Ashley Gregory

Let’s talk a little about some of the most common pests that we see in our home landscapes. I’m going to limit our focus to the three pests that I receive the most questions about: whiteflies, scale insects and mealybugs.

All of these are categorized as “Sucking Insects” because they feed by puncturing plant parts with long, strawlike mouthparts and removing sap, causing plant stress and a variety of symptoms. Since these insects are very small they concentrate in areas where the tissue is the softest, either on the underside of the leaves or the tender, new growth.

Plant symptoms are very similar for all three pests and often include wilted or off-colored leaves that look white or yellowish, stunted growth (especially in small plants), leaf drop and/or leaf deformation, branch die-off and in extreme cases plant death. Additionally, all of these pests excrete a sweet, sticky liquid while feeding, known as “honeydew”. This liquid can become a food source for fungus commonly known as “black sooty mold” and in abundance it can reduce the plant’s ability to photosynthesize.

White adults are 0.8-1.2 millimeter long with white wings (without markings) and pale yellow bodies. The wings are held in a roof-like position (about a 45-degree angle) over their bodies. Whitefly is a common pest of cotton, so populations are very high during August and September as all the cotton has been defoliated at this point and they are in search of new host plants.

They are a particular nuisance for tomatoes due to the fact that they transmit the Tomato Yellow Leaf Curl virus.

Scale insects are commonly misidentified, primarily because they appear to be nonliving; once the young settle on a plant, they usually don’t move and are often overlooked. They are generally small (1/4 inch long or less) and often mimic various plant parts, such as bark and buds.

Other species appear as small, white, waxy blotches or small bits of cotton on leaves and stems.

Mealybugs are small, oval and wingless. These insects have long tails and are covered with wax that makes them look fluffy and cottony. They like to settle in the protected crevices of plants, and because of their waxy coverings, don’t be surprised if you find these bugs difficult to control with insecticides.

In small populations you may not even notice these pests unless you are diligent in checking your plants regularly, especially the underside of leaves and the areas of new growth. Because these pests only cause significant damage in very high populations I only recommend chemical control in extreme cases.

Typically you can resolve issues with these pests by pruning off the infested parts, spraying them with your water hose on a medium to high pressure setting (depending on the plant) or by using horticultural oils or insecticidal soaps. Keep in mind that oils and soaps only kill pests that are sprayed directly. If you have to apply chemicals, take the time to learn about the life cycle of the pest; many chemicals are only effective during certain stages of development. To learn more about common landscape pests visit our Landscape Integrated Pest Management page.

Ashley Gregory is the Horticulturalist for Hidalgo County with Texas A&M AgriLife Extension Service. She can be reached at the Hidalgo County Extension Office at (956) 383-1026 or by email at ahgregory@ag.tamu.edu.

Silver leaf whitefly adults and enclosed pupae, a common pest of cotton. These insects are common between August and September. (Courtesy photo)
Mealybugs found on a leaf. (Courtesy photo)