The skin of the parasitized aphid turns crusty and golden brown, a form called a mummy. Many predators also feed on aphids. Naturally occurring predators work best, especially in a small backyard situation. Commercially available lady beetles may give some temporary control when properly handled, although most of them will disperse away from your yard within a few days. Whole colonies of aphids can be killed by these pathogens when conditions are right.
Weather can also impact aphids.
Populations of many species are reduced by summer heat in the Central Valley and desert areas, and aphid activity is also limited during the coldest part of the year. However, some aphids may be active year round, especially in the milder, central coastal areas of California. Cultural Controls Before planting vegetables, check surrounding areas for sources of aphids and remove them. Check transplants for aphids and remove them before planting. Where aphid populations are localized on a few curled leaves or new shoots, the best control may be to prune these areas out and dispose of them.