Scotts Professional Horticulture

By Raymond Cloyd, Ph.D.
Professor, Extension Specialist in Ornamental Entomology/Integrated Pest Management
Department of Entomology, Kansas State University/K-State Research and Extension

Whiteflies and spider mites are two of the most destructive arthropod (insect and mite) pests of horticultural crops grown in greenhouses. They both damage plants by feeding within the plant tissues. However, their feeding behaviors are different. Whitefly nymphs and adults feed within the phloem (food-conducting tissues) of plants using their piercing-sucking mouthparts. They remove plant fluids from the phloem sieve tubes, and because whitefly nymphs ingest large quantities of plant sap, any excess is exuded as honeydew, a clear, sticky liquid. Honeydew serves as a growing medium for black sooty mold fungi. The larvae, nymphs and adult stages of spider mites, in general, feed within plant cells, damaging the spongy mesophyll, palisade parenchyma and chloroplasts. This reduces the plant’s chlorophyll and moisture content as well as its ability to photosynthesize. Obviously, this situation creates serious ramifications for the plants themselves.

The primary means of dealing with populations of whiteflies (e.g., greenhouse and sweet potato B-biotype whitefly) and spider mites (e.g., two-spotted spider mite) is the use of pest control materials—in this case, insecticides and miticides. It is important, however, for greenhouse growers to understand the life cycles of each pest and the respective life stages that are susceptible to commercially available insecticides and miticides. The life stages of whiteflies include eggs, nymphs, pupae (fourth instar nymphs) and adults. The life stages of the two-spotted spider mite include eggs, larvae, nymphs (protonymph and deutonymph) and adults.

The time it takes to complete development from egg to adult varies from two to four weeks; however, this is dependent on ambient air temperature and, often, even the leaf surface temperature. As the ambient air temperature increases, it takes less time to complete the development cycle from egg to adult. For example, at 85ºF (29ºC) two-spotted spider mites can progress from egg to adult in approximately seven days. The life stages that are susceptible to most pest control materials are the larvae, nymphs and adults. No pest control materials will kill whitefly pupae, and there are only a few commercially available pest control materials that are active on the egg stage of both whiteflies and spider mites.

Controlling and Regulating Whiteflies and Spider Mites

What methods are best suited for controlling or regulating whiteflies and spider mites? These pests are most often managed using commercially available miticides and insecticides. For example, pest control products from Scotts Professional that are labeled for control or regulation of whiteflies and/or spider mites include Sanmite® and Ovation®.

Sanmite, which contains the active ingredient pyridaben, is labeled for both whiteflies and spider mites. Specifically, Sanmite is registered for control or regulation of two-spotted spider mite, broad mite, European red mite, Southern red mite, tumid mite and whiteflies. This product is a contact insecticide/miticide only, so thorough coverage of all plant parts (e.g., leaves and stems) is important for effective control or regulation. It is most effective on these pests when they are in the larval and nymphal stages of development. Sanmite quickly kills the mobile life stages, although its effectiveness is contingent on plant growth and the population dynamics of both whiteflies and spider mites (the interaction between the pest populations and environmental factors that may influence them). The label rate is 4.0 fl oz per 100 gallons. Sanmite has a mode of action that is similar to fenpyroximate (Akari®) and acequinocyl (Shuttle™). All three products are Mitochondria Electron Transport Inhibitors (METIs). However, the site of action of Sanmite and Akari is different from Shuttle. Sanmite’s mode of action involves inhibition of complex I (NADH; ubiquinone oxidoreductase) of the mitochondrial respiratory pathway, which reduces energy production by preventing the synthesis of adenosine triphosphate (ATP).

Ovation, which contains the active ingredient clofentezine, is labeled for control or regulation of two-spotted spider mite, Pacific spider mite, McDaniel spider mite, European red mite and yellow spider mite. Ovation is also a contact miticide, so thorough coverage of all leaves and stems is critical during application. This miticide is primarily active on spider mite eggs and the immature stages such as the larvae and nymphs, with no direct activity on adult spider mites. However, it is mainly used as an ovicide (egg-killer). Although Ovation is slow-acting, it may provide up to 45 days of residual activity, contingent on plant growth and the population dynamics of spider mites. The label rate is 2.0 fl oz per 100 gallons. Ovation has the same mode of action as hexythiazox (Hexygon®), which means that these two miticides should not be used in succession in a rotation program. The mode of action involves disrupting the formation of the embryo during development or inhibiting larval maturation. However, the specific mode of action and target site of activity are still not well understood. Greenhouse producers may tank-mix Ovation with a miticide that has adult activity in order to broaden the spectrum of control or regulation to include all the life stages—from egg to adult—of two-spotted spider mites.

When using these products, growers should be sure to scout all crops on a regular basis using yellow sticky cards and conducting visual inspections in order to detect infestations early. This process will help growers avoid the unpleasant situation of dealing with populations that have reached outbreak proportions. When applying either Sanmite or Ovation, it is imperative to ensure thorough coverage of all aboveground plant parts since most life stages of both whiteflies and spider mites are located on leaf undersides. Also, it’s necessary to apply pest control materials frequently enough to kill the pests that were in non-susceptible life stages (e.g., eggs and/or pupae) during the previous application. Finally, it is highly recommended to rotate pest control materials with different modes of action so as to avoid or delay the onset of resistance developing in whitefly and two-spotted spider mite populations.

Click here for MSDS, specimen label and other information about Sanmite® and Ovation®