How Can I Control Aphids?

Do you want to control aphids using the biological control method?

Do you want to control aphids using low-risk (organic) insecticides?

Do you want to control aphids using synthetic insecticides?

Do you want to use residual, foliar sprays?

Among the most important natural enemies are various species of parasitic wasps that lay their eggs inside aphids. Many predators also feed on aphids. The most well known are lady beetle adults and larvae, lacewing larvae, soldier beetles, and syrphid fly larvae. Naturally occurring predators work best, especially in garden and landscape situations, but some are commercially available.

Insecticidal soaps and oils are the best choices for most situations. Oils may include petroleum-based horticultural oils or plant-derived oils such as neem or canola oil. These products kill primarily by smothering the aphid, so thorough coverage of infested foliage is required. Apply these materials with a high volume of water, usually a 1 to 2% oil solution in water, and target the underside of leaves as well as the top. Soaps, neem oil, and horticultural oil kill only aphids present on the day they are sprayed, so applications may need to be repeated.

Foliar-applied formulations of malathion, permethrin, and acephate can be used to control aphids in the landscape (nonfood crops only). While these materials may kill higher numbers of aphids than soaps and oils, their use should be limited, because they also kill the natural enemies that provide long-term control of aphids and other pests, and they are associated with bee kills and environmental problems. Repeated applications of these materials may also result in resistance to the material.

Systemic insecticides, including imidacloprid, are very effective and are especially useful for serious infestations of aphids such as the woolly hackberry aphid, which is often not effectively controlled by biological control or less toxic insecticides. Imidacloprid can have negative impacts on predators, parasitoids, and pollinators, so its use should be avoided where soaps and oils will provide adequate control. To protect pollinators, don't apply imidacloprid or other systemic insecticides to plants in bloom or before bloom.

Before planting vegetables, check surrounding areas for sources of aphids and remove these sources. Where aphid populations are localized on a few curled leaves or new shoots, the best control may be to prune out these areas and dispose of them. High levels of nitrogen fertilizer favor aphid reproduction, so never use more nitrogen than necessary. Because many vegetables are susceptible to serious aphid damage primarily during the seedling stage, reduce losses by growing seedlings under protective covers in the garden, in a greenhouse, or inside.