The potato leafhopper (PLH) is usually
the most damaging insect pest of alfalfa in Ohio. Beginning in 1997, commercial
varieties with improved resistance to this pest have been sold. The largest
gains in resistance have been achieved using germplasm with erect glandular
hairs on the stems and leaves. These varieties show resistance through reduced
survival of adults and nymphs feeding on the foliage, and by reduced egg laying
and feeding preference of adults.
Tables 8 - 9 summarize results from trials
seeded at S. Charleston in 2001 and 2002, to evaluate performance of the new
glandular-haired alfalfa varieties. PLH-resistant varieties had higher yields
than susceptible entries (5454, Vernal, 54V54) because populations were very
high.
Seeding year alfalfa is very
susceptible to PLH. Although the glandular-hair resistance trait can
dramatically reduce this damage, yield reductions still occur in the resistant
varieties when PLH infestations are high. Based on our observations and data
collected to date, we recommend that PLH resistant varieties be carefully
scouted during the establishment year, and insecticide applied if PLH
populations exceed the normal action threshold, especially during the very first
growth cycle. In established stands, insecticide treatment may also be warranted
if PLH populations are very high (especially if populations approach three times
the normal threshold). PLH-resistant varieties are not resistant to alfalfa
weevil, and will need to be treated with insecticides when weevil populations
exceed action thresholds. No insecticide was required to control alfalfa weevil
in Spring 2003 due to the very low weevil populations.
For more information on potato
leafhopper management and control, see Ohio State University Extension Fact
Sheet FC-ENT-31 (Insect Pest Management on Alfalfa) and FC-ENT-33 (Potato
Leafhopper on Alfalfa). These are available through county Ohio State University
Extension offices or through Ohioline on the Internet at (https://ohioline.osu.edu).