Effects and Interactions of Early Season Pests on Alfalfa Yield in Kentucky

Abstract

A field study to partition effects and to examine interactions of three early season pests in two spring-seeded alfalfa stands was conducted from 1981 to 1984. The three pests, clover root curculio (CRC), Sitona hispidulus (F.); alfalfa weevil (A W), Hypera postica (Gyllenhal); and a complex of soil-borne root-rot fungi (FU), occur concurrently in Kentucky alfalfa fields. AW larval feeding, in years when population density exceeded the economic threshold, reduced alfalfa first-harvest yields. FU significantly reduced yields in four of five first harvests by ≤31.2%. CRC larval feeding directly reduced alfalfa yields in 1982 and 1984 by an average of 8.4%. Residual yield losses, associated with CRC larval feeding during April and May, also occurred in the second and third yearly alfalfa harvests. CRC lesions on alfalfa roots acted as colonization sites for FU. This apparently hastened development of root-rot diseases and resulted in a synergistic CRC and FU interaction in the second alfalfa harvests in 1982 and 1984. Stresses from both pests reduced alfalfa yield by 20.8% compared with ca. 8.0% losses from each pest alone. Significant partitioning of effects of the three early season pests was also found with alfalfa stem height, stem density, weed density in the herbage, and moisture content of alfalfa at harvest.