Chemical and organic control of aphids

Continue to look for aphid infestations during the growing season. Not only do aphids harm plants directly, they are also the main carriers of plant diseases.

When possible, tolerate small aphid populations. Insecticides should be used only as a last resort. Before application, ensure plants are receiving the appropriate cultural care and take steps to protect natural predators. 

Organic sprays like natural pyrethrum, plant oils (neem, canola, etc), and insecticidal soap can be used in spring and summer. These products have a short persistence so may need to be applied a number of times before the aphid population is under control. Apply insecticidal soap before the sun rises or at dusk, spraying the plant thoroughly, especially at the undersides of the leaves. Do not spray in hot weather.  Plant oils and fatty acid products are less likely to affect larger, benefical insects like ladybirds and lacewings.

Contact (spray) insecticides, particularly synthetic pyrethroids such as lambda-cyhalothrin, deltamethrin, and cypermethrin, are used to control aphids. Systemic insecticides containing Flupyradifurone are available for outdoor and glasshouse use. Acetamiprid, a systemic neonicotinoid insecticide, is also available for aphid control. 

Follow instructions carefully when using insecticides. Plants in flower should not be sprayed due to the danger insecticides pose to bees and other pollinating insects. Insecticides can cause an outbreak of red spider mite since they often kill benefical insects that control mites.