The Tomato Magazine

The Tomato Magazine
October 2006

Florida Industry Remains on Alert for Silverleaf Whitefly Biotype Q

Although biotype Q of the sweetpotato whitefly has not been found in any Florida tomato fi elds, it represents a new threat to vegetables and other crops in Florida.

Speaking Sept. 6 during the Florida Tomato Institute in Naples, Fla., David J. Schuster said biotype Q has been found in greenhouses and nurseries in 22 states, including Florida.

The concern, of course, is that it eventually will spread into tomato fields. Biotype Q is the most prevalent sweetpotato whitefly biotype in the Mediterranean region, he reported, and has plagued greenhouse-grown crops in southern Spain for years. This biotype is resistant to many of the commonly used insecticides for managing whitefl ies, including the pyrethroids, neonicotinoids, pymetrozine and insect growth regulators.

On top of that, resistance to biotype Q is more stable than that in biotype B, the key pest of tomatoes in southern Florida. Resistance does not diminish over time.

“A resistance management working group was formed in 2003 to promote resistance management on a regional basis,” Schuster said. “The group modified previous resistance management recommendations and met with growers to encourage their adoption. The working group consisted of University of Florida research and extension personnel, representatives of the chemical companies marketing neonicotinoid insecticides, representatives of commodity organizations and commercial scouts.”

Because of the threat of biotype Q and decreased insecticide susceptibility, the group was expanded and met in May, 2006, to once again discuss and revise the whitefl y and resistance management recommendations. From those discussions, field hygiene and cultural practices were identified as being a high priority and should be included as an integral part of the overall strategy for managing whitefly populations, Tomato yellow leaf curl virus (TYLCV) incidence and insecticide resistance.

“These practices will help reduce the onset of the initial infestation of whitefly and lower the initial infestation level during the cropping period, thus reducing insecticide use and selection pressure for insecticide resistance development,” the researcher said. “The recommendations also include insecticide use recommendations which help improve whitefl y and resistance management.”

Mandatory Burndown Rule
One outcome of the whitefl y, virus and resistance management discussions has been the proposal of a mandatory “Tomato Plant Destruction” rule by the Florida Department of Agriculture and Consumer Services, Schuster told the group. The proposed rule was coordinated by the Florida Tomato Committee and mandates that, within five days following final harvest of a tomato crop, commercial tomato producers “destroy remaining tomato plants on the production site.”

They are to use chemical burn-down with a contact desiccant-type herbicide that is EPA labeled and approved for this use, he explained. An example of an approved product would be paraquat. The herbicide should be combined with a minimum three percent oil and a non-ionic adjuvant to enhance destruction of the crop as well as to reduce the number of whitefl ies present which could migrate to nearby crops. Crop destruction must be followed by immediate complete destruction by crop removal unless double cropping is planned.

The proposed rule also contains a provision providing for enforcement, the speaker said.

“This proposed rule is agreeable to most growers and is the first attempt to manage the whitefly/virus situation in tomatoes by regulatory enforcement,” Schuster said.

“Some growers support defined, mandatory crop-free periods in the summer while others do not. If progress is not made in the management of the silverleaf whitefl y and associated TYLCV, pressure may build for a regulatory rule stipulating crop destruct and crop planting dates.”

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