Oklahoma State University Stillwater, OK
Oklahoma Alfalfa Oklahoma Cooperative Extension Service Oklahoma Agricultural Experiment Station

PROPER PLANNING FOR SEED PRODUCTION AND THE CONTROL OF ALFALFA SEED CHALCID
If seed production is planned, it is important that a control program for the seed chalcid be started during May, as this species cannot be controlled by insecticide applications during production of the seed crop. This is because adult wasps insert eggs inside of seeds within the pods, and larval and pupal stages develop inside the alfalfa seeds. The chalcids overwinter as pupae in seed that was spilled in the previous season or in seed that was produced by alfalfa growing in field border areas and roadsides.    Adults emerging in May and June lay eggs in seed being set on alfalfa wherever it is available, with the most common seed source being plants growing outside of fields. Several generations of the chalcid are completed each year, with the levels of infestation in seed becoming progressively higher as chalcid populations increase in mid- and late summer. Research has shown that up to 80% of seed harvested in September may be infested. There are two management approaches that should begin in May to help in reducing levels of infestation in the seed crop.    The first of these is to keep volunteer alfalfa outside of field areas clipped as much as possible to prevent seed set and remove potential habitats for population increases of the chalcid. Secondly, it is important to begin growth for the seed crop after the first forage harvest in May, so that seed can mature and be harvested in late July or early August. This harvest timing will be early enough to avoid the highest levels of infestation by the chalcid during late August and September.
Richard Berberet, Alfalfa Entomologist  Department of Entomology and Plant Pathology  Oklahoma State University

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