Insect Management: Identification and Control

A variety of factors can influence how a plant performs especially insects. Plants show different and sometimes similar biotic (biological) or abiotic signs and symptoms, but the biotic are usually easier to determine. Common insects that I frequently see customers having problems with are aphids, mealybugs, and scale.
Aphids occur on houseplants and outdoor plants. They can be hard to identify as they vary in color depending on their food source, but they don’t move when they are disturbed. They feed through a proboscis (piercing sucking mouthpart) that pierces the food conducting tissues and starves the plant. They attack in colonies focusing on the concentrated areas of sugars such as the terminal buds on the undersides of leaves or stem. The plant will begin symptoms of yellowing, new growth becomes distorted such as leaf curl, and growth is stunted.
Common mealybug species are distinct in appearance due to looking more like a microscopic fungus than an insect. It is small, round to oval shape with a white, waxy covering that acts as a protective layer looking somewhat like bird droppings. Plants will show symptoms of leaf yellowing, stunted growth, and sometimes small brown dots sprayed throughout infected leaves. They hide in protective areas and can be very unnoticeable until symptoms finally show or upon regular examination of the plant.
Scale is the next culprit. It doesn’t appear to look like an insect because of their hard exterior and barnacle-like appearance. Once the insect has started siphoning the sap from the plant, it remains anchored there. There are two types, the soft and the armored. The soft type produces a waxy or cottony exterior, similar to the mealybug, but remains smooth and tough. The armored type creates a hard exterior. They can be found throughout the plant. If left untreated, the plant will die.
Honeydew, a sticky sugary liquid is another key sign left behind by aphids, scale, and mealybugs eating sap. This is a rich food source for ants which helps keep natural predators away. Honeydew invites secondary problems such as black sooty mold fungus. The fungus does not attack plant cells but the black tarry substance formed over the leaves hinders photosynthesis. It does not come off easily. Soapy water mixtures may help, pruning, or even a high-pressured hose but this could damage the plant more.
I suggest using organic controls such as organic sprays or removing by hand before using any chemically based insecticides. Dormant oils are the first defense to use in spring. The oils are applied during bud break as temperatures begin to warm up. The oils kill the insects by clogging the tracheal tubes they breathe through their bodies. Insecticidal soaps will help kill aphids, young scale, mealybugs, mites, and other soft bodies insects, but certain plants are sensitive to it. Homemade concentrations can be made, but store-bought brands are more targeted. Both dormant oil and insecticidal soaps have less side effects on beneficial insects. Pyrtherins is a more general insecticide derived from chrysanthemums that is harmful to many insects especially honey bees. Spray this product early in the morning before pollinators are out. Use all products according to their label. Ingredients and instructions can change year to year. Even though these mentioned products can be safer than conventional methods of insecticides, there is potential for side effects to you, the plant, and the environment.
Written by Lauren Popper, horticulturist at Cape Shore Gardens and graduate of Temple University’s School of Environmental Design.