Two-spotted spider mite (Tetranychus urticae) is a polyphagous mite that feeds on many crops. Because of its quick life cycle and ability to survive extreme conditions, it is one of the main pests found on most crops and ornamental plants. There are several factors that make two-spotted spider mites challenging pests:

• Adults can survive for long periods.
• They can overwinter as gravid female, allowing a rapid population growth in spring.
• They thrive in high temperatures.
• The webbing they can produce makes it difficult for beneficial insects and spray applications to penetrate.
• There are an extremely broad range of host plants for two-spotted spider mites.

Weather

The two-spotted spider mite is a master in surviving high temperatures and low humidity. This climate combination often results in a population explosion. Within one to two weeks, a life-cycle (egg to adult) can be finished and the newly hatched female has become a mother herself. To get a better understanding, each spider mite female leads to 140,000 newly hatched individuals in the third generation. This can be in three weeks’ time. Another reason this pest is the number one pest in many crops.

Control

Spider Mite Infestation (Photo credit: John A. Weidhass, Virginia Polytechnic Institute and State University)

Pesticide resistance in spider mites may be a serious issue unless proper integrated control strategies are followed. Using the right product or tool with correct timing results in a successful spider mite control program. To successfully control spider mites, the starting point is generally a clean crop. For example, a chemical application that has short persistency on predatory mites can be used to clean up the initial population. Seven days after this treatment, a release of the predatory mite P. persimilis (Phytoseiulis persimilis) can be done for a quick result and to clean up hot spots rapidly.

A. andersoni (Amblyseius andersoni) is a slower establishing predatory mite. When released in large numbers, it works to prevent development of the spider mite population. P. persimilis will provide better control on the spider mite hot spots and when released in combination with Amblyseius which works as a preventative strategy. They don’t interfere with each other and make it difficult for the spider mite to develop damaging populations. A strong advantage of A. andersoni is the successful use in outdoor crops. It performs well under a broad temperature range (43 to 100 degrees F) and can control the spider mite population before it creates a problem.

Spider mite control with predatory mites is successful due to high numbers of mites. It should be high enough to defeat the quick reproduction of spider mites. P. persimilis females lay eggs within a spider mite colony and feed rapidly all spider mite life stages. Their life cycle is completed faster than the spider mite life cycle allowing them to decimate the spider mite colonly. P. similis only feed on spider mite species. A. andersoni is slower to establish but tolerates lower humidity and has broad temperature tolerance range. It also will feed on thrips, pollen, honeydew and many species of mites, allowing the population to continue in the crop when the beneficial mite population is low. Chemical applications that will have a low impact on beneficials should be considered when spider mite populations over whelm the beneficial mite populations or as a cleanup application.

Spider mite control leans on both chemicals and beneficials. Start clean and introduce the right predatory mite at the right moment. Use P. persimilis for the quick result and A. andersoni mites for longer term.