Impact
Russian wheat aphids (RWA), Diuraphis noxia, are a localized problem in the San Luis Valley. Aphids are brought in from other areas by winds. RWA infestations are more frequent in the eastern and southern areas of the San Luis Valley.
Oats are resistant to RWA. Triticale is moderately resistant, but damage can still occur. Wheat is susceptible and barley is the most susceptible.
Heavy infestations may cause severe yield losses. Yields can be reduced by 50 percent. RWA does not transmit viruses.

Description and Symptoms

RWA are pale green, long, and spindle-shaped (football like) with no visible cornicles.

Antennae are short compared with other aphid species.

A projection above the tail gives Russian wheat aphids a two-tailed appearance.

Colonies of aphids are produced inside rolled small grain leaves.

RWA secrete a toxin that causes white or purple streaks on the leaves. Purple discoloration is more common in cool weather, while white streaks and leaf rolling are more prominent in warm weather.

Heads of infested plants may become twisted and distorted and may not emerge. Some heads may emerge in a fishhook shape.

Infestations can spread rapidly. As the colonies become crowded or the plant declines, wingless aphids can move to neighboring plants.

Winged forms may also disperse and infest other fields.

Integrated Management

Plant as early as possible.

Plant resistant cultivars when available.

Maintain a healthy grain crop to avoid plant stress that can cause greater aphid susceptibility.

Scout suspect fields weekly for early detection.

Estimate the economic threshold for wheat based on the following:

Percent Infested Tillers =Control Costs per Acre x 200/Expected Crop Value per Acre

Barley threshold is probably lower due to grain quality effects.

After flowering, use a factor of 500 in the numerator instead of 200.

Select contact and systemic insecticides labeled for control. Refer to Colorado Pesticide Guide.

This material is based on work supported by the San Luis Valley Water Quality Demonstration Project Best Management Practices Advisory Committee, Colorado State University Cooperative Extension, Farm Service Agency, Natural Resources Conservation Service, and the U.S. Department of Agriculture under authorization as 1991 U.S. Department of Agriculture Water Quality Demonstration Project.