.. I' X A Gulf Coast Research & Education Center Dover
 FVLO IDA 13138 Lewis Gallagher Road, Dover, FL 33527
 Dover Research Report DOV-1994-1
 Institute of Food and Agri Itural Sciences June 1994

 MANUAL OR BIOLOGICAL CONTROL OF TWOSPOTTED SPIDER MITES
 ON STRAWBERRY IN FLORIDA

 M. van de Vrie and J. F. Price

 Introduction
The twospotted spide mite, Tetranychus urticae Koch, is a major pest on
strawberry crops in lorida. Foliage damage by spider mite feeding often
results in reduced p ant vigor and berry production. Reliance on miticides
has become increasing ly difficult because spider mites develop resistance to
miticides, an import nt miticide has been withdrawn from the market, and
manufacturers are rel ctant to make the large investments necessary to
register new miticide on the relatively minor strawberry crop. Furthermore,
the application of mi icides can conflict with the harvest schedule. Mite
problems intensify du ing January through April when berries often are
harvested twice a wee.

Several disadvantages re associated with the use of miticides. They are
expensive and effective chemical spider mite control is difficult because good
coverage of the under des of the foliage is almost impossible to obtain.
This is especially tru when the older leaves contact with the plastic mulch.
In addition, as plants grow they form an almost closed leaf canopy, thus
making thorough cover e even more difficult.

To some extent, spider ite problems are the result of the application of
broad spectrum insecticides which are detrimental to natural enemies of spider
mites and insect pests. Elimination of natural enemies, which are commonly
present in undisturbed abitats, leads to a rapid development of spider mite
populations. Because o the absence of competition with other plant feeding
organisms and leaf disea es, the conditions for spider mite development are
excellent.

Research at the Universi y of Florida's Gulf Coast Research and Education
Center, Bradenton and Do er, in cooperation with growers and a commercial
scouting company has dem stated that biological control of the twospotted
spider mite by releasing he predatory mite species, Phvtoseiulus persimilis,
is feasible in commercial strawberry production. This manual outlines the
procedures developed for biological control of the twospotted spider mite. It
includes directions for m nitoring spider mite and predatory mite populations,
handling the predaceous mites, and integrating biological mite control with
standard practices of inse t, mite and disease control. This manual should
assist the field manager o scout and should help to ensure success with
biological control.

'Visiting Research Scientis and Associate Professor, respectively.