April 8, 2005

Photos and Graphics Click for larger images

WESLACO – The citrus rust mite is so small that it can't be seen by the naked eye. But for Rio Grande Valley citrus growers, the tiny critter is a savage monster that gobbles up untold millions in lost profits.

That's why growers here are so anxious to get their hands on a promising new chemical miticide, Envidor, which should be on the market soon.

"The citrus rust mite was the Valley's worst citrus pest in 1950, and it remains at the top of the list of pests today," said Dr. Victor French. French is an entomologist at the Texas A&M-Kingsville Citrus Center at Weslaco who has been testing Envidor since 1997.

French said the citrus rust mite can reproduce rapidly, with a generation lasting only seven to 10 days. Left unchecked, the populations explode, feeding on the leaves and fruit of orange and grapefruit trees. That debilitates the trees and makes fruit unappealing to consumers.

No dollar figures for the damage caused by citrus rust mites are available. But the toll in South Texas is so high and populations so difficult to control, French nicknamed the pest "mighty mite."

"These pests do not affect the internal quality of the fruit," French said. "But when they stick their feeding appendage into the fruit, they inject a toxin that causes a very obvious brown stain or blemish to develop on the fruit peel, called "russeting." If populations are not controlled early in the season, a heavy infestation can also result in small fruit. The fruit never sizes up."

Since consumers shun small, blemished grapefruit and oranges, an affected crop is relegated to juice and growers are paid a fraction of what they make in fresh market sales.

"Our growers take a real beating, financially, when that happens," French said. "Florida citrus is grown primarily for its juice, so after their fruit sizes up they are not too concerned with fruit blemish. But Texas citrus is produced for fresh market, so it's important to treat for citrus mites throughout the season, which can be an expensive proposition."

The citrus rust mite has developed resistance to some of the existing miticides, often making treatments a futile proposition for many growers. Envidor, developed by Bayer CropScience, is made with a new and different chemistry that French said is highly effective against all life stages of the mite, including the egg stage.

"That's important because it can nip the problem in the bud," French said. "But like all miticides, Envidor has to be applied properly, with air-blast sprayers so coverage penetrates the tree's canopy. You can have the best compound in the world, but if it doesn't reach the pest, it's worthless."

Will Envidor knock the citrus rust mite from atop its perch as the No.1 citrus pest of Rio Grande Valley citrus? French doesn't think so. He said the mites is so small, populations often go undetected by growers until it's too late.

"It takes a trained eye to spot them, and if they're not detected and treated early, they become established, and control with any product is difficult because they reproduce so rapidly. But having a new and effective weapon in our arsenal against these pests can only help," he said.

Company representatives say Envidor is in the final stages of registration by the federal government and should be on the market within weeks.