OSU Expert: Growers Should Begin Scouting for Potato Leafhopper in Alfalfa Earlier This Year
WOOSTER, Ohio – 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, said 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 said.
“We’re already getting reports of fields
having to be to be treated for potato leafhoppers, causing growers a significant
economic impact,” Hammond said. “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
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 said.
“Everything is early this year,” Hammond
said. “The first cutting or harvesting has already occurred a few weeks
“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
“This is definitely one of our best
examples of good Integrated Pest Management,” Hammond said. “We have really
good thresholds for them.”
Growers should start by scouting and
sampling their fields, he said.
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 said.
“For example, if the alfalfa is 6 inches
tall and the average number of leafhoppers is six or higher, insecticide
treatment is warranted,” he said. “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,
“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 said. “After the first cutting, growers can then use three
times the normal level threshold.”
More information on potato leafhopper, including how alfalfa growing
conditions might affect the threshold, can be downloaded at http://ohioline.osu.edu/ent-fact/pdf/0033.pdf