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Biological Control Research Helps Address New Avocado Pests

The Issue

Two exotic pests, avocado thrips and persea mite, appeared in California in 1990 and 1996, respectively. A model based on 1998 harvest data predicted that growers in the state, who produce about 95 percent of the nation's avocado crop, would experience an estimated $13 million in short-term losses, with annual losses decreasing to $6 million as the industry developed means to deal with the pests. After more than four decades of largely pesticide-free insect control, many avocado growers now find it necessary to spray their orchards to minimize foliage and fruit damage.

What Has ANR Done?

Biological Control Specialist Mark Hoddle of the University of California, Riverside has worked closely with growers to develop biological control strategies to suppress avocado thrips and persea mites. Combating the mites involved three years of evaluation to identify an effective natural enemy, a predator mite known as Neoseiulus californicus that is raised commercially in California, and recommend for use by growers. Dr. Hoddle developed a motorized sprayer to apply the predator mites directly onto avocado tree leaves. The first step in controlling avocado thrips (Scirtothrips perseae) was to classify the pest and its home range, both of which were unknown until the pest became a nuisance in Ventura County in 1996. Dr. Hoddle also identified Franklinothrips as an effective predator species. Dr. Hoddle has successfully mass-reared these ant-mimicking predators, and has developed a new harvesting mechanism and automated sorter that makes it possible to collect predators from their rearing cages and transport them to groves. Field trials evaluating mass-reared Franklinothrips for control of avocado thrips are underway. Another method Dr. Hoddle determined to be useful to combat thrips is the use of composted organic mulches around the trees. Not only do the mulches aid in retaining water and benefit the soil, they also increase fruit yield by 13 percent and reduce populations of avocado thrips, which fall off trees to pupate, by as much as 50 percent. In addition, mulches help suppress avocado root rot.

The Payoff

Avocado Growers Given Safe, Effective Tools Against Invasive Pests

Persea mites can be largely controlled through non-chemical strategies developed by Dr. Hoddle. Biological and cultural control of avocado thrips that reduces reliance on pesticides has progressed substantially, and techniques developed at UCR are employed by growers. The benefits to the state's $300 million-a-year avocado industry include the curbing of significant financial losses due to damaged fruits. Urban residents living near avocado groves also benefit from non-chemical solutions, as do state growers, who are proud of their "green" tradition that relies more on biological control techniques than pesticides.

Clientele Testimonial

Guy Witney, Production Research Program Manager for the California Avocado Commission, notes that Dr. Hoddle's research has provided growers with greater understanding of these two new pests and has been key to identifying natural enemies and methods for rearing them. "Mark did a tremendous job of elucidating the natural biology and biological control of persea mites. . . . We do see flare-ups on occasion and sometimes growers will use narrow-range oils for control, but we are always on the look out for biological control methods, which Mark has done a great deal to provide."


Supporting Unit: UCR Department of Entomology

Dr. Mark Hoddle, 254 Entomology Building
UC Riverside, P(909) 787-4714, F(909) 787-3086
mark.hoddle@ucr.edu http://biocontrol.ucr.edu/