Could bird cherry-oat aphids be a problem on wheat this spring?
Bird cherry-oat aphids (Fig. 1) have been reported in large numbers this month in several Oklahoma fields by Tom Royer, Extension Entomologist with Oklahoma State University. The very strong south winds observed last few days increase the risk that aphids might migrate into Kansas in large numbers. Thus far, bird cherry oat aphids have been reported in small numbers in the central corridor of the state, but this is a situation producers should be aware of especially following the freeze events observed last few days (see Agronomy eUpdate special issue 556 of March 21st, 2016, “Potential for injury to wheat in Kansas from below-freezing temperatures” for more information).
The only years that we have seen bird cherry-oat aphid feeding on wheat that caused concern just due to the numbers of aphids were years in which freeze damage played a part in stressing the wheat, killing some tillers, and thus concentrating the aphid populations on the reduced number of wheat plants and tillers that survived the spring freeze. Otherwise, lady beetles/lacewings/parasitic wasps are usually effective at regulating aphid populations.
Bird cherry-oat aphids are usually the first aphids to infest wheat in the spring and the last to still infest wheat in the fall. Wheat growing under good conditions can withstand more aphid feeding than wheat under stressful growing conditions. If there are 20-50 aphids/tiller and very few beneficials (lady beetles/lacewings/parasitic wasps) then an insecticide application may be justified, especially between boot and heading. Otherwise, the beneficials usually keep aphids under control. An insecticide application will decimate beneficials.
Another factor to consider is that an abrupt shift to cold temperatures after a warm spell in spring is usually beneficial to aphids as compared to their biological control agents. It is especially important to scout for aphids under these circumstances because aphids can sustain economic injury to wheat when in abundant numbers. The economic damage caused by aphids can be furthered if the primary tillers of the wheat crop have been damaged by the freeze event, a situation in which a higher percentage of wheat’s yield will depend on the secondary tillers. Secondary tillers, if exposed to large numbers of aphids from the start, can be severely damaged and grain yield impaired by harvest time.
Decisions to apply pesticides to control aphids should be taken based on the number of aphids present. Producers should count the number of aphids on 25 - 50 randomly selected tillers across a zig-zag transect of the field. Previous research has shown as much as 9% yield loss when 20-40 bird cherry-oat aphids per tiller were present before boot stage.
Figure 1. Bird cherry-oat aphid adult female and nymph. Photos courtesy of K-State Department of Entomology.
Romulo Lollato, Wheat and Forages Specialist
Jeff Whitworth, Extension Entomologist
Holly Schwarting, Research Associate, Entomology