Testing the Efficacy of Alternative Methods of Whitefly Control in Organic Vegetable Production

Testing the Efficacy of Alternative Methods of Whitefly Control in Organic Vegetable Production

Summary

Whiteflies, including the sweet potato whitefly, the silverleaf whitefly and the greenhouse whitefly attack a broad range of economically important vegetable and field crops, and have recently increased in importance in the western and southern United States. Whiteflies damage crops by feeding on plant sap. More importantly, whiteflies are capable of transmitting viruses to a wide range of crops.

Biogeographic surveys of whitefly populations from 1989 to the present indicate that whiteflies inhabit nearly every major agricultural locale in the southwestern and southeastern states and Hawaii. Economic crop losses due to whiteflies and their associated viruses have been especially significant in Florida, Georgia and South Carolina. An important factor responsible for the whitefly’s prevalence in agricultural areas is its ability to feed, multiply and survive on an extremely wide range of host plants.

On their certified organic farm in Florida, the producers observed large whitefly populations during the entire cropping season. They experienced nearly 100 percent virus infection of snap beans and tomatillo. Overall, the viruses transmitted by whiteflies are their largest production problem.

Pesticide application is the most common method of whitefly control on conventional farms. However, organic farmers interested in alternative approaches have more limited methods available for whitefly control. In this research project, the producers will conduct an on-farm experiment to determine if an economically feasible control program utilizing an integrated pest management approach can be developed for small to medium-size farms.

Objectives
1.) Determine if the use of reflective mulches under beans is an effective means of whitefly
control.
2.) Determine if intercropping beans with squash is an effective means of whitefly control on beans.

Approach
The plot size is 10 feet long with four treatments/plot. Each plot is replicated four times giving a total of 16 treatment-replications. The producers are comparing both the number of whiteflies and the percentage of virus infection on beans planted under the following treatments:
1.) beans planted on bare soil,
2.) beans planted on plastic mulch,
3.) beans intercropped with squash and planted on bare soil,
4.) beans intercropped with squash and planted on plastic mulch.

The squash is utilized as a trap crop planted with the beans because squash is very attractive to whiteflies. The beans were inspected for symptoms of viral infection on a weekly basis. Whiteflies were sampled once a week in the early morning when they were less active. At maturity, all of the bean plants were harvested and weighed for each treatment.

Results
Reflective mulch may be more effective at deterring whiteflies early in the season before it becomes soiled or shaded by growing plants. It also was more effective when the whitefly populations were low to moderate; when the populations were high the reflective plastic mulch was less useful. The reflective mulches did help with soil moisture and weed control and by reducing nitrogen volatilization.

The squash served as an effective trap crop for whitefly when the populations were low to moderate. However, when the whitefly populations were high, the squash plants were still an attractant but the beans were also covered with whiteflies.

Outreach
Project results will be submitted to agriculture and plant pathology journals and papers presented at the Florida Plant Pathology Society or the Florida Entomological Society. The producers held a field day for local growers, Extension workers and master gardeners.

December 1998.