Aphids

Another annual pest of concern to Colorado trees and gardens is the common aphid. There are dozens of species of Aphids in our region and virtually no plant is immune to their damaging effects. Aphids, similar to pine needle scale, are sucking/piercing insects that slowly drain a plant of nutrition. To make matters worse they take this nutrition directly from its production source, the leaves. The sole purpose of leaves to a plant is to produce food. This food is then transported to the roots for storage to be called upon the following spring as the tree emerges from winter. Without this reserve the tree is unable to produce leaves of sufficient size thereby reducing its ability to make food, creating a viscous cycle. Each following year the leaves grow smaller and eventually stop altogether. Left alone, and in sufficient quantity, Aphids lead to a plant’s decline and eventual starvation. Aphids are very small insects and tend to avoid detection by the untrained eye. In fact, it’s typically not the insect that generates calls of concern. Rather, it’s “sticky stuff on my patio furniture” that initiates the majority of phone calls to our office. Mountain pine beetle has enjoyed a great deal of media attention over recent years and even pine needle scale to a lesser extent. Aphids are the exception, however, and quietly go about their lives doing significant harm to the landscape’s components. They start to draw attention to themselves after a few seasons when the landscape no longer appears as healthy and vigorous as it once did. Trees exhibit yellowing leaves mid-summer and leaves become progressively smaller each season. There may be fewer leaves, and in extreme conditions the tree may be forced to drop its leaves prematurely (sometimes as early as July and August) in hopes of ridding itself of the pest. Each of these items should be taken as a cry for help from the tree.

Aphids are usually less that 1/8” in size and vary in color between species. Their populations increase dramatically with the return of warmer, summer weather and drop off suddenly with the first killing frost of autumn. Through their feeding activity Aphids create a by-product known as “honeydew”. This sticky substance is highly nutritious and has the consistency of corn syrup (and is nearly as sweet). It falls to any lower surface and tends to build-up on leaves, branches, patio furniture, car windshields, sidewalks, and even other plants. The presence of this honeydew, being so nutritious, results in the rapid development of mildew called sooty mold. Similar to what’s found in a humid shower, sooty mold produces a “peppered” look on surfaces. Honeydew and the resulting sooty mold don’t cause any real damage but can become a general nuisance and cleanup headache. Though when the sooty mold accumulates on leaf surfaces it can actually inhibit photosynthesis and cause stunting of growth.

Here’s the good news: Aphids are a fragile, easily controlled insect. They are so fragile, in fact, that many gardeners simply wash them off with a garden hose. Beyond just a simple stream of water there are a variety of products available for the control of Aphids. There are traditional, foliar sprays, systemic injections, and even beneficial insects such as ladybugs that offer consistent control. While it may be easy to treat low-lying plants and flowers you will want to consider hiring a professional for trees. Their equipment allows for a safe and thorough treatment and increases the chances for success.