By Tom A. Royer, Extension Entomologist
Heath Sanders, OSU southwest area agronomist, reports of some wheat fields infested with bird cherry-oat aphids. I have seen low levels of greenbugs in some of our demonstration plots as well. The decision to control aphids is especially important right now so a producer can decide to add an insecticide with their top-dress fertilizer. Greenbug infestations results in visible injury to the plants, but bird cherry-oat aphid infestations do not produce visible damage and may go unnoticed.
My suggestion is to scout the field beforehand to determine if there are GROWING numbers of either aphid that could be of concern. While scouting, keep track of Lysiphlebus mummies. Glance n’ Go accounts for aphid parasitism from Lysiphlebus wasps. If 5-10% of bird-cherry oat aphids are mummies, more than 90% of the rest are also parasitized, and control is probably not warranted.
If greenbugs are present, use Glance n’ Go to scout. At current prices of $3.00 or $4.00 per bushel, and control costs of $4.00 to $10.00 per acre, you should select the spring Glance n’ Go forms on this link: http://entoplp.okstate.edu/gbweb/spring%20glance%20n%20go3.htm using the following guidelines:
If aphids are mostly bird cherry-oat aphids, count the number of aphids on each of 25 randomly selected tillers across a zigzag transect of the field and note mummy activity. Unpublished research provided by Dr. Kris Giles (OSU) and Dr. Norm Elliott (USDA-ARS) combined with studies on spring wheat from the Dakotas and Minnesota indicate that 20-40 BCOA per tiller causes 5-9% yield loss before wheat reaches the boot stage. My suggestions: if BCOA numbers average 10-20 per tiller, figure on a 5% loss, if 20-40 per tiller, figure a 7% loss, and if BCOA aphids are more than 40 per tiller, figure a 9% loss.
Here is a Table of Preventable Loss estimates for bird cherry-oat aphids for expected yields of 30 to 50 bushels per acre, expected wheat prices of $3.00, $3.50, and $4.00 per bushel, and bird cherry-oat aphid numbers of 10-20, 20 to 40, and over 40 per tiller.
Check CR-7194, “Management of Insect and Mite Pests in Small Grains” for registered insecticides, application rates, and grazing/harvest waiting periods. It can be obtained from any Oklahoma County Extension Office, or found at the OSU Extra Website at http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2601/CR-7194web2008.pdf