The yield gap between potato leafhopper (PLH)-resistant alfalfas and standard varieties has been closed, says Marc Sulc, Ohio State University agronomist.

He compared a new PLH-resistant variety with a susceptible variety in studies funded in part by Pioneer Hi-Bred International. He made the comparison when no leafhoppers were present, and when leafhopper numbers were high and the standard variety was treated early or late with an insecticide.

“In both studies, yield performance was similar for both varieties when leafhoppers were not present or were controlled with timely insecticide applications,” Sulc reports. “When leafhoppers were present in high numbers, the unsprayed resistant variety yielded slightly less than the early insecticide-treated susceptible variety. But when the cost of insecticide treatment was added, there was a higher economic return for the unsprayed resistant variety.”

He found that the economic threshold for insecticide treatment on highly resistant varieties is three times higher than for susceptible varieties. Economic losses to resistant varieties occurred one-third as often as with susceptible alfalfa. Resistant varieties suffered only 30-40% as much yield loss as susceptible varieties when damage did occur.