There have been several reports of woolly aphid infestations in East Texas within the last few weeks. Woolly aphids are often described as being small white flying insects found on leaves. Just like all other aphids, they penetrate leaf veins and feed primarily on the phloem. In doing so, they excrete a lot of the excess phloem in the form of “honeydew” – a sugary solution which often ends up on nearby leaf surfaces or on the ground near the infested tree. A high level of infestation often results in a sticky ground and grass below the infested tree and the appearance of black sooty mold where honeydew has coated a surface. Black sooty mold will appear as a satin bumpy black substance (hence the name “sooty mold”) on the honeydew-coated surface.
Woolly aphids are often described as small white flies, however not all woolly aphids have wings. Some of the adults and all immature aphids do not have wings. A high level of infestation can be easily recognized by the presence of sticky surfaces caused by the aphid honeydew (i.e. their excrement) which also creates a favorable habitat for sooty mold. Woolly aphids should not be confused with whiteflies which, as their name suggests, are also small white flies, although management practices of whiteflies and woolly aphids are similar.
In low populations, aphids are often non-problematic. However, being parthenogenetic, aphids can reproduce at a very rapid rate and can overwhelm a plant. In large numbers, aphids can cause rapid wilting of plant leaves, reduce plant growth, reduce photosynthetic capacity (by covering leaves in sooty mold), and in some rare instances, cause plant death. Some aphid species can vector plant pathogens that can be much more harmful to plant health, but such pathogens are not currently considered a concern with woolly aphids.
Depending on the woolly aphid species, there are several different potential hosts. Before deciding to manage the aphid population, ensure that they are established and on a natural host. Like other aphid species, woolly aphids are often limited to their specific plant hosts.
Woolly aphids should only be managed when experiencing high damaging populations in the landscape, but early when populations are low in greenhouse high production settings.
Aphids have many natural predators, including lady beetles, syrphid fly larvae, green lacewing, and many types of parasitoids. These natural predators can sometimes be enough to manage the pest. Check for natural predator populations before choosing to spray an insecticide, as many insecticides are broad-spectrum, resulting in harm to beneficial insects as well as the pest.
If the infested plant is small and within reach, use a contact insecticide, such as insecticidal soaps or horticultural oils. Ensure that the spray makes contact with the aphids in order to be effective.
If the infested plant is large and out of reach, use a systemic insecticide. Search for insecticides with active ingredients such as “imidacloprid” or “dinotefuran”, and ensure that the insecticide is labelled for the particular pest, crop, and setting (i.e. indoor vs. outdoor) that suits your needs. Systemic insecticides are often applied as soil drenches and can take a few weeks to become effective, but will remain effective against any pests that attack the plant for a few weeks, sometimes even months.
When spraying insecticides, always read the label. Some are especially harmful to pollinators and cannot be applied when pollinator exposure is a risk.
Below are photos of a specific species of woolly aphid, known as the Hackberry Woolly Aphid (Shivaphis celti).