A new integrated pest management (IPM) program for cut roses has dramatically reduced the volume of pesticides sprayed in California greenhouses and launched a successful biological control of spider mites, scientists report in a peer-reviewed study published in the April-June 2007 issue of the University of California's California Agriculture journal.

"This program represents the first and largest effort to demonstrate and implement an IPM strategy on floriculture crops in the United States," the authors wrote. "We have shown that high-quality roses can be produced with substantially fewer pesticides and with the incorporation of biological controls into mainstream floriculture."

In the mid-1990s, California rose growers reached a crisis point when pesticide resistance, costs and limited pesticide availability threatened growers' ability to effectively manage twospotted spider mites, one of the most important pest of cut roses grown in greenhouses. The study - conducted with eight commercial growers in San Diego, Santa Barbara and Santa Cruz counties - showed that a predatory mite called Phytoseiulus persimilus could effectively and economically control twospotted spider mites. The growers applied vials of P. persimilus (containing 2,000 predators each) when between 10 percent and 25 percent of randomly sampled rose leaves were infested.

To control western flower thrips, another important pest of cut roses, growers switched to commercially available, reduced-risk pesticides and targeted lower-volume sprays to just the upper canopy of the hedge (at 70 gallons per acre) - where thrips are most prevalent - rather than the full-volume wet sprays (at 275 gallons per acre) typical in conventional cut-rose greenhouses. The growers also implemented cultural controls such as removing fully open flowers, where thrips lay their eggs.

The program for cut roses was the result of a state-sponsored partnership among cut-flower growers, scientists and pesticide regulators. Since the 1970s, the University of California has been a global leader in promoting IPM, which bases agricultural pest-management decisions on economic thresholds and encourages the strategic use of biological, cultural and chemical controls in order to limit environmental impacts.

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