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 9 - 12 summarize results from trials seeded at S. Charleston, and Wooster, to evaluate performance of the new glandular-haired alfalfa varieties. First harvest yields were reduced in those trials by alfalfa weevil damage (no insecticide was applied to control infestations in 2001 at South Charleston). All varieties suffered damage by the alfalfa weevil. The results demonstrate that the PLH-resistant varieties are not resistant to alfalfa weevil, and will need to be treated with insecticides when weevil populations exceed action thresholds. The weevil damage in those trials contributed to the lower overall yield for the 2001 season, compared with the standard insecticide-treated trials. All trials were sprayed to protect against alfalfa weevil infestations in 2002.
Yield differences among the susceptible check variety (5454 a standard, non-glandular-haired variety) and glandular-haired varieties were relatively small this season in trials seeded before 2000 (Table 9). In contrast, the PLH-resistant varieties had higher yields than susceptible entries (5454, Vernal, 54V54) in the 2000, 2001 and 2002 seeded trials at S. Charleston (Tables 10-12), where PLH 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 twice the normal threshold).
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).