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Photo: Scanning electron micrograph of a two-spotted spider mite feeding on a rose leaf. Link to photo informationClick image for caption and other photo information.

Rose Research Targets Mites, Powdery Mildew

By Marcia Wood
October 31, 2001

Spider mites and a disease called powdery mildew rank among the worst natural enemies of roses growing in greenhouses. But the Agricultural Research Service is helping these splendid plants fight back. ARS is among the sponsors of investigations at the University of California, Davis, that will yield effective, environmentally friendly ways to control mites and mildew.

The studies may help rose growers reduce the number of times they have to spray chemicals. Sometimes that's as many as 25 to 45 times a year, according to ARS plant pathologist Edwin L. Civerolo at Davis, Calif. He is ARS' representative for the greenhouse roses research.

The spider mite studies, conducted by Christine A. Casey and Michael P. Parrella of the University of California, Davis, will give growers new, science-based techniques for monitoring and sampling mites that infest rose plants. About the size of the period at the end of this sentence, spider mites use their mouthparts to suck out the contents of leaf cells. By removing cell components called chloroplasts, for example, mites interfere with the plant's ability to convert sunlight into food.

Investigations of powdery mildew will determine whether an early-warning system for forecasting outbreaks of this pathogen in vineyards can be successfully adapted to greenhouse production of roses. The monitoring system tracks environmental conditions that favor proliferation of grape powdery mildew. But grape powdery mildew is not expected to behave exactly the same as rose powdery mildew. So, researchers Linda L. Bolkan and James D. MacDonald at the university are fine-tuning the computerized, mathematical model that drives the grape mildew forecasting system so that it will be applicable to greenhouse rose production.

In addition to ARS, other sponsors of the research include the State of California Department of Pesticide Regulation; Roses, Inc.; the American Floral Endowment, and the California Cut Flower Commission.

ARS is the U.S. Department of Agriculture’s chief scientific research agency. Civerolo is at the ARS Crops Pathology and Genetics Research Unit.