The near-record warm winter Ohio experienced this year has not only caused alfalfa to an earlier first cutting than usual, it's also caused some insects to appear earlier than normal. One example is the potato leafhopper, which has already been reported in alfalfa fields by some growers across the state, an Ohio State University Extension entomologist said.
As a result, growers should begin scouting for the leafhopper when alfalfa regrowth reaches sufficient height for sweep-net sampling, says Ron Hammond, who also has an appointment with the Ohio Agricultural Research and Development Center.
The problem is that the potato leafhopper, which migrates to northern states from Gulf Coast states, can cause significant loss to alfalfa growers, he says.
"We're already getting reports of fields having to be to be treated for potato leafhoppers, causing growers a significant economic impact," Hammond says. "These pests can result in stunted alfalfa plants or yellow plants, which is caused by leafhopper burn.
"That results in the yellowing of the leaves and could cause significant yield loss and impact the plant's nutritional value."
The insects are being seen earlier in Ohio this year because of the warm winter and early spring experienced in the region over the past several months, which has resulted in alfalfa maturing at least two weeks earlier this year, he says.
"Everything is early this year," Hammond says. "The first cutting or harvesting has already occurred a few weeks earlier.
"The alfalfa just grew a lot quicker to begin with. We usually wouldn't see the first cutting for a few more weeks. And normally we'd see these pests more in the mid- to later part of June."
But growers can control the pests, he says.
"This is definitely one of our best examples of good Integrated Pest Management," Hammond says. "We have really good thresholds for them."
Growers should start by scouting and sampling their fields, he says.
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, Hammond says.
"For example, if the alfalfa is 6 inches tall and the average number of leafhoppers is six or higher, insecticide treatment is warranted," he says. "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. In that case, the threshold would be 18 leafhoppers for 6-inch tall alfalfa, Hammond says.
"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," he says. "After the first cutting, growers can then use three times the normal level threshold."