Abstract
AbstractA 5-year survey of Saskatchewan alfalfa (Medicago sativa L. sensu lato) seed fields was undertaken to determine the level of infestation by the alfalfa seed chalcid, Bruchophagus roddi (Gussakovsky). Seed samples were taken from commercial seed fields, hay fields, and roadsides just before pod maturity. From sample lots of 250 pods, the numbers of healthy, chalcid-damaged, and frozen or immature seed were determined. Later, producers were questioned about the attributes of and management practices employed in their fields. Seed yields and infestation levels were correlated with temperature, precipitation, and degree-day data from the year of and the year preceding seed collection. Alfalfa seed chalcid infestation level was correlated most closely with the temperature and rainfall in July and August of both years. The proportion of damaged seed was highest the year following warm, dry summers. Alfalfa cultivar also influenced infestation levels; winter-hardy cultivars that became dormant early in the autumn had lower levels of chalcid-damaged seeds than less hardy cultivars which maintained growth later in the season. Management practices such as the use of insecticides (for plant bug and aphid control), fertilizers, and herbicides, size or age of field, soil type, and application of irrigation water did not affect the proportion of seeds injured by chalcids.
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