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June 1, 2001

White-washing melons
may change pest control

By Rod Santa Ana III
Extension Communications Specialist

Snow-covered fields of Rio Grande Valley vegetable, cotton and citrus trees could soon be a reality there. But it's not the weather that's changing; what could soon change is the way local growers protect their crops from profit-robbing insects and plant diseases.

A relatively new and cheaper method of managing insect pests is being tested on South Texas crops that involves spraying a white coating on plants that repels insects and diseases. The method is called particle film technology, and it leaves plants looking as if a light snow has fallen. It's been used successfully for a few years on fruit trees in the north, and the same technology has shown excellent results on Valley crops.

Dr. T-X Liu, a vegetable IPM entomologist at the Texas A&M Agricultural Research and Extension Center at Weslaco, and GeMei Liang, a doctoral student from China, recently concluded experiments on melons, the first time this method has been tested on vegetables. Results in the laboratory were so promising, field tests are planned on melons and other crops.

"It's amazing how well this new process works against whiteflies on melons," said Liu. "I think it has great potential for other Valley insects and crops, including leafminers and weevils on peppers, thrips on onions, the cotton boll weevil and on citrus pests like mites and even the diaprepes root weevil, which lay eggs on leaves. Florida has reported very good results in controlling diaprepes. Pathogens like fungi are also repelled because they can't penetrate the coating."

Particle film technology was developed by two USDA scientists in West Virginia, Michael Glenn and Gary Puterka. It involves mixing a specially formulated white clay material, kaolin, with water that is then sprayed on plant leaf surfaces with conventional sprayers. After water evaporates, it leaves a milky white coating on plants. The material's brand name is Surround and is manufactured by the Englehard Corporation of New Jersey.

Kaolin (pronounced KAY-eh-lin) is an inert mineral used in the production of porcelain and other construction materials. It is non-toxic and is even approved by the Food and Drug Administration as an indirect food additive. It doesn't affect crop pollination and doesn't harm beneficial insects.

"What it does, when you spray it on a plant leaf, is that it confuses and repels insects," said Liu. "It doesn't inhibit photosynthesis in any way. In fact, it helps the process by evenly distributing the light source. And that helps fruit get a more uniform color. In the summer it cools off the plant and in the cooler temperatures of early spring or fall, it warms the plant."

Liu said whiteflies are attracted to green and yellow colors. If they land on a green or yellow car, for example, their ability to smell and probe with a snout tells them to continue looking for a plant on which to feed and reproduce.

"When a whitefly lands in a crop field sprayed with this kaolin," Liu said, "the whitefly doesn't like it. They get disoriented when the material gets on their bodies and they continue flying. But tests show we may not want to spray an entire field because eventually they'll get tired and hungry enough to feed on a kaolin-coated plant, even if they don't like it."

Liu said it's a better idea to leave rows of unsprayed plants where whiteflies will gather and where they can be treated with insecticide.

"What we have to determine in the field, among other things, is how to apply it to both sides of leaves and determine how many rows we should leave unprotected. Should we leave one in three rows unprotected, one in five, what is the optimal rate? We don't know that yet," he said. "Timing of sprays and application rates will also be evaluated."

Thanks to adhesive agents in the mix, high Valley winds shouldn't be a problem for kaolin sprays. But rain is. "It washes right off with water," said Liu, "so this method is especially good for crops that are washed off in the post-harvest process anyway. This product is much cheaper than insecticides, and we could drastically reduce the amounts of insecticides we currently use."