Guardian Plants are particular plants that draw pests away from crops and at the same time support the continuous reproduction of the pest’s natural enemies. The concept was developed indoors on greenhouse crops. In this trial, we attempted to transfer greenhouse guardian plant techniques into field vegetables for the first time. IPM Laboratories, Inc. collaborated with 1 New York farmer, 1 Niagara County Cooperative Extension agent, 2 professional scouts, and 1 Environmental consulting firm to evaluate marigolds as Guardian Plants for thrips in sweet pepper fields and snapbeans as Guardian Plants for spider mites in eggplant fields. Data were collected for 2 seasons: 2011 and 2012. Over the 2 year trial, the marigolds proved to be useful Guardians of the peppers against thrips while the beans did not give the same protection against spider mites in eggplants.
In 2010, Mark Zittel of Amos Zittel and Sons, Inc. experienced extremely high numbers of thrips on sweet pepper plants that they had transplanted from the greenhouse to a nearby field. Although they sprayed 5 times, they still experienced significant damage to the field.
In both 2011 and 2012, the thrips predator Orius established and reproduced on the marigolds prior to the peppers as evidenced by the presence of the first Orius nymphs on the marigolds. Thrips numbers remained quite low throughout both seasons compared to past experiences of the Zittels who in 2010 saw 5 or more times as many thrips despite repeated pesticide treatments. By the close of each year’s dataset, Orius numbers and thrips to Orius ratios in all pepper fields were utterly astounding. There were more than one Orius per sample where each sample was a small portion of a pepper plant. On July 26, 2011, there were less than 1 thrips per Orius on the peppers. In 2012 on July 5, there were about 1 thrips per Orius on the peppers. This ratio is extremely favorable given that Orius can kill 5 to 20 thrips per day. No thrips sprays were required in 2011 or 2012.
In another area of the farm, imidicloprid pesticide used in June to control Colorado Potato Beetle on eggplant devastates the spider mite predator population in June. With no natural suppression, the spider mites flare up and start bronzing the fields, often requiring 2 summer sprays for spider mites. Beans are particularly good trap plants for spider mites and can be planted in the middles of tractor lanes that are free of the pesticide. Predator mites released onto those beans in a July 2010 preliminary trial 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. We proposed to document the effect of using beans as Guardian Plants in eggplants.
In 2011 and 2012 the predatory mites established on the bean release rows and increased over the season. But where no beans were present, the predators established equally well on eggplant release rows. In both cases, predators were detected as far as 4 rows away from the row where they were released. The predators appeared to be extremely mobile and more numerous wherever the spider mites were more numerous. In this part of the trial, our beans did not provide the Guardian Plant services that we were hoping for since the treated eggplants usually appeared to have more predators than the treated beans. However, the number of miticide treatments was reduced from 3 sprays in 2010, to a half of the field sprayed once in 2011 and no sprays in 2012.
Mark Zittel has shared the discovery of abundant Orius in pepper and eggplant fields with all growers willing to listen on his own and neighboring farms, and they have found them almost everywhere that they have looked. A local pesticide representative even used the predators as a talking point. The project cooperators shared the project results at grower meetings, including a Western NY Vegetable Growers Meeting in Lockport, NY and the Mid-Atlantic Fruit and Vegetable Conference in Hershey, both in 2012. In August 2012, a twilight meeting on the Zittel farm was organized by Robert Hadad of the Cornell Cooperative Extension for grower Mark Zittel and Entomologist Carol Glenister to explain the project to area growers.
Our project was designed to be the first outdoor documentation of evaluating the potential of using Guardian Plants in field vegetables to pull pests out of crops and support natural enemy reproduction. We examined the ability of marigold Guardian Plant flowers to support early season Orius production until the field peppers developed flowers. We also examined the ability of snapbean Guardian Plants to support spider mite predator reproduction in eggplant fields until the pesticide imidicloprid wore off.
Although scientific research requires multiple fields and multiple farms, we proposed to concentrate our energies on in-depth weekly scouting of many plants in an individual field and compare them to the plants in a conventional field. The weekly scouting enabled us to track reproduction of the natural enemies. Reproduction is the single most important indicator of the predator’s continued ability to perform in the field. Furthermore, the in depth scouting would tell us how far the predators spread from the Guardian Plants so that we would have a better way to estimate how far apart Guardian Plants should be placed in the field. We felt efficacy trials in multiple fields were not appropriate until we had gathered baseline data with which to set up those trials. Thus, we tested the marigold Guardian Plant/pepper crop and the snapbean Guardian Plant/eggplant crop system in both 2011 and 2012.