Managing Potato Leafhopper in Alfalfa
IPM tactics put to good use in year of heavy infestation
The 1997 growing season in New York was a remarkable year to be scouting alfalfa fields--remarkable because it was the worst potato leafhopper year in the northeast in many decades. Potato leafhopper (PLH) is the most damaging insect pest of alfalfa in New York and elsewhere in the northeast.
The best management practices for PLH have until recently been crop monitoring or scouting, early harvest when possible, and the use of insecticides when populations reach the economic threshold. Now growers have a new option to consider: PLH-resistant alfalfa varieties.
Evaluating Resistant Varieties. In 1997 several seed companies released commercial PLH-resistant or tolerant alfalfa varieties. They couldn't have timed it better. Cornell scientists Julie Hansen, Jill Miller-Garvin, Keith Waldron, and Don Viands compared 8 of these new varieties to 12 susceptible varieties in field trials at Ithaca and Clarendon. Sampling in the Ithaca fields (done by sweep-net catches) showed PLH presence above the economic threshold for 8 out of 12 sweeping dates between late June and mid-September.
The resistant varieties generally came out ahead of the susceptible ones by a significant margin on all counts under heavy insect pressure: higher yields, better feed value, higher net value per acre, and lower PLH damage. In spots where the insect pressure was only moderate, differences in yield were not noted. While these seeding-year results are encouraging, the "rest of the story" lies in how well the plants survive our New York winters and perform in subsequent years.
Training Pays Off. Growers who have gone through "TAg" training were at a distinct advantage when confronting the PLH infestation in 1997. A survey of New York alfalfa growers completed at the end of the growing season showed that TAg participants were much more likely than other growers to use sweep nets to determine PLH population levels and to hire scouts. They also remained vigilant for the PLH longer into the season, thus averting substantial losses sustained by some who ignored the problem after the second harvest.