Date of Pod‐Set and Chalcid Fly Infestation in Alfalfa Seed Crops in the Southern Great Plains 1

Alfalfa ( Medicago sativa L .) is grown for hay and seed throughout the Southern Plains. Because of cropping practices and the extended reproduction period of the plant, seed pests are a serious problem in the region. Our objectives were to determine the level of alfalfa seed chalcid infestation by the approximate date of pod‐set, to estimate its effect on present crop yields, and to identify alternatives to current cropping practices. Alfalfa seed pods were classified into four color groups according to pod maturity and studied in seasonlocation combinations of one moist subhumid, two dry subhumid, and one semiarid environments. Differences among pod‐color groups in the mean number of chalcid‐damaged seeds were examined using the appropriate LSD with a = 0.05. In each environment, statistically significant differences were found among the four pod‐color groups. Crops harvested from the moist subhumid environment were found to have a severe alfalfa seed chalcid infestation problem throughout the growing season. However, this problem was less severe in the fall. Crops harvested from other environments showed an increasing infestation problem as the cropping season progressed. Harvesting the first, and possibly the second, alfalfa growth of the season for hay and allowing the second or third cut to mature seed (current cropping practice) may present the optimum seed production system for moist subhumid environments. In other environments, using thin stands established in rows and timing the crop to obtain seed in midsummer may reduce the losses currently seen in fall harvests