Russian wheat vampire might be a better name for the Russian wheat aphid (RWA). This voracious pest sucks the lifeblood out of wheat and, with it, a farmer's profits. RWA first flew into the state in 1986. Since then, it has guzzled up more than $126 million in crop losses and spraying costs for Colorado's 14,000 wheat farmers.
Insecticides can hold this scourge at bay, but they aren't a permanent solution. Besides cost and environmental concerns, insects can develop resistance to chemicals used repeatedly.
Frank Peairs, professor of bioagricultural sciences and pest management, has spent the past 12 years looking for ways to control RWA. He and his colleagues are working on four separate but related avenues of attack.
One avenue, led by Peairs, has focused on cultural practices used for wheat production. RWA can live on certain weeds when wheat isn't available, so weed control can help reduce RWA numbers. In southeast Colorado, allowing cattle to graze on early stages of winter wheat can delay spring infestations. Proper fertilization can help wheat both resist and recover from RWA feeding. Plant spacing can help reduce the number of aphids in a field. Finally, adjusting planting dates can lessen spring or fall infestations in some locations. In barley, even something as seemingly insignificant as whether irrigation furrows run east to west or north to south can have an impact on the level of infestation.
RWA-resistant wheat varieties are a second approach. Jim Quick and Scott Haley, professors of soil and crop sciences, led this effort. Their efforts led to Halt, the first RWA-resistant, commercial variety of winter wheat in the nation. Halt was released to Colorado wheat growers in 1994. Unfortunately, Halt is suited only to certain parts of Colorado. Three more RWA-resistant varieties have been released since Halt came out in 1994 and a fourth should be available within two years. More varieties give growers more options to meet local growing conditions and market needs and still get the benefits of RWA resistance.
Unfortunately, the resistance in all these varieties is based on the same single gene. "Sooner or later, RWA will figure out how to get by that resistant gene," says Peairs.
This has led to the third aspect of the RWA effort. "One way to prevent RWA from overcoming resistance is to get two genes for resistance in the same plant,"says Peairs. "It presents a more challenging puzzle for the aphid to figure out." Nora Lapitan, professor of soil and crop sciences; Dennis Knudson, professor of bioagricultural sciences and pest management; and others are working to identify additional genes for RWA resistance in winter wheat. So far, they have identified seven genes that show RWA resistance.
The fourth part of the RWA project is an integrated dryland agroecosystem approach. Led by Gary Peterson and Dwayne Westfall, professors of soil and crop sciences, as well as Peairs, this approach looks at the overall production system on dryland farms. For example, a wheat-fallow rotation is the traditional way to raise dryland winter wheat. The researchers are testing a wheat-corn-millet-sunflower-fallow rotation. Four years out of this five-year cycle are devoted to plants RWA can't eat. The aphids either move on or die of starvation. This more intensive cropping system adds to farmers' overall profitability. It also provides an environment where natural predators can thrive and prey on RWA and other crop pests, which further reduces a farmer's dependence on chemicals. This overall system can incorporate one or more of the cultural practices identified by earlier research.
None of these tools, by itself, is the single stake a farmer can drive through the heart of this vampire of a pest. But used in various combinations, they can minimize infestations at little cost to farmers or the environment.