September 29, 2008

Chilli thrips attack Houston roses, landscape plants
Hurricane Ike could have spread the pest beyond the area

Writer(s): Robert Burns, 903-834-6191,rd-burns@tamu.edu

Contact(s): Dr. Scott Ludwig, 903-834-6191, swludwig@ag.tamu.edu

OVERTON – Chilli thrips, a new invasive insect pest, is causing severe damage to ornamental plants throughout the Houston area.

And Hurricane Ike may have spread the pest further, beyond the region, said Dr. Scott Ludwig, Texas AgriLife Extension Service entomologist and integrated pest management specialist.

The insect, only one-sixteenth inch long, is known to attack plants in at least 40 plant families, including many foundation plants in the landscape, Ludwig said.

"In Texas, ornamentals are the only plants they've been found on so far, but they have the potential to attack many other plants, including vegetables, blueberries, cotton and peanuts," he said. "The most common plants we've seen them on so far have been roses – all types, including types that were previously thought to be tolerant to pest problems."

Ludwig also has identified chilli thrips damaging cleyera, ornamental sweet potatoes and begonias in the Houston area.

Chilli thrips are usually detected in the landscape by the distinctive damage they do to plants while feeding. Chilli thrips "rasp" away developing plant tissue with their mouth parts, then suck juices from the wound. In response, leaves, buds and fruits may turn bronze in color, he said. Additionally, leaves may curl up and become distorted. Many infested plants become stunted and lose leaves or drop buds. The first finds of chilli thrips this year resulted from calls to the Houston Rose Society, Ludwig said. Landscape managers and homeowners wanted to know what was damaging their plants, and he was called in by the society to help diagnose the problem and provide management recommendations.

It's no surprise chilli thrips were detected in roses first. Roses are a very popular landscape plant in Texas, and many are highly susceptible to damage, he said.

For example, chilli thrips will cause severe damage to hybrid tea roses – if the roses haven't already been treated for flower thrips.

"We have seen chilli thrips basically kill all new growth in hybrid tea roses, so the plant is stopped in its tracks,” he said. “If there are flowers, they're highly disfigured."

In comparison, shrub roses may still continue to leaf out, but the leaves will be curled up and the number of flowers greatly diminished, Ludwig said.

Control of chilli thrips is not difficult but requires persistent treatment, Ludwig said. "Though the pest is easily killed with insecticides, we have not found any insecticides that provide long-term preventive control," he said. "Eliminating roses or planting something else may not be a solution since this pest has such a large host range."

To date, chilli thrips infestations have only been verified in Harris and Montgomery counties, Ludwig said.

"But with the pest being so small, hurricane-strength winds could have easily blown them farther north," he said. "Additionally, within the Houston area, during clean up, infested plant material may be moved into heretofore un-infested areas."

Whether the pest has been spread further won't be known for certain for at least a year, he said.

The more difficult issue is identification of the insect, as it is relatively new to Texas. In Florida, where the pest was discovered nearly four years ago, the damage caused by chilli thrips was at first confused with the effects of herbicides or foliar diseases.

"We have since seen the same issues in Texas," Ludwig said.

There are labeled chemicals that are effective in controlling the insect, but spraying must be done whenever plants have had a flush of new growth, he said.

Ludwig, who is one of the lead researchers of a national U.S. Department of Agriculture chilli thrips task force, currently is working to develop integrated pest management techniques specifically for the insect.

Integrated pest management, commonly known as IPM, strives to use less chemical pesticides by correct timing of applications, pest identification and biological controls.

So far in Texas, the pest has only been found to attack ornamental landscape plants. Those who think they may have an infestation may get help one of two ways, Ludwig said. They may visit a Web site that Ludwig maintains at http://chillithrips.tamu.edu or contact the AgriLife Extension office in their county. Contact information for county offices can be found at http://county-tx.tamu.edu/ . Ludwig’s Web site has contact information as well as pictures to help identify chilli thrips damage and ways to control the pest.

Ludwig emphasized that home gardeners should not start spraying just because they suspect they have chilli thrips.

"More often than not, indiscriminate spraying does more damage than good," he said. "Not only will they waste money and risk damaging their plants, they may kill the very beneficial insects that naturally help keep thrips in check."