
Oklahoma State University's Greenbug Management Decision Support Tool is an excellent decision-making resource for greenbug infestations in cereal grains. The Greenbug Management Decision Support Tool is a combination of the Greenbug Calculator and the Glance 'N Go scouting system. The Greenbug Calculator provides an economic threshold based on potential yield loss caused by greenbugs, control cost and the value of the crop. The Glance 'N Go system provides the scouting instructions and mechanism to determine whether the economic threshold has been exceeded and whether or not to apply chemical treatments. The recommendation to spray or not is based on the time of year, the stage of crop growth, the cost of treatment, the value of the grain crop, the level of infestation and the influence of beneficial insects. The tool does not currently provide a recommendation for graze-out systems.
- Step 1: Count the average number of tillers per plant and leaves per tiller. Tillers are additional branches or shoots originating at the basal node of a grass plant.
- Step 2: Access the Greenbug Calculator. Input the number of tillers, number of leaves per tiller, treatment cost and grain value to get the correct scouting worksheet (Glance 'N Go) for the economic threshold.
- Step 3: Start at a random location in the field and check three tillers for greenbug infestation, and mark results on the correct scouting worksheet. As you check each tiller, also note when "mummies" - greenbugs that are swollen and usually a tan color - are present. A parasitic wasp has deposited an egg in these greenbugs, and the wasp larvae will use them for food during development. Parasitic wasps can cause a greenbug population to crash in a short period of time, eliminating the need for chemical control.
To use this resource,
There is a link to an insecticide selector providing several options for chemical control of greenbugs, or you can contact your Noble Research Institute soil and crops specialist for recommendations. Contact your chemical dealer for the price of these options including application.
After counting the three tillers at the first location, walk at least 15 steps to the next location and repeat the process until five separate sites have been checked. Mark the number of tillers with greenbugs and with mummies, total the numbers, and read the recommendation on the Glance 'N Go worksheet. The recommendations are "don't treat," "keep sampling" or "treat."
Repeat this step until a clear recommendation is made or until 90 tillers have been checked. If no clear recommendation is made after checking 90 tillers, repeat the procedure in two to six days. This happens when the greenbug population is so close to the economic threshold that a decision cannot be made until the population has time to develop or crash.
If you do not have Internet access, determine the crop stage, cost of treatment and grain value as indicated above, then scout and record the tillers with greenbugs and mummies for three tillers at 30 different locations. Call a Noble Research Institute soil and crops specialist at 580.224.6500 with these results, and they can recommend if treatment is justified.
Integrated Pest Management tools such as OSU's Greenbug Management Decision Support Tool have the potential to reduce pesticide usage, decrease impact on the environment and increase your bottom line.
Photos, courtesy of Dr. Tom Royer, Dept. of Entomology and Plant Pathology, Oklahoma State University