Greenhouse Experiment

University of Wisconsin - River Falls

Dec. 12, 1997

UW-RF Launches Mites Greenhouse Control Experiment

By Justin W. Hancock
UW-RF News Bureau

As part of an experiment, a group of UW-River Falls horticulture students started a war in the University's greenhouse.

As part of a greenhouse management course, three species of beneficial mites were released into the foliage display house of the greenhouse recently to help combat of the most serious of greenhouse pests: the red spotted spider mite.

The red spotted spider mite is a major pest to greenhouse growers and homeowners alike. But rather than turn to chemicals to control the pests, the experiment tries another promising alternative. These mites species that were introduced are considered beneficial since they destroy insects that harm to the plants.

The introduced mites are an experiment and learning device at this point, and not a guaranteed answer to the spider mite problem. Organized largely by horticulture Professor Terry Ferriss and Dan Waletzko, greenhouse manager, the focus of the project was primarily to give students exposure to the use of beneficial insects.

With time, students will see the complex interactions that occur in the greenhouse between the environment, beneficial insects, pests, and plant species, Ferriss said.

One way for students to see this is by monitoring the numbers of "good" and "bad" insects. Ferriss said she hopes the students will be able to discern the benefits of the experiment and replicate it when they enter industry.

Although opportunities exist throughout the horticulture industry to implement programs, it may be a while before insects are used widely in commercial plant production.

Ferriss offered several explanations. First, to maintain beneficial insects there must be a food source, mainly the "bad" insects. Consumers don't like insect damage on their plants and are generally not tolerant of even minor damage the "bad" insects may cause. This limits the use of the "good" insects. In addition, many consumers are not comfortable with the concept of "crawly" things on the plants they bring home, regardless of whether they are beneficial.

Some of the locations where these insects may be more effectively used are in botanical gardens and conservatories, interior plantscapes, such as those found in some hotel lobbies, malls, and business complexes, and the fruit and vegetable industry. For those parts of the commerical plant world, perfection of plant specimens isn't as necessary, and in fruit and vegetables, the leaves where the insects reside are generally not harvested.

Another reason for a slow acceptance is that the insects can be difficult to maintain. Predatory mites such as those introduced at UW-RF prefer an environment that is warm and humid--almost completely opposite to the warm, dry environment preferred by the "bad" mites. The chemicals applied also need to be watched more carefully, to be certain that none of them negatively affect the beneficial mites. The two kinds of mites also prefer to live on different plants, which can also add to the challenge.

So far in the UW-RF experiment, it appears as if the "good" mites are winning the first battles, according to Waletzko. He said intial follow-up shows that there have been changes in the populations of "bad" mites. The challenge for Waletzko, Ferriss, and the students will now be to determine which of the "good" mites are winning the war, and exactly how effective they are.

The process of fine-tuning the program has just begun, as has the war of the insects.

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