Like fine wine that improves with age, potato leafhopper-resistant alfalfa varieties are getting a little better every year.
Alfalfa breeders have made "tremendous progress" in developing varieties with improved leafhopper resistance, says Mark McCaslin, a breeder with Forage Genetics, West Salem, WI.
"Levels of resistance in some of the third- and fourth-generation varieties are in the 70-80% range," says McCaslin.
When seed companies introduced the first leafhopper-resistant varieties in 1997, alfalfa growers welcomed the new technology. But many were disappointed when the varieties didn't provide high levels of control. Some, thinking they didn't need to scout and spray, suffered yield losses.
"The whole industry got a black eye when the first varieties were released because they didn't perform as anticipated," says Mike Velde, an alfalfa breeder with Dairyland Seeds at Clinton, WI. "Farmers are now very apprehensive of this technology, and it's going to take awhile to prove to them that it can work. I think this is the right way to go, but it's going to take a lot of research to provide enough resistance to control this insect."
In the first leafhopper-resistant alfalfas, only about 35% of the plants were actually resistant.
"We recognized that we needed to provide higher levels of resistance than were available on those first varieties," says McCaslin. "At 35% resistance, the varieties gave some protection, but not as much as most farmers needed - especially in a year with heavy leafhopper infestations."
One leafhopper-resistant variety being introduced this year is EverGreen from Novartis Seeds. Its resistance level is 79%, according to Dan Undersander, University of Wisconsin extension forage specialist. A few other new varieties boast resistances in the 50-55% range, he says.
In addition to improved resistance, the newest varieties are better-yielding, says McCaslin. In recent trials he conducted with and without leafhopper pressure, newer resistant varieties yielded just as well, or better than, susceptible varieties.
"With the early products, when leafhopper populations were above economic thresholds, they yielded significantly better than the standard varieties or checks," he says. "But in the absence of leafhopper damage, in most locations they yielded less than the checks."
That's because the leafhopper-resistant trait that researchers bred into new varieties had its origin in wild plant species, according to McCaslin. "Even though the wild relative provided resistance to the insect, it also provided a number of negative traits, such as lower yield, that had to be bred out."
He predicts that, "with the higher levels of resistance being introduced, the likelihood of having to spray will be greatly reduced."
But how can a grower find out if he's buying a variety that's more resistant than others?
"Some salespeople may not be able to tell you whether it's 65% resistant or 55%, but they should be able to tell you if it's classified as highly resistant, resistant, etc.," says McCaslin.
In highly resistant varieties, more than half of the plants are resistant. Varieties are resistant if 31-50% of the plants fend off the insects; moderately resistant if 16-30% are protected.
"Always ask the person who is selling you the variety for information about the level of resistance," McCaslin advises. "The more information you have, the better able you'll be to make a good decision."
Craig Sheaffer, University of Minnesota forage agronomist, saw only modest yield benefits in 1999 comparisons of potato leafhopper-resistant and susceptible varieties.
"We had very significant leafhopper populations in the state in 1999, with severe infestations and reinfestations throughout the summer," says Sheaffer. "Seasonal forage yields over three cuttings were reduced an average of about 7/10 ton/acre for the resistant varieties vs. 1 ton/acre for the check (susceptible) varieties. Some growers are concerned about a yield drag or reduction with resistant varieties, but we didn't see that."
Crude protein concentrations were decreased about five percentage points for both the resistant and susceptible varieties.
"I wish I had seen less reduction in crude protein and higher yields with the resistant varieties," says Sheaffer. "However, the resistant varieties we tested were established in 1998 and maybe the newer products will be better."
For growers who don't regularly scout and spray for leafhoppers, resistant varieties offer some benefits, says Sheaffer. But he's not ready to recommend them to everyone.
"It depends a lot on seed costs and the grower's overall management. If a grower is going to spray anyway, they're probably not going to be of great benefit."