Sticky drippy aphid goo covers the plants under my ash trees. Aphids insert their sucking mouthparts into a leaf and draw the sap out to feed as if they’re sucking through a straw. They pull out so much ‘juice’ from a plant, they can’t absorb it all. The excess is ejected out two pipes on their hind ends called cornicles. With the large populations of aphids this year, you can feel the honeydew raining down if you stand under an infested tree. Ants climbing trees and shrubs are another good indicator of the presence of aphids. They ‘herd’ the aphids, harvesting the honeydew.
This is probably one of the worst years for aphids on ash trees I’ve seen here in Washoe Valley. The leaves have only recently begun to uncurl and grow again, an indication aphid populations, which cause the leaves to curl up in the first place, are on the decline. I’ve watched gratefully as finches, grosbeaks and other birds munch to their hearts content on aphids. The more aphids they eat, the better my trees look.
Good moisture in the spring with mild winter and spring temperatures allowed lush early growth on trees. New growth is succulent with nitrogen, which entices aphids to feed. And feed they do! Besides these voracious sucking pests on the ash trees, I had aphids on iris this year, something I’ve rarely seen. Unfortunately, roses are always prone to aphids.
When the weather is warm, aphids give birth to live young without mating, rather than laying eggs. These young produce more live young, often as many as 12 a day, in one to two weeks, so there are several generations a season. In the fall, they switch to laying eggs.
To manage aphids, lightweight horticulture oils are available for summer applications. Another management technique is to reduce the amount of nitrogen you apply or switch to slow-release nitrogen fertilizers. Aphids thrive in a high nitrogen environment.
For lettuce and row crops, protective covers work well, particularly for seedlings. Aluminum foil mulches repel aphids in young plants but may also repel aphid predator insects, such as lady beetle larvae. Hosing plants off with a strong spray of water often works. Insecticidal soap sprays are another option. Squashing by hand or pruning out aphid-infested plant parts are also alternatives. Chemical insecticides are rarely needed for aphid control. Think of them as a last resort.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at firstname.lastname@example.org.