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Reducing Damage from Potato Leafhoppers on Alfalfa in New York through Variety Selection: A Comparison of Resistant vs. Susceptible Varieties 1998

Project Leaders: Julie Hansen, Jill Miller-Garvin, J. Keith Waldron, Don Viands

Objectives:

1. Compare potato leafhopper-resistant and susceptible alfalfa varieties for potato leafhopper (PLH) damage and yield in the first production year and winter survival following a seeding year season with heavy insect pressure at one location and moderate insect pressure at a second location.

2. Compare PLH-resistant and susceptible alfalfa varieties for forage quality and nymph counts at two harvests/locations where PLH damage is greatest.

Results:

Sweep data in 1998 at the site with moderate insect pressure in the seeding year (Clarendon) indicated that the PLH population was above threshold only at the second harvest on July 22. Yields of resistant varieties were significantly lower than those of susceptible varieties when PLH was below threshold. When PLH was above threshold, average second-harvest yields were equivalent for susceptible and resistant varieties.

At the site that had heavy insect pressure in the seeding year (Ithaca), sweep data in 1998 indicated that the PLH population was not above threshold at any of the nine sampling dates. However, first- and second-harvest yields of resistant varieties were significantly higher than those of susceptible varieties. Second-harvest PLH damage scores and PLH nymph and adult counts were significantly lower on resistant varieties than on susceptible ones. The yield advantage of the resistant varieties may be due to carryover effects from seeding year damage, since PLH was below threshold in 1998.

Resistant varieties had higher protein concentration at both locations. The value per acre was higher ($19/A) for resistant varieties than susceptible varieties at Ithaca, and was lower (-$6/A) for resistant varieties at Clarendon.