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).