Be Aware & Vigilant

08/01/2010 02:00:00 AM
Renee Stern

Florida growers and researchers are keeping a wary eye on chilli thrips, an invasive pest with potential to spread and damage a wide array of crops.

Florida’s landscape plant industry so far is ground zero for the pest since its discovery in the United States, but it’s been spotted as far away as Texas. Scattered Florida outbreaks also have occurred in blueberry, strawberry and pepper fields.

Around the world, chilli thrips attack crops ranging from cucumbers to tomatoes, mangoes, citrus and strawberries.

“It’s got the potential to go clear across the Sun Belt,” says Galen Frantz, senior crop management specialist with Glades Crop Care Inc. in Jupiter. “There’s enough traffic in foliage between Florida and California and all points in between.”

Rotate modes of action

Many transplant producers mingle ornamentals and vegetables, increasing movement opportunities, says Lance Osborne, entomology professor at the University of Florida’s Apopka research center.

Chilli thrips could spread even farther, says Dakshina Seal, assistant research scientist at the university’s Homestead research center. Based on its global range, crops as far north as Canada may be threatened.

But for now, growers have several insecticides, including neonicotinoids, available to keep chilli thrips in check.

Transplanted material seems to be the main source of new infestations. Vegetable growers’ practice of applying an initial insecticide spray immediately after putting in transplants appears to prevent chilli thrips from getting a foothold there.

But, Seal says, “It’s only a matter of time before they develop resistance and they will become a serious problem.”

A similar resistance pattern is showing up with melon thrips, which first appeared in Florida in the 1990s, he says.

Frigid weather last winter help cut chilli thrips’ Florida populations, but their rapid reproductive cycle means numbers rebound when temperatures rise, Osborne says. “They’re just not starting at the levels of previous years.”

A new generation every two weeks during summer makes scouting crucial, says Scott Ludwig, integrated pest management specialist Texas AgriLife Extension Service in Overton. Without immediate attention, pest populations may shoot out of control.

Chilli thrips feed on tender new growth, primarily foliage, often sheltering in the centers of plants where that growth is concentrated. Outer layers can make them hard to spot.

“Anything that grows and is flushing in June and the rest of the summer months is at risk,” Ludwig says.

“New growth (eventually) becomes old growth,” says Jim Price, entomologist at the University of Florida’s Wimauma research center.

Over time, the damage hinders plant growth and production.

Identify pest, then treat

In strawberries that damage—a black streaking on leaves—is obvious at a glance, Price says.

In other plants damage may show up either as undersized leaves or leaves that are crinkled with brown streaks, Ludwig says.

But other thrips as well as broad mites produce similar effects, Seal says. Growers always should pinpoint which problem pests are in their fields in order to devise the most effective control program.

Chilli thrips are whitish, with a small band on their abdomen, and are smaller than either melon or western flower thrips, he says.

So far, Price has found chilli thrips only in isolated spots on commercial farms, mainly on strawberry field margins, where the pest has migrated in from nearby landscaping plants—unlike western flower thrips, which typically blow in and cover fields more uniformly.

“Be aware of your vulnerability to the problem,” he says. “If you’re near residences with landscape plants, scout accordingly.”

Consider treatments’ effects on other insects, too

Shrub roses, a popular landscaping plant with a growing season that runs from spring to fall, are a particular concern, Ludwig says.

Neighboring nurseries can pose similar threats, Seal says. And consider quarantining transplants to be sure they’re pest-free before setting them out in fields.

After scouting fields, growers should follow recommended spray plans and rotate pesticide classes to manage resistance.

And, Osborne says, keep the big picture in mind. Going overboard on sprays against chilli thrips may lead to a more dangerous problem with western flower thrips, which vector tomato spotted wilt virus and other diseases.

“We don’t want to create a resistance problem in western flower thrips,” he says.

“Growers can make their own problems,” Frantz says. “There are some pesticide use patterns that can trigger [pest] population increases.”

Frequent pyrethroid sprays are a prime example, he says. Pyrethroids wreak havoc on thrips’ predators and other beneficial insects. The end result can be a population explosion in western flower thrips.

In addition to neonicotinoids as a foliar spray, the researchers suggest other traditional thrips’ controls, including abamectin (marketed as Agri-Mek, among other brands) and spinosads, such as Radiant.

Biological controls also play a role. Osborne cites one study that’s demonstrated the benefits of predatory mites to manage the pest.

Other thrips’ predators, such as minute pirate bugs, also should prove their worth against chilli thrips, Price says.

Judicious use of insecticides can help strengthen populations of native Florida flower thrips, whose competing presence may lock out pest thrips, Frantz says.

In the end, he says, the best defense is to “be aware and be vigilant.”

Contact Citrus + Vegetable Magazine at vlboyd@att.net or (209) 571-0414.



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