Gardening Solutions: Controlling Aphids

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aphids on flowering kale

Aphids on flowering kale

Aphids are small soft-bodied insects that suck plant juices. The whitish cast skins can be mistaken for whiteflies, an entirely different problem. That’s why it’s always best if you bring in a sample in a small plastic bag for diagnosis. The honeydew (sticky sugary sap) excreted provides an excellent medium for growing black sooty mold, many gardeners frequently mistake the sooty mold as the problem, when it is actually a symptom of aphid infestation. Copious honeydew and sooty mold can create a sticky, unsightly mess on trees, sidewalks, cars, and other surfaces beneath the plant.

Adult aphids are usually 1/8 inch, pear-shaped, with long legs and antennae, and vary from green, yellow, brown or red to black. Woolly aphids are covered with a waxy, whitish to gray coating (and may be mistaken for mealybugs). Woolly apple aphids can be found on apple trees, cotoneaster, hawthorn, pyracantha, elm, ash, and some conifers.

aphidAphids also have a pair of tube-like projections (cornicles) near the hind end of the body.

SYMPTOMS – Feeding by high populations can slow plant growth or cause leaves to yellow, curl, or drop early. Some species distort stems or fruit or cause galls birth to on roots, leaves, or stems. They can also transmit viruses, not usually a problem in landscape trees and shrubs.

During warm weather, aphids may go through a complete generation in less than 2 weeks. There are many generations per year, populations can increase rapidly in moderate temperatures. Throughout most of the year, adult aphids will give live young without mating! (They can also produce over wintering eggs, that’s why we suggest using dormant sprays starting in the fall.)

MANAGEMENT-  Sprays – Predators and parasites may not always appear in sufficient numbers until after aphids become abundant. To preserve beneficials use earth-friendly products like Earth-friendly products like Bonide Insecticidal Soap or Rose Rx. Use baits (Monterey, Amdro, Terro) or sticky barriers (Tanglefoot/collars) to control honeydew-seeking ants, since they protect aphids from their natural enemies.

Mechanical Controls – Aphids can be hosed off with a strong stream of water or pinched by hand.

Biological Controls – Lady beetles (Hippodamia convergens) and their larvae, which resemble small black and orange crocodiles, the larvae of lacewings, are common predators, as well as many small wasps. The wasps lay their eggs inside the aphids, leaving “mummies” that are round and tan, with a small hole where the adult has chewed its way out.

Many aphid predators are attracted by the presence of honeydew, as well as nectar-producing plants.

2 comments on "Gardening Solutions: Controlling Aphids"

  • Jessica

    Is using sprays ok on flowering/fruiting plants to get rid of aphids or will that affect the pollinators as well? Also is apply diatomaceous earth to the topsoil an option too?

  • Sloat Garden Center

    Hi! Some sprays, even organic ones, can harm bees. It is recommended to spray in the late afternoon once bees have finished foraging for the day. Insecticidal soap or Bonide All Seasons oil are the least harmful to bees. Applying diatomaceous earth to the topsoil will hinder sow bugs, ants, earwigs, slugs, and snails, but will not bother aphids. Hope this helps!

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