The toxin causes brown spots at sites where aphids feed and causes the plant to turn yellow. Plants are set back from their normal maturity date. The aphid can carry barley yellow dwarf virus and maize dwarf mosaic virus. In another instance, serious outbreaks were attributed to the coincidence of aphid flight with a time when late crops were at a succulent stage of development. Late-seeded crops are more susceptible because they are less able to withstand attack, have more attractive succulent growth, and are less likely to produce a crop should plants recover.
Damage is caused primarily by the toxin that is injected into the plant.
From a distance, however, fields took on a yellow appearance that was evident, on close inspection, in the top growth. In many barley fields, the unnatural yellow color was likely attributed to severe scald and net blotch, which were prevalent in 1986. Economic threshold From 5 to 25 aphids per stem warrants chemical control action, that is, the economic threshold is dependent on the stage of crop growth, the health of the crop and growing conditions. Abundant predators and parasites should enable greater populations to be tolerated. The species has been abundant in hot dry weather.