A new strain of Russian wheat aphid that is damaging previously resistant varieties of wheat has been identified in Colorado by Colorado State University Cooperative Extension agents. University experts, including Cooperative Extension agents and researchers, are asking farmers to monitor their fields and call their local Colorado State Cooperative Extension office if they see signs of infestation.
The new strain of aphid is attacking all wheat varieties this spring that were developed to be resistant to the original strain of the insect, especially in central and southern Colorado. In particular, Prairie Red is consistently infested with the new aphid biotype, known as biotype B.
Prairie Red contains the same Russian wheat aphid-resistant gene as the other resistant varieties developed by Colorado State University: Ankor, Halt, Prowers 99 and Yumar. Kansas State University’s resistant variety, Stanton, also is susceptible to infestations from the new biotype. All of these varieties continue to be resistant to the original aphid, known as biotype A.
Colorado State University experts are investigating the aphid outbreak and working to determine sources of resistance that can be used in future varieties, predict next year’s infestation risk, the origin of the new biotype and the distribution of the new and old biotypes. Those experts include Jerry Johnson, Cooperative Extension specialist; Scott Haley, Department of Soil and Crop Sciences wheat breeder; Frank Peairs, Cooperative Extension entomologist; Ron
Meyer, Cooperative Extension agronomist; Tim Mackin, Cooperative Extension agronomist; and Thia Walker, Agricultural Experiment Station Russian wheat aphid specialist in southeastern Colorado.
Researchers can’t yet predict the distribution of the two biotypes of aphids next year. However, the varieties resistant to biotype A still should be considered by farmers for the next growing season, particularly by producers with a greater risk of Russian wheat aphid infestation. Producers are encouraged to call their local Cooperative Extension office to discuss their options.
Information to help farmers decide which varieties to consider planting next year can be found at http://www.colostate.edu/Depts/SoilCrop/extension/CropVar/wheat02/dectree02.htm and additional information can be found at http://wheat.colostate.edu. Farmers in Colorado can manage aphids with a combination of predatory insects, judicious use of insecticides, controlling weeds that host the insect and by planting resistant varieties. Information about managing Russian wheat aphids can be found at http://www.highplainsipm.org and http://www.ext.colostate.edu/pubs/insect/05568.html, or by contacting the local Colorado State Cooperative Extension office.
Researchers are not sure if the new biotype adapted in response to resistant varieties of wheat or if it was introduced from another country, where different types of the insect exist. The aphid is currently being studied by the U.S. Department of Agriculture – Agricultural Research Service in Stillwater, Okla., to determine the genetics of the aphid.
Since the original strain of Russian wheat aphid entered Colorado in 1986, it has cost the state’s 14,000 wheat farmers more than $132 million in crop losses and insecticide control efforts.
"A new biotype of the Russian wheat aphid is not a completely unexpected development, but there was no way to prepare for it because we could not forecast how the aphid would develop and what sources of resistance would be effective," said Frank Peairs, Colorado State University Cooperative Extension entomologist who, along with other experts at the university, has spent 17 years developing tactics to control the aphid.
The aphid damages wheat and other grains by injecting saliva into grain and sucking sap from plants. If left untreated, the aphid can destroy more than half of a crop. The aphids begin to appear in crops in April and May and their population peaks in July, the month most common for harvesting wheat in the state. They often survive in host plants such as wheatgrass and barley and begin to winter in wheat crops in October and November, shortly after they are planted. The aphid can survive the winter in most areas of the state where wheat and grain is grown.
In Colorado, 4.7 million acres has had to be treated with insecticides to control the aphid since it was introduced in 1986. This represents about 30 percent of the total wheat acreage in the nation treated for the aphid. Aphids prevent young wheat leaves from flattening out, or unrolling, and live within the tubes formed by tightly curled leaves. This makes it difficult to kill the aphids with predatory insects and insecticides.