South Carolina's No. 2 agricultural money-maker is under attack. Greenhouse growers are facing a new strain of whitefly this year - the Q-biotype sweet potato whitefly. The new strain may not be as susceptible to the usual insecticides applied in the past, said Clemson University agriculture researcher Dr. Richard Hassell.

The Q-biotype sweet potato whitefly has reached South Carolina, according to USDA researchers. The new whitefly was first detected in the United States in 2004, and now has been detected in at least 22 states.

The insect is a pest of many types of ornamental, vegetable and other horticultural crops. In 2004, the most recent year reported, horticulture, nursery and floriculture took in more than $295 million in South Carolina, second only to chicken broilers at more than $512 million.

This Q-biotype is similar to the B-biotype of the sweet potato whitefly (also called silver leaf whitefly). Both whiteflies cause crop damage by their feeding behavior and disease transmittal. They can reduce crop yields by sucking out plant nutrients and secreting a sticky substance that promotes the growth of fungus. Feeding by these whiteflies can cause plant disorders, including squash silver leaf, a silvering symptom on vegetables, and tomato irregular ripening, where tomatoes have both ripe areas and green/yellow portions. The pest also transmits several serious virus diseases of commercial crops.

In the field or in greenhouses, high infestations of whiteflies can be easily spotted by the presence of plant damage, immature whiteflies on the underside of foliage and adults that will readily fly when the plant is disturbed.

Shipping whitefly-infested plants, whether ornamentals or vegetable transplants, is one way exotic and native pests spread. Checking plants before and after shipment and rotating different insecticides against pest infestations may help manage this and other insect pests.

Yellow sticky cards can be used to supplement other monitoring tactics. If traditional controls fail to work, the whitefly population may have developed resistance to the chemicals, necessitating a change in management practice.

The identity of a biotype can be tested in a lab. Here's how:

• Collect a few adult whiteflies from several locations in the greenhouse.
• Place collected leaves between paper towels in a Ziploc bag.
• Place the sealed bag in the freezer to kill the insects.
• Contact the local Cooperative Extension agent for the address of the lab in South Carolina where the Q-biotype can be identified and for advice on control options.