1994 Annual Report for FS94-019
Biological Control of Flower Thrips in Pepper Fields
Summary
Objectives
Since 1989, when the first specimen was identified in south Florida, the melon thrips, Thrips palmi, and the western flower thrips, Frankliniella occidentalis have become established in that area. Pepper plants are one of their preferred hosts, and they can cause devastating crop losses if left uncontrolled. Controlling these thrips without setting off secondary pest problems or accelerating resistance in other species is a problem soon to be faced by many vegetable and row crop growers as these pests spread. Conventional insecticides that can be used for control are known to eliminate beneficial insects, such as minute pirate bugs and parasitic wasps, which play a key role in managing thrips as well as other pests, such as armyworms. USDA entomologists predict that the range of Thrips palmi will extend north into Georgia, and west to the Pacific Ocean. Accordingly, nearly all of the nation’s winter pepper production is at risk.
The objectives were to:
1.) Monitor, collect and identify, on a twice weekly basis, fields and nurseries to determine insect (damaging and beneficial) populations.
2.) Test alternative pest management strategies. Compare costs, crop yields and crop quality of traditional commercial insect control practices to alternative, biological control practices.
3.) Test the use of predatory nematode Steinernema carpocapsae as a biological control agent for thrips.
To achieve these objectives, the researchers examined four specific areas, all related to biocontrol and pesticide use reduction. These included the use of different cover crops as predator nurseries, application of a predatory nematode to control adult thrips emerging from pupae, release of predatory insects to control adult thrips and the release of predatory mites to control broadmites.
Some of the experiments were hampered by tropical storm Gordon dumping over 12 inches of rain on the farm in November 1994. Regardless of the weather, results show that biocontrol was an effective alternative to relatively toxic pesticides in the on-farm trials.
Approach
Green Cay Farms raises 225 acres of green peppers each year along with 100 acres of squash and cucumbers. In the summer of 1993, participants planted clay peas and sorghum as cover crops in non-crop areas at Green Cay Farms. These had to be moved off shortly after bed preparation began, due to the tall growth of sorghum and weeds, which interfered with farm machinery. During the summer of 1994 the participants tried Alyce clover and Aeschynomene, both legumes, as cover crops. Rank growth of the latter resulted in these being mowed soon after peppers were planted. During both seasons, very few thrips or their predators were collected from any of these species. However, based on twice-weekly scouting reports from Glades Crop Care, Inc., an increase of several predator species occurred in the pepper crop shortly after the cover crops were mowed. This may have been coincidental with the seasonal incidence of these predators, or may indicate their activity was increased after being forced out of the legume cover crops by mowing.
The participants also monitored insect populations in a native weed species, Wedelia triloata, found growing abundantly on the ditch banks. This particular weed harbored large numbers of a non-destructive species of thrips, as well as predatory insects, and will be examined further in the future. Future testing of such nursery areas will include a more critical selection of cover crops. The researchers will be seeking plants with a prostrate growth habit that does not interfere with farming operations and that will continue to flower through Florida’s winter season.
In 1993 Glades Crop Care had tested an introduced beneficial nematode, Steinernema carpocapsae, at a pepper growing site in Charlotte County, FL. Results from that test showed significant reductions in emerging adult thrips, so the test was repeated on the grower’s farm with similar results. The nematode product was Biovector, manufactured by BIOSYS. This product turned out to be more economical than a mass release of predatory insects purchased from a commercial insectary. Emergence traps were sampled for thrips in both treated and untreated areas at seven and 14 days after treatment (DAT). In all cases, the areas treated with Biovector showed reduced numbers of emerging thrips.
Having heard of successful control of broadmites (a major pest of peppers) and western flower thrips at The Land in Disneyworld’s EPCOT Center using the predatory mite, Neoseiulus barkeri, the participants decided to try releasing this mite at Green Cay Farms. Release was made in October 1994, in time for a minor seasonal peak in western flower thrips.
