Thrips Gone Wild

01/01/2010 02:00:00 AM
Vicky Boyd, Editor

What has been a decades-old problem in northern Florida peppers, tomatoes and eggplants—Western flower thrips—has recently become a pest in the southern part of the state.

Many of the same lessons learned in the north, such as adhering to strict integrated pest management tactics and preserving beneficial insects, can be applied to the south, says Joe Funderburk, a University of Florida entomology professor.

“We have to quit making recommendations for just one pest,” says Funderburk, who’s based at the Institute of Agriculture and Food Sciences North Florida Research and Education Center in Quincy.

In addition, he says, pest management decisions need to be vertically integrated. The situation in the south is complicated by pockets of Western flower thrips that have grown resistant to the spinosyn class of insecticides, which includes Radiant, Success, SpinTor, Entrust and Naturalyte. These belong to the Insecticide Resistance Action Committee’s Group 5.

Dow AgroSciences, the products’ manufacturer, has taken the drastic step of requesting that the Environmental Protection Agency issue a Section 24 (c) special local needs registration in Broward and parts of Palm Beach counties. The SLN registration prohibits spinosyn use until May, at which time it will be reviewed, says Tony Weiss, Dow product technology specialist based in Brandon.

“When you look at Western flower thrips, the only effective product that was available was Radiant, so that kind of tells the story,” Weiss says. “I think over time, we’ve learned more about how to manage Western flower thrips and understand the thresholds and understand the importance of identification and finding other ways to manage it rather than just with pesticides.”

Even without this highly effective class of chemistry, growers and consultants can still manage Western flower thrips with an IPM program, says Charlie Mellinger, a certified professional crop consultant and technical director of Jupiter-based Glades Crop Care Inc.

“Joe called it vertical integration—I always thought of it as a systems approach,” Mellinger says.

A one, two punch

Western flower thrips cause damage on two fronts. The adults and immatures, or nymphs, feed on the epidermal cells of fruit, causing damage known as flecking. Adult egg-laying on tomatoes causes dimpling or halo spots.

The adults also can spread tomato spotted wilt virus, which some consider to be the most serious viral diseases of tomatoes and peppers worldwide.

Western flower thrips and the virus have a unique relationship, Funderburk says. Only the nymphs can pick up the viral disease when feeding on infected plants.

The virus remains in the insect until it reaches adulthood, at which time the adults can spread it to healthy plants.

Western flower thrips head south

Western flower thrips were first confirmed in the state in 1985 in the northern production areas.

Growers have always seen the native Eastern flower thrips and Florida flower thrips, but they typically don’t cause economic damage, Funderburk says. In addition, they tend to outcompete the Western flower thrips under natural circumstances.

When the competition and beneficial insects were removed by broad-spectrum pesticides, Western flower thrips took over.

“The worst thing that can happen to pepper growers is when a [pepper] weevil problem comes in,” says Madeline Mellinger, president and founder of Glades Crop Care. “Once you nuke the weevil, you kill the Florida thrips and you open yourself up to the damaging thrips.”

Meanwhile, in the southern part of the state, Western flower thrips didn’t appear until 2005.

Funderburk and UF colleagues have developed an IPM program for peppers and eggplant that relies heavily on preserving the minute pirate bug, a voracious enemy of Western flower thrips. A thrips management plan for tomatoes is in the works.

Photo by Frank Peairs, Colorado State University; Bugwood.org
When battling Western flower thrips, take an integrated approach and choose pesticides that preserve beneficial insects, such as the minute pirate bug (above). And make sure they don’t flare Western flower thrips (above right).
Photo courtesy of the Agricultural Research Service

ID, thresholds and beneficials

Key to the programs is identifying thrips species when scouting, Funderburk says.

If you’re growing peppers in the north, the treatment thresholds are six Western flower thrips per flower or two larvae per fruit.

One minute pirate bug can consume up to 100 thrips. That means that one Orius spp.—as the group is known scientifically—per 50 Western flower thrips can keep the pest under control without spraying.

“If you’re up in Quincy, it’s a whole different scenario than in southeast or southwest Florida,” Charlie Mellinger says. “If you’re dealing with Western flower thrips with tomato spotted wilt virus present, then the threshold is much lower because you can’t tolerate a few thrips.

“But if you’re in south Florida or even on the East Coast where we don’t have much TSWV, the Western flower thrips threshold can be much higher than in Georgia or north Florida.”

If Western flower thrips exceed the threshold, carefully choose an insecticide that will preserve the beneficials, Funderburk says.

Fenpropathrin (Danitol) and pyrethroids kill the predators as well as the native thrips, leaving Western flower thrips alone to go wild.

Learning about new products

The spinosyns have been the main products of choice because they are effective against Western flower thrips yet soft on minute pirate bugs, Weiss says.

Registration of a handful of soft insecticides that are effective against thrips is on the horizon, Funderburk says.

Although the new products should relieve some of the resistance pressure, they could cause resistance problems if not used carefully, he says. When they’re registered, the newcomers should not be viewed as stand-alone controls and should be incorporated into an IPM program.

Researchers also are learning how to use already registered products more effectively against Western flower thrips.

For example, Requiem, a biological insecticide derived from a plant extract by Davis, Calif.-based AgraQuest, is relatively ineffective against thrips when applied just once, Funderburk says. But follow the initial application five to seven days later with another application of Requiem, and thrips control improves significantly.

Going vertical to fight Western flower thrips

Below are highlights of the integrated pest management plan for Western flower thrips in peppers and eggplant developed by Joe Funderburk, a University of Florida professor of entomology and nematology, and a group of colleagues.

In scouting programs, distinguish between adult and larval thrips, and identify adult thrips to species.

Economic thresholds: about 6 adult western flower thrips and melon thrips per flower, and about 2 thrips larvae per fruit.

Do not treat for adult Eastern flower thrips and Florida flower thrips as they outcompete western flower thrips.

When peppers are flowering, use insecticides for thrips and other pests that conserve minute pirate bugs.

Never use insecticides that induce Western flower thrips.

Use ultra-violet reflective mulches when forming beds.

Sunflower and other refugia provide a source for minute pirate bugs.

Vertically integrate management of Western flower thrips with other pests, including pepper weevil and Lepidoptera species.

Follow BMP’s (best management practices) for fertility and irrigation management.

To read the full recommendations, download the UF publication,

“Managing thrips in peppers and eggplant” at edis.ifas.ufl.edu/IN401.



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