Control of spider mites in eggplants and thrips in field sweet peppers using guardian plants and predators

Control of spider mites in eggplants and thrips in field sweet peppers using guardian plants and predators

Summary

IPM Laboratories, Inc. collaborated with one New York farmer, one Niagara County Cooperative Extension agent, two professional scouts, and one Environmental consulting firm to evaluate marigolds as a Guardian Plant for thrips in sweet pepper fields and snapbeans as Guardian plants for eggplant fields. The 2011 season data has been collected and is now being analyzed. During the 2011 season, inspections of the experimental field and other nearby fields were also organized informally by local growers and a pesticide representative to see the predators in action. The project cooperators will be sharing the project results at grower meetings, including a Western NY Vegetable Growers Meeting in Lockport in late February and the Mid-Atlantic Fruit and Vegetable Conference in Hershey in February. Our project, when completed, will be the first outdoor documentation of Guardian Plants that pull pests out of crops and support natural enemy reproduction in vegetables fields.

Objectives/Performance Targets

In 2010, the Zittel farm in Eden, New York, experienced extremely high numbers of thrips and significant damage on pepper plants that had been transplanted from the greenhouse to the field despite 5 insecticide treatments. Beneficial insects are extremely successful at controlling thrips in greenhouse peppers because pepper flowers support continuous reproduction of the thrips predator, Orius insidiosus. In 2011, we proposed to test adding marigold Guardian Plants to pepper fields to pull thrips from the peppers and to support Orius reproduction until the peppers begin to flower and support Orius reproduction on their own.

In another area of the farm, imidicloprid pesticide used in June to control Colorado potato beetle on eggplants devastates the spider mite predator population, resulting in spider mite outbreaks that bronze the fields and require 2 summer sprays. In 2010, snapbeans were planted in the pesticide-free tractor lanes as trap plants for spider mites and reproduction sites for predatory mites. The predator mites spread at least four rows into the eggplants and suppressed the spider mites to a level similar to miticides in the rest of the field. In 2011, we proposed to repeat this planting scheme for a second year, under more controlled conditions, to document the success and usefulness of this IPM method.

Weekly scouting of pests and predators was planned to track the establishment and production of the released natural enemies (the single most important indicator of the predator’s continued ability to perform in the field). The in depth scouting was also designed to provide information on how far the predators will spread into the field from the Guardian Plants, so that we could plan how far apart to space the Guardian Plants in the field during future efficacy tests.

Success in the pepper/marigold Guardian Plant System would be demonstrated by the following:
• There will be evidence of Orius establishment and reproduction as indicated by the presence of Orius nymphs in the marigold beat samples.
• The marigolds will draw thrips away from the pepper plants, resulting in few thrips on the peppers and obvious thrips on the marigolds.
• The Orius will keep the thrips numbers from exploding on the marigolds.
• As the peppers begin to flower, the Orius will transfer over to the pepper plants and reproduce on them as well.
• Thrips numbers will subside with the expanding natural enemy population.

Success in the eggplant/snapbean Guardian Plant System would be demonstrated if the following questions can be answered by the weekly scouting data:
• Will the predators establish on the bean release rows as evidenced by increasing numbers over the season? And, if so, how far will the predators spread from the bean release row?
• If there are no beans, will the predators establish on the eggplant rows onto which they were released? And, if so, how far do they spread from the release rows?
• What are the spider mite and predator levels on the bean rows, the eggplants in rows adjacent to the release sites, eggplants 2 rows away, and 4 rows away?
• What are the spider mite and predator levels on the eggplants that had predators released onto them directly and control eggplants that received no predators?

Accomplishments/Milestones

Pepper/marigold Guardian Plant System
Weekly scouting on the peppers and marigolds was begun in the greenhouse in April, recording whole plant inspections for thrips and aphids. Orius was released onto the marigolds 2 times in the greenhouse, but there was not obvious Orius establishment in the greenhouse before the marigolds and peppers were transplanted to the field in June. The marigolds were placed in the field in two spacings (one per row and groups of 30) amongst the pepper plants. Two more releases of Orius were made directly onto the marigolds in the pepper fields during the weeks of June 6 and June 13.

Scouting in the treated pepper fields concentrated on counts of number of flowers, thrips nymphs, thrips adults, Orius nymphs, and Orius adults from beat samples of 50 pepper plants and 30 marigolds per treatment. The results were charted on graphs of weekly plant observations in terms of number of thrips and Orius per beat sample on the marigolds and on the peppers.

A second pepper field, under conventional pesticide management, was also scouted weekly in the same manner as the treated field. The conventional field did not receive Orius.

