The salivary toxins injected by RWA during feeding damages plant chloroplasts, resulting in reduced photosynthetic ability, delayed leaf initiation and tillering, reduced numbers of fertile tillers, shoot and root biomass, grains per ear and grain weight. Yield impacts are determined by the percentage of infested tillers and plants and crop development stage. Heavy infestations during early growth can cause serious damage (under USA conditions). From early booting to soft dough stage, feeding on upper leaves, in the leaf sheath and next to the developing head, can cause direct yield losses. In wheat and barley, damaged leaf tissue does not recover. If aphids are controlled, new growth proceeds normally (new root and shoots are unaffected) and plants may recover unless excessively stressed. After soft dough stage, further impact is minimal.
See chemical control for economic thresholds (ET).