The potato leafhopper (PLH) is the most damaging insect pest of alfalfa in Ohio. Beginning in 1997, commercial varieties with improved resistance to this pest have become available. 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 10-14 summarize results from trials seeded at N. Baltimore, S. Charleston, Wooster, and Jackson to evaluate performance of the new glandular-haired alfalfa varieties. At N. Baltimore, PLH populations reached the economic action threshold only during the second harvest. Differences among the susceptible check variety (a standard, non-glandular-haired variety) and glandular-haired varieties were relatively small (Table 10). The susceptible check variety had good yields, demonstrating the low PLH pressure at that site. At S. Charleston, PLH populations were highest in the 1997 seeding and varieties differed in PLH injury, canopy height, and yield (Table 11). The PLH activity was low to moderate in the 1998 seeding at S. Charleston (Table 12), and low at Jackson (Table 13) and Wooster (Table 14). The results from all these trials demonstrate that plant breeders are continuing to make improvements in the glandular-haired varieties for leafhopper resistance, seedling vigor, and regrowth rate.
Seeding year alfalfa is very susceptible to PLH. Although the glandular-hair resistance trait dramatically reduces 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 high (especially if populations approach twice the normal threshold). Yield response to insecticide treatment in established stands will be greatest if PLH infestations reach high levels during the first 10 to 14 days of regrowth.
For more information on potato leafhopper management and control, see Ohio
State University Extension Bulletin 545, Insect Pests of Field Crops. It is
available through county Ohio State University Extension offices or through
Ohioline on the World Wide Web (www.ag.ohio-state.edu/~ohioline/).