Market prices have forever been the primary focal point for winter vegetable and melon growers and shippers in the desert growing regions of Southern California and Arizona.

A decade ago concerns about price were replaced by fears that there may not be crops to market because marauding, voracious clouds of the silverleaf whitefly (SLWF) were destroying crops at will. There was nothing pest control advisors could recommend to control them.

The small, sucking insects halted fall desert melon production in the early 90s because they were uncontrollable using foliar applications of existing products, and desert vegetable production was in serious jeopardy because of the millions of dollars in damage SLWF was causing, according to University of Arizona Research/Extension Entomologist John Palumbo stationed at the university's Yuma Valley Agricultural Center station.

Desperate for a solution, Palumbo, then a new addition to the UA staff, was asked to look at a new compound called Imidacloprid. That was 11 years ago and today the insect; the compound and the scientists are inseparably linked worldwide because the young scientist is considered a worldwide expert on controlling SLWF with the systemic insecticide.

The compound, which was first tried experimentally on vegetables in 1992, is named Admire (the soil applied formulation) and Provado (the topical formulation).

Validated effectiveness

Palumbo scientifically validated the compound as very effective against whitefly when applied to the soil just before or at planting or injected through drip irrigation system. It provides control for weeks.

Naturally, it was applied everywhere as soon as Section 18s and full labels were granted. Admire quickly became the industry standard for whitefly control not only in the desert, but also throughout the world, said Palumbo.

With such widespread use, the specter of insect resistant quickly began to surface. Some entomologists predicted Admire would be rendered ineffective by the mid 1990s because of resistance buildup to its widespread use. However, Imidacloprid remains as effective as ever, according to the entomologist. Palumbo has never recorded a commercial failure because of insect resistance, although the UA's insect resistance management lab has documented buildup in greenhouses.

Over the past eight years, Palumbo has documented a stable native SLWF population much smaller than the populations 10 years ago. And, during those eight years he has seen no decline in quality or yield on crops where Admire was applied correctly.

Palumbo told about 80 crop consultants at a recent Bayer vegetable consultants meeting in San Diego he believes there has been no commercial failures because of what he calls “defacto resistance management.”

He believes susceptible populations are maintained in crops like alfalfa where SLWF control is not necessary and in the urban landscape. This creates a population dynamics of susceptible whiteflies continuing to migrate into vegetable crops.

Also he said there is a wide diversity of spring, summer and winter crops grown in the desert and insect pests in them are controlled with other pesticides classes (parathyroid, organophosphates, carbamates). This is also precluding resistance buildup to Admire. He admitted, however, that producers have been “very fortunate” in this scenario.

Imidacloprid is so effective Palumbo warned the pest control advisors not to become too complacent in their use of the product.

He warned that even though populations have been low in recent years, there are more than sufficient SLWF populations remaining to cause problems, especially with viruses that can be vectored by the whitefly.

Delay as costly

“If you delay applications, you increase your chances for viruses,” he added.

Palumbo said the most effective incorporation depth for Admire is between 1.5 and three inches at planting or listing.

“Placement is the key to good efficacy,” he said, adding that it is the feeder roots of the young plants, which pick up the systemic insecticide. He recommends using the 16-ounce rate of the product.

“Sidedressing Admire has never been consistent in my trials,” he added.

Chemigation is the optimal; way to delivery Imidacloprid, he said. “It doesn't matter if it is subsurface or surface drip,” he added.