Controlling Western flower thrips in peppers and tomatoes increasingly relies on a many-pronged integrated pest management program with new, promising pieces.
Dubbed the "push-pull strategy," the approach focuses on pushing the pest, which vectors major diseases such as tomato spotted wilt virus, away from the target crop and pulling in additional predators such as minute pirate bug.
One already proven piece of that strategy is the use of ultraviolet-reflective mulch, says Joe Funderburk, professor of entomology at the University of Florida's North Florida research lab in Quincy.
"It works really well for a lot of day-flying insects," Funderburk says.
Many growers have adopted reflective mulches for their aid in pest management as well as their horticultural benefits. When temperatures climb, the light-bouncing fabric helps keep soil cool enough to show a yield bump, he says.
That aspect can be a mixed blessing, however. Winter use, for example, can turn soil too cool for pepper roots, he says.
Growers soon may be expanding their push-pull efforts with companion plantings and sprays of a kaolin clay-based material, based on two years of small-scale research.
"I'm convinced they'll play a big role in the IPM system in the future," he says.
This year Funderburk and his team plan to step up their study to field trials in 5- to 10-acre commercial plots.
Clay spray helps repel thrips
Spraying Surround—a crop protectant that incorporates kaolin clay—appears to have the strongest deterrent effect on Western flower thrips, says Kara Tyler-Julian, a master's student working with Funderburk at the Quincy lab.
But because it also repels minute pirate bugs, growers may need to use it only early in the season until scouting turns up predators in the fields, Tyler-Julian says.
Galen Frantz, senior crop management specialist at Glades Crop Care Inc. in Jupiter, says the use of Surround and reflective mulch during the pepper trials yielded no discernible thrips damage and "very little" overall insect damage—without insecticide sprays.
Yields showed no differences between the test and control plots, he says.
Not all thrips are created equal
Florida flower thrips populations jumped when peppers began to bloom, but so did the numbers of predatory minute pirate bugs, Frantz says.
Eastern flower thrips and Florida flower thrips are native species that pose a far smaller threat than Western flower thrips, he says. They do less damage, are poor disease vectors and are less likely to develop pesticide resistance, making them easier to kill.
As an introduced species, Western flower thrips flourish on cultivated crops but are forced to "duke it out" with their native cousins on weeds and other native plants. There, Florida flower thrips "can flood the environment," he says.
The native thrips outcompete Western flower thrips.
Encouraging Florida flower thrips means growers trade "the risk of a little bit of damage versus the bigger problems of Western flower thrips," Frantz says.
In the second year of Surround treatments, the predator-prey ratio hit the critical level for pest suppression and extinction a week earlier than in the control plots, Frantz says. One predator for every 180 thrips is considered enough for suppression, while increasing the numbers to one predator per 40 thrips achieves control.
The underlying is unclear, Tyler-Julian says.
Theories include an irritant effect, uncomfortable levels of light from the kaolin's reflective qualities, the pest's problems with gripping the plant and laying eggs through the additional material—or a combination of these.
Kaolin sprays may be a harder sell for pepper and tomato growers than other pieces of the push-pull strategy, Frantz says.
The whitish residue must be washed off fruit after harvest.
But because benefits appear within two weeks of use, growers may be able to reduce the amount and number of sprays over the season, simplifying cleanup, he says.
A trap-crop border
Meanwhile, planting alternate host plants on the edges of field rows reduced the number of thrips on pepper and tomato plants, Tyler-Julian says. Those tests found a correspondingly lower incidence of tomato spotted wilt virus.
Infected Western flower thrips transmit the virus while feeding on plants as adults. Laying eggs on infected plants passes the disease to a new generation that acquires it as larvae to spread tomato spotted wilt virus in its turn.
Keeping infected adults away from vulnerable crops stops that chain from continuing.
Parts of the state, including Palm Beach County, have low populations of minute pirate bugs.
"Farms are too clean," Funderburk says. "There's not enough wild vegetation" to attract beneficials or to serve as traps for Western flower thrips.
That's where companion plantings of sunflowers for peppers and Spanish needle for tomatoes come in. But more work is needed to determine best practices as well as any additional benefits, he says.
One of those benefits seems to be in aphid control, says Gene McAvoy, a University of Florida regional vegetable Extension specialist in LaBelle.
But companion plantings reduce land available for crops, perhaps a greater concern on smaller acreages, Tyler-Julian says.
All these push-pull pieces together are crucial because growers can induce problems stemming from Western flower thrips, Funderburk. Pyrethroids can take out minute pirate bugs and other beneficials.
Danger also can come from efforts to control pepper weevil, another serious pest.
"The only control we have is pesticide that knocks hell out of the beneficials," McAvoy says.
Nightshade and other alternate hosts may offer a softer option for weevil control, he says. Researchers are looking into releasing beneficials in nightshade during summer months to knock down weevil populations.
"The point to remember is you're trying to grow a crop, not kill insects," Funderburk says.
Plants can sustain some insect injury before reaching a crop-damaging level.
"When you spray before you need to, you're creating damage," he says. "I've seen more damage from the overuse of pesticides than underuse."
Know which insects are in your fields, Frantz says. A thrips population may near threshold levels, but if it contains significant numbers of Florida flower thrips or is accompanied by an equally high number of predators, you may want to delay spraying.
"Let the beneficials do their job for you," he says.