If potato leafhoppers threaten to limit alfalfa yields, perhaps it's time to take a closer look at resistant varieties. New alfalfa varieties are incorporating significantly higher levels of leafhopper resistance than a few years ago.
Those early resistant varieties were plagued by unacceptable yield drag: Unless leafhopper pressure was considerable, growers felt they were sacrificing too much potential yield.
Not anymore. “The latest generation of resistant varieties offers good resistance without obvious yield drag,” says Dan Undersander, University of Wisconsin Extension forage agronomist.
“Yields of the newest leafhopper-resistant varieties are similar to yields of susceptible varieties, even when there's little or no leafhopper pressure,” agrees Mark Sulc, associate professor in the Department of Horticulture and Crop Science at The Ohio State University.
Testing yield levels
When high populations of leafhoppers threaten alfalfa stands, the value of resistance is obvious. Sulc conducted studies in 2005, 2006 and 2007, evaluating alfalfa stands in South Charleston, Ohio, and Ames, Iowa. Leafhopper populations generally were very high at the Ohio site and low in Iowa.
The conclusion: Resistant varieties showed significant yield advantages over susceptible varieties because of less leafhopper injury.
“The most underused trait of some alfalfa varieties is potato leafhopper resistance,” Undersander says. He notes today's higherresistance varieties yield more than 40 percent higher than susceptible lines.
In fact, the best variety in Sulc's 2006-07 study, Pioneer® variety 53H92, posted a 50 percent increase above susceptible check lines in the seeding year and averaged 45 percent higher over two years. In another trial at Michigan State University, 53H92 yielded 48 percent higher than the check varieties over two years.
“These trials show growers should consider leafhopperresistant varieties if they face potato leafhopper pressure,” Sulc says. “Resistant varieties provide protection against this insect, offer a risk management tool and deliver a convenient management solution for growers.”
Resistant varieties limit the need to scout so diligently for leafhopper infestations and make spraying decisions. And you won't have to handle insecticides. When you rely on spray insecticides, you're at the mercy of the weather for timely application.
Limit your losses
Although heavy leafhopper pressure will curb yields even for resistant varieties, Sulc says losses will be less damaging.
“When leafhopper pressure was high, resistant varieties showed a 0.14 ton-per-acre yield advantage when sprayed for leafhoppers over unsprayed,” Sulc reports. “That's borderline for making spraying worthwhile.”
Susceptible varieties yielded 0.4 ton-per-acre yield more when sprayed compared to those not sprayed. “Yield losses with resistant varieties may be about one-third of those you might see with susceptible varieties.”
Potato leafhoppers migrate north each spring. Given the right conditions, they flourish through the summer, producing several generations of offspring to feed on alfalfa leaves.
“Resistant varieties don't allow as much reproduction of leafhoppers as susceptible varieties,” Sulc notes. “Also, their feeding isn't as constant. They tend to move around trying to find better feeding sites.”
Resistant varieties can help maintain yields when leafhoppers pounce upon your fields.