Although a few weeks early this year, we are entering that time period when potato leafhoppers are being collected and thus, might become a concern in alfalfa.

Growers should begin scouting for the leafhopper when alfalfa regrowth reaches sufficient height for sweep-net sampling. A single sample is 10 sweeps of a sweep net.

When the average number of adults and nymphs in a sample is equal to or greater than the average height of the alfalfa stand, insecticide treatment is warranted. For example, if the alfalfa is six inches tall and the average number of leafhoppers is six or higher, insecticide treatment is warranted. If the average is lower, the grower should re-sample in a few days.

In glandular-haired, leafhopper-resistant alfalfa, the economic threshold is three times the normal threshold, or three leafhoppers per inch of growth (18 leafhoppers for six-inch tall alfalfa, for example). However, if the resistant alfalfa is a new planting this spring, growers might want to use thresholds meant for regular alfalfa during the very first growth from seeding.

After the first cutting, growers can then use three times times the normal level threshold. More information on potato leafhoppers, including how alfalfa growing conditions might affect the threshold, is available here.  FG

—Ohio State University C.O.R.N. newsletter, May 2012

PHOTO
Photo courtesy of Ohio State University.