"They've been a big disappointment for some farmers."

Paul Baumer, president of Cal-West Seeds, Woodland, CA, is referring to potato leafhopper-resistant alfalfa varieties, which were introduced for the first time last year.

Many growers were surprised to discover stunting and yellowing - common symptoms of leafhopper feeding - in their new stands. Some applied an insecticide to prevent further damage.

Unusually heavy leafhopper infestations over a wide area, coupled with lower-than-expected resistance levels in the new varieties, are blamed for the problem.

Several seed companies introduced first-generation leafhopper-resistant varieties in 1997. The varieties have tiny glandular hairs on their stems and leaves that fend off leafhoppers.

In an effort to get the new technology to the marketplace quickly, not all companies tested the varieties under the severe conditions that growers saw in '97, says Clive Holland, Pioneer's product manager.

"As a company, we were surprised by the severity of the leafhopper infestations and the necessity of spraying," he adds.

"Growers' expectations were raised above where they should have been with these first releases," says Mark Sulc, Ohio State University extension forage specialist.

"Some marketing of the new varieties gave the impression that it wouldn't be necessary to spray," says Sulc. "But our research data clearly shows that it pays to spray in the seeding year when leafhopper populations are heavy."

Because the seed costs up to 35% more than seed of conventional varieties, growers expected more, adds Sulc.

"They figured that, if they paid around $5 per pound for seed, they wouldn't have to get their sprayers out," says Cal-West's Baumer, who also heads the Certified Alfalfa Seed Council.

"Growers who thought they were buying a product with 100% insect resistance have been disappointed," concurs Holland.

Descriptions of pest resistance for Bt corn and Roundup Ready soybeans, introduced at about the same time as leafhopper-resistant varieties, helped build similar expectations for the new alfalfas, he says.

Unlike a corn hybrid, an alfalfa variety is a population of plants characterized by percent expression of different traits.

"No alfalfa variety is 100% resistant to any disease or pest, including leafhoppers," he states.

The varieties qualify as resistant under an industry system that rates varieties based on percentage of plants resistant to a particular pest. In that system, varieties with 16-30% resistant plants are called moderately resistant. Varieties are resistant if 31-50% of the plants are resistant; highly resistant if more than half fend off the pest.

According to Sulc, most leafhopper-resistant varieties introduced last year have, at best, 35% resistant plants. That resistance level, combined with record leafhopper numbers, gave the new varieties a rigorous workout in their first year.

University extension agents reported that '97 leafhopper infestations reached a 10-year high in several states, with pressures three to five times above normal. In Ohio, leafhopper numbers exceeded economic threshold levels by 15 or more times in some fields, reports Sulc. The pests spread to many areas, including western Nebraska and Kansas, where they're rarely seen.

Resistant varieties were especially vulnerable because they were all in new stands. First-year stands are more prone to leafhopper damage than established fields, because the plants are more tender and grow slower, says Sulc.

For growers who don't regularly scout and spray for leafhoppers, resistant varieties are a significant improvement, says Sulc.

"If growers don't spray on a timely basis, there's no question that the resistant varieties are going to be more profitable and pay for themselves in the first year when leafhopper pressure is high," he states.

In a six-location study by Mark McCaslin, an alfalfa breeder with Forage Genetics, West Salem, WI, established stands of resistant varieties outyielded susceptible varieties by 10-25%.

Although current leafhopper-resistant varieties may benefit from seeding-year spraying when insect pressure is high, that might change as varieties with higher resistance levels are developed. Plant breeders are busy developing varieties with up to 70% resistant plants.

"Five years from now, there will be a whole new set of potato leafhopper-resistant varieties on the market, and all of them are going to have much higher levels of resistance," says McCaslin.