The relationship of selected herbivores and herbivore complexes to the incidence of winter and summer annual weeds associated with alfalfa was evaluated over a 3-yr period. Winter annual weed populations in the first cutting, second production year, were associated with aphid stress imposed during the previous fall and exacerbated by a severe infestation 6–8 wk before harvest. A significant (P<0.05) interaction between Egyptian alfalfa weevil and aphids affected winter annual weed percentages in the first harvest of the third production year. Summer annual grass populations did not develop until the third year. Egyptian alfalfa weevil had a significant effect on grass percentages in three of the four cuttings in which grasses were present.