Potato leafhopper-resistant versus susceptible alfalfa cultivars
in New York: A seeding year comparison of yield, quality,
and leafhopper feeding damage
J.E. Miller-Garvin, J.L. Hansen, J.K. Waldron, and D.R. Viands
Cornell University, Ithaca, NY 14850
Potato leafhopper (PLH), Empoasca fabae (Harris), is the most damaging insect
pest of alfalfa, Medicago sativa L., in the Northeast.
Economically-significant PLH populations may affect seeding year stand
survival and lead to reduced forage yield and quality in the following
production years. Risk from PLH can be expected annually; however, the
severity of infestations is variable from year to year and from county to
county. In 1997, seed companies introduced alfalfa cultivars purported to
have improved resistance to PLH. Resistant cultivars have the potential to
protect alfalfa from PLH injury, reduce insecticide use, and protect forage
quality, thereby enhancing net profitability. Our research objectives were
to: (1) compare PLH-resistant and PLH-susceptible alfalfa cultivars in the
seeding year for yield, PLH damage, and agronomic characteristics, and (2)
compare PLH-resistant versus PLH-susceptible cultivars for forage quality and
nymphal populations at one harvest/location where PLH damage is severe.
Field trials were established in western and central New York (Clarendon and
Ithaca, respectively) to increase the probability of encountering damaging
levels of PLH. Entries consisted of 19 cultivars, 8 with claims of some
level of PLH resistance, 8 susceptibles, and 3 of unknown resistance. Data
included yield, PLH damage (1-5 rating scale where 1 = no apparent injury and
5 = severe injury, McCaslin and Miller, 1996), nymphal counts per stem,
maturity, and quality. Forage quality data were entered into the FORVAL
program (Wilkens and Fick, 1988) and used to calculate dollar value per acre
per cultivar. Overall comparisons for yield and PLH damage score were
statistically significant at the Ithaca site, which had high PLH populations.
Resistant cultivars exhibited significantly higher yields and had lower PLH
damage scores. Forage quality and nymph sampling at Ithaca showed that the
resistant cultivars had fewer PLH nymphs per stem and had higher percent
crude protein and fiber (ADF and NDF), and were more mature. At the
Clarendon site, with moderate PLH populations, the resistant cultivars had
significantly lower PLH damage scores than the susceptible cultivars, but did
not differ significantly in yield. Ranking of the resistant cultivars for
PLH damage at both locations was similar. Based on NIRS analysis and FORVAL,
the resistant cultivars averaged $31.01 higher hay value per acre in the
seeding year than the susceptible cultivars at Ithaca. Although the extreme
level of PLH damage observed in the Northeast in 1997 is not expected on a
regular basis, the probability that at least one or more of the production
years/harvests of an alfalfa stand will be heavily damaged by PLH during the
life of the stand is high. In a year with severe PLH pressure, the
additional seed cost of resistant cultivars would likely be offset by
increased hay yields and quality, and reduced insecticide costs.
Reference
McCaslin, M. and D. Miller. 1996. Potato Leafhopper Resistance. In
Standard tests to characterize alfalfa cultivars. North American Alfalfa
Improvement Conference.
Wilkens, P.W. and G.W. Fick. 1988. FORVAL: A computer program using
chemical analyses and market data to price hay. J. Agron. Educ. 17: 122-127.
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