Preliminary inspection of the data revealed:
• Orius nymphs began to appear on the marigolds approximately 2 weeks after their release in the field, and both nymphs and adults increased over the season, thus demonstrating establishment.
• Thrips were approximately 3-fold higher on the marigolds than on the peppers, Thus the marigolds appear to be serving as trap plants. The highest number of thrips was recorded on the peppers in the conventional field where no marigolds were planted (7-fold higher than on the marigold/pepper treatments).
• At their peak, thrips on the peppers in the conventional field were approximately 2-fold higher than the peak level of thrips on the marigolds, indicating that the Orius appeared to be keeping the thrips numbers from exploding on the marigolds.
• Both Orius adults and nymphs were found on the pepper plants in late June, approximately 2 weeks after the peppers had begun to flower. Thus Orius will transfer to pepper plants and reproduce on them. However, it was clear from the numbers of Orius present in both in the experimental fields and surrounding fields that they could not have all come from just the released Orius. Thus, the marigolds supported a naturally-occurring population of Orius as well as well as the commercially produced Orius.
• Under all treatment schemes (blocks, singles, and no marigolds) in both the marigolds and the peppers, thrips nymph levels declined to zero with the expanding Orius population, however the correlation between rising Orius numbers and adult thrips levels is less clear and will require further analysis.

Eggplant/snapbean Guardian Plant System
The eggplant field was treated for Colorado potato beetle with imidicloprid via trickle irrigation about June 1 and esfenvalerate spot sprays in mid June. In July, the field was divided into 4 experimental sections and the following treatments were applied: 1) snapbeans planted in the driving lane and treated with predators, 2) snapbeans planted in a driving lane but not treated with predators, 3) predators applied directly to the eggplants with no beans present, and 4) eggplants with no beans and no predators.

Two thousand N. fallacis predators per row were applied on three rows of beans when spider mites began to appear on the beans in late July. The release was repeated once 2 weeks later. Likewise, 2000 predators per row were applied on three rows of eggplants to assess if the predators could establish without the beans.

Weekly scouting on the eggplants and snapbeans began in early August and lasted through mid September. However, in late August, most of the treated eggplants were sprayed for mites with Agrimek and Nufilm P. The scouting results were charted on graphs of weekly plant observations in terms of levels of spider mites and numbers of N. fallacis on 10 to 20 spider mite damaged leaves in each of the 4 experimental field sections. An exit survey was performed in mid September that included the above.

Preliminary inspection of the data revealed:
• Predators were detectable on the bean release row 2 weeks after their last release and increased on the release row 2.4-fold during the course of the season. During the exit survey, predators were detected on eggplants 1, 2, and 4 rows away at levels 2.8-fold higher, 0.8-fold lower, and 0.6-fold lower than the release row, respectively.
• In the field where no Guardian Plant beans were planted, predators were detectable on the eggplant release rows 1 week after their last release and increased on the release row 8-fold during the course of the season. During the exit survey, predators were detected on eggplants 2 and 4 rows away at levels 0.5-fold lower and 0.7-fold lower than the release row, respectively.
• At the end of the season, the exit survey data showed that the spider mite levels on the eggplants 1, 2, and 4 rows away from the bean release row were 2.5-fold higher, 1.5-fold higher, and 2-fold higher that spider mite levels on the bean release row. The untreated control eggplant field had spider mite levels 4-fold higher than the bean release row. The untreated bean control row showed no spider mite infestation.
• At the end of the season, the exit survey data showed that the control eggplants had spider mite levels 1.8-fold higher than the eggplants in the release row.

Impacts and Contributions/Outcomes

Our 2011 results indicate that the predators established on the field along with the pests, migrated from the Guardians into the crop, and helped to suppress the pests. The pepper/marigold Guardian Plant System appears to have been a success and will be the first outdoor documentation of Guardian Plants that pull pests out of crops and support natural enemy reproduction in field vegetables. Because spider mite levels rose during the season such that the fields had to be sprayed, the snapbean/eggplant data is not as clear and will need to be repeated a second season.

The Zittel family was deeply involved in this project. Mark Zittel made all the applications of beneficial insects and became proficient at spotting Orius in the field. In mid-July, he noted that Orius was naturally occurring in 1 out of 3 eggplant flowers, noting that there were up to 30 flowers per plant. This created impromptu Orius-scouting sessions on the neighboring farms. The local pesticide salesman, an unexpected contributor, Russ Yoho, even spread the word about the presence of Orius in vegetable fields. Mark Zittel and Carol Glenister will present the 2011 results at a Western NY Vegetable Growers Meeting in late February.

Collaborators: