By Jane Gregg, Colorado Master Gardener Boulder County
One of the earliest and most common garden pests is the aphid. We see them early in the spring because eggs, laid on the host plant in fall, hatch and the nymphs begin feeding just as new growth emerges. Although small, 1/8” as an adult, they can be found clustered together on the underside of leaves or on fresh sprouts or buds. Varying in color from light to dark, hundreds of varieties are found in Colorado that can affect trees, shrubs, gardens and grasses by sucking the nutrient-rich juices from the foliage. Some aphid species inject a toxin into plants, causing the leaves to curl. The curled leaves reduce the plant’s ability to absorb sunlight so it’s unable to produce energy. The aphid, however, produces a waste product referred to as ‘honeydew’. You may have noticed it as those sticky drops on your car when you park under an infected tree. With a large infestation, the honeydew can create additional problems by attracting ants, wasps and bees, and large areas of the foliage will often turn black from a sooty mold that forms.
Aphids are managed easily in most gardens though. They even have several natural predators like ladybugs and their larvae. Ladybugs can be purchased in most garden centers, and are a fun addition to any garden. Because aphids are soft-bodied and most are wingless, a firm spray of water will damage them or remove them from the plant. EPA- approved control products like topically applied detergent and soap sprays also are effective if they make contact with the insects themselves. These methods might need to be repeated for a few consecutive days. Trees and shrubs, however, can harbor infestations that will need other forms of management. Topical sprays and systemic treatments are available at garden centers, and, for trees, soil injections can be applied by a certified arborist.