PRODUCTIVITY AND PERSISTENCE OF DECLINING ALFALFA STANDS AS INFLUENCED BY THE ALFALFA WEEVIL, WEEDS, AND EARLY FIRST HARVEST IN OKLAHOMA

Abstract

AbstractImportance of cultivars, harvest schedules, and pest infestations as determinants of alfalfa, Medicago sativa L., productivity and stand persistence was investigated using the unimproved “OK08” (Oklahoma Common) and the multiple-pest resistant “WL 318” cultivars. Beginning in the 5th year of production, treatments including three first-harvest schedules (early bud, early bloom, and full bloom) were imposed in a factorial arrangement with unsprayed subplots and three pesticide options for control of alfalfa weevil, Hypera postica (Gyllenhal), or weeds such as downy brome, Bromus tectorum L., or both. In addition to estimating population levels of alfalfa weevil and percentage composition of weeds in forage during each year, alfalfa dry matter yield and stem densities (no. per square metre) were determined during the 3-year period from 1986 through 1988. The seasonal forage production (2-year mean) of WL 318 was nearly 5.4 Mg per hectare greater than that of OK08. There was no consistent trend for greater seasonal alfalfa yield with any of the first-harvest schedules. Timely application of pesticides, as well as use of the improved cultivar were essential for maintaining productivity in years 5 through 7 of stand life. At the termination of the study, only the herbicide + insecticide treatment of WL 318 had close to sufficient stem (and plant) numbers remaining for continued production.