9/28/2022 - By Robby Clemenzi

Thousands of mite species feed on and cause damage to plants grown in commercial production. Although mites are often grouped with insects, they are arachnids and more closely related to ticks and spiders than other common insects. Adult mites have eight legs and piercing-sucker mouthparts used to suck fluids from host plants. In addition to direct damage, mites are capable of transmitting plant viruses making mite management critical in commercial production settings.

The most common mites affecting ornamental plants in greenhouses and nurseries are spider mites, but what are they, and why are they so bad for plants?

Detecting Mites in Greenhouses and Nurseries

Most mites are tiny and require a hand lens (such as a magnifying glass) to be seen, making them difficult to detect in the absence of symptoms. In fact, some mites, particularly Eriophyid mites, are so small that they require a microscope to be seen. Immature mites in the larvae stage have only 6 legs, the exception is Eriophyid mites, which have four legs in all stages of development.

Most mites favor hot and dry conditions and can multiply rapidly with generations occurring within one week. Because of the vast variety of mites that have developed over time, nearly all plant species have at least one species of mite that will feed on them, including annuals, perennials, bulbs, vegetables, trees and shrubs.

Sign of Mites

Mites can be introduced on infested plant material, but often, they are introduced into production facilities by the wind. Most mites damage plants by sucking cell contents from leaf tissue where the initial feeding damage appears as a stippling of tiny dots on the surface of affected leaves. Heavily infested leaves and branches may be covered in fine silken webbing (i.e., spider mites), but webbing may be minimal on some plants, such as conifers, or completely absent on others. Severely affected leaves turn bronze to yellow in color and eventually drop off the plant.

Greenhouse and Nursery Mite Prevention

Frequent inspection of plant material is essential to prevent rapid buildup of mites in nurseries and greenhouses. This includes thorough inspection of new plant material for mites (and other pest and diseases) prior to moving them into production areas. Additionally, many weeds are susceptible hosts for mites and should be removed or controlled with herbicides.

Remove weeds and escaped plants under benches, outside greenhouses, or adjacent to nursery stock to reduce the likelihood of mite infestations in growing areas. Also, minimize plant disposal sites to prevent mite infestation even on plants which are out of the way.

Cost effective mite management begins with preventive applications and rotating miticide modes of action between applications. Refer to product labels for additional information and see the chart below for an example of a control rotation.

For more information on any products or tips mentioned in this article, reach out to your local Harrell's rep.