Almost all of the trees and shrubs that grow here in the high mountains, as well as many plants, can become infested with aphids.
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These really small (less than an eighth of an inch) insects reproduce amazingly quickly and feed on the phloem or sap of the plant leaves and twigs. They usually do not seriously damage the plants, but they certainly are a pest.
Most often, aphids cause problems by excreting a sticky, messy substance called honeydew, which attracts ants or creates a sooty-looking mold on leaves. This pest also can detract from the appearance of your plants by causing the leaves to curl as they suck out the sap for sustenance.
The life cycle of aphids is somewhat complicated. They generally lay their eggs on a primary host plant that gives protection and sustenance through the winter and then move on to a secondary host plant throughout the growing season.
The aphids we notice in the summer all are females who reproduce asexually and give birth to their young at a rate of as many as 20 per day. As winter draws near, winged males find a special type of wingless female to mate with and lay eggs on a primary host plant.
Luckily, aphids have many natural enemies, including lady beetles (ladybugs), green lacewings, syrphid flies and small parasitic wasps, all of which are abundant in Yampa Valley gardens. If many ants are attracted by the sweet honeydew produced by aphids, it may be difficult for natural enemies to reduce the population of aphids since they are repelled by the ants. Killing the ants with sprays, sticky traps or powders is one way to allow the natural enemies access to your aphids.
If that doesn’t work, aphids and the unsightly honeydew easily are removed by squirting the plant with a garden hose if you have adequate water pressure and are able to access the infested parts of the tree or shrub.
Another method of controlling aphids is by offering a host plant to them like my friend Merry Lester inadvertently did this year in her greenhouse. She grew kale and found it covered with aphids who pretty much left all of her other plants alone. Unfortunately, I can’t recommend particular host plants since many aphids are host-specific and there are hundreds of species of aphids.
If you are unable to adequately control aphid infestation with biological or mechanical controls, you may want to try insecticides. A systemic insecticide provides the best control by working within the plant. These are available in both spray and granular forms and are known by trade names such as Orthene (acephate), Cygon (dimethoate) and DiSyston. Merit (imidacloprid) is another systemic insecticide that is applied by commercial applicators directly into your garden soil. Never use these systemic chemicals on food crops. It’s illegal and unsafe. And always read and follow the directions on the label.
Other insecticides that work on contact include Sevin, Diazinon and Dursban, but they can be harmful to birds, bees and butterflies. It’s best to spray in early morning or late evening when these animals are less active and when the wind is less blustery.
Deb Babcock is a Master Gardener through Routt Extension office. Products mentioned in this article are not recommendations, but are provided solely for educational purposes. Call 970-879-0825 or email CSUMGProgram@co.routt.co.us with questions.