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Agronomics and Economics of Potato Leafhopper (PLH)-resistant Alfalfa Intercropped with Perennial Forage Grass for PLH Control 2006

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Project Leaders: J. Hansen, Research Associate, Plant Breeding and Genetics, Cornell University; J.K. Waldron, Senior Extension Associate, IPM Coordinator, Cornell University; J. Losey, Professor of Entomology, Cornell University; D. Viands, Professor of Plant Breeding and Genetics, Cornell University ; J. Hanchar, Extension Associate, Cornell University

Cooperator: J. Cherney, Professor, Cornell University

Abstract: Potato leafhopper (PLH) is the most damaging alfalfa pest in the Northeast (NE). Forage grasses mixed with alfalfa can cause PLH to emigrate but may reduce forage quality. Some alfalfa cultivars have PLH-resistance, yet are not immune to PLH damage. The objectives are to compare PLH populations and densities, and forage yield and quality of a conventional alfalfa cultivar and a PLH-resistant cultivar both in monoculture and intercropped with grass, to conduct an economic analysis, and to share results in extension outreach. For conventional alfalfa not sprayed with insecticide, the alfalfa : grass mixture plots compared to the monoculture alfalfa plots averaged significantly lower PLH damage scores (2.7 vs. 3.2), lower number of PLH insects in 5 sweeps (19.4 vs. 30.0), and higher total season yield (2.11 t/a vs. 1.88 t/a (P<0.0677)). For PLH-resistant alfalfa, planting with a grass did not significantly reduce PLH damage and populations more than was achieved by using a PLH-resistant alfalfa cultivar. Even though the PLH-resistant alfalfa cultivars stayed green when some PLH were observed, the cultivars were still significantly stunted from this feeding damage compared to alfalfa that was treated with insecticide.