Herbicide and Nonherbicide Injury Symptoms on Spring Wheat and Barley

Aphids
Aphid populations exceeding 30 percent of stems infested can cause serious yield reductions. Although aphids can appear at different times during the growing season, they cause the most damage if they reach high numbers between tillering and the flag leaf stage. Three aphid species that are the most common in the north central small grain production area are the English grain aphid, Macrosiphum avenae (Fab.); the birdcherry oat aphid, Rhopalosiphum padi (L.); and the greenbug, Schizaphis graminum (Rond.). Aphids have piercing-sucking mouthparts that draw plant sap from leaves when feeding. Feeding injuries from high aphid populations result in slow plant growth, stunted plants, and chlorotic leaves. In addition to feeding injuries, these aphid species are capable of transmitting plant diseases such as barley yellow dwarf virus. Crop injury caused by aphids is similar in appearance to the chlorosis and stunting injury symptoms caused by herbicides belonging to the aryloxyphenoxypropionate and benzonitrile families and propanil (Stampede). See photo 36.

Photo 36 Leaf yellowing shown here is the result of aphids injecting their toxic saliva while feeding on leaves.

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