The presence of the predatory mites seemed to have little effect on thrips populations or the damage they caused. Very few of the released mites were observed during regular scouting, and they did not satisfactorily control the broadmite infestation. Therefore, it was decided to apply a miticide to control broadmites, thus ending this release experiment. Weather or some other factor may have affected the field survivability of the predatory mite; however, the successful control achieved at Disneyworld makes the researchers think this control method is worth a second look.
The possibility of augmenting the beneficial insect population was investigated, particularly Orius insidiosus, a common, seasonal thrips predator and one that appeared soon after the cover crops were mowed. The collections indicated that this insect has seasonal peaks in mid-fall and again during the spring. During these peaks they exert significant control over thrips infesting some crops. However, they enter diapause during the short days of winter, thus removing themselves from the scene. A release in a quarter-acre plot was made in late December 1994, with a second release made two weeks later. The timing was arranged to see if Orius insidiosus would become established during this off season. Such establishment would offer the possibility of enhanced biological control of thrips later in the spring. Weekly examination of pepper blooms and growing points near the release site showed that very low levels of Orius insidiosus were present shortly following release. Although the crop was blooming abundantly at the time of release, foul weather and crop maturation caused a progressive decline in the numbers of thrips prey, and their tendency to enter diapause resulted in no recovery of Orius insidiosus during the last weeks of the monitoring period.
A preliminary review was made of the economics of the participants’ pest management practice, compared to those of other growers in the area. The participants found that the cost of their program was much less than those of their neighbors. The participants used primarily Bacillus thruingensis (B.t.) products and Neemix in their regular control program, with only one application of Lorsban, a relatively toxic pesticide, to control a large influx of armyworms in one plot.
Between the fall and spring pepper crops in 1994-1995, the participants had an average chemical cost of $251.95 per acre, while the average projected for Palm Beach County was $591.00. This average was obtained from the 1993-1994 "Production Costs For Selected Vegetables In Florida" circular published by the University of Florida. This translated to a chemical cost of $0.22 per package at Green Cay Farms as compared to $0.52 average for Palm Beach County.
If the growers look at both the economic and environmental costs of strictly conventional pesticides, the savings become much more dramatic. By moving to a biologically oriented spray program, the growers were able to decrease total chemical costs by over 68 percent. In addition, the worker risk factor for biological control is much lower than that of conventional pesticides.
Results
In conclusion, the research found that cover crops are helpful in providing refuges for predatory insects, but more covers with prostrate growth and a winter flowering period need to be identified. The predatory nematode Steinernema carpocapsae provided good control of emerging adult thrips, however, release of the two predatory insects, Neoseiulus barkeri and Orius insidiosus, were not very effective. Finally, the participants’ reliance on biocontrol products in their pesticide program was found to be very cost effective.
The success of the grower’s general IPM program, which closely integrates field scouting, cultural practices and the use of relatively safe pesticides demonstrates that economical pest control can indeed be achieved using these methods. When selecting cover crops in the future, the grower will carefully evaluate the growth habit of the species chosen. Particular attention also will be paid to the life cycle of the cover crop and how that relates to critical time periods in the vegetable crop, as well as habitat suitability for the target insects.
While the release of predatory mites and insects did not produce satisfactory control in these experiments, the literature indicates many successful examples exist. Environmental conditions may have adversely affected the particular predators that were released, so these particular species should not be dismissed as a viable control method. The application of Biovector proved extremely effective in reducing the number of thrips pupae emerging from the soil. Since a current method does not exist for providing dependable conventional chemical control, this may prove to be the best method currently available for Thrips palmi control.
Outreach
Participants made presentations at a vegetable growing seminar hosted by University of Florida Cooperative Extension Service and a monthly Extension Service meeting. They also assisted in a media workshop entitled IPM: In Partnership with Nature, which was sponsored jointly by the National Foundation for IPM and the International Food Information Council. In attendance were 25 food editors from around the United States, including CNN, Progressive Farmer Magazine and the Los Angeles Times.
December 1995.