Geographic incidence and damage levels of alfalfa seed chalcid, Bruchophagus roddi (Hymenoptera: Eurytomidae), in Saskatchewan, and its relationship to weather and agronomic variables and production practices

摘要

A 5-year survey of Saskatchewan alfalfa [lucerne] seed fields was undertaken to determine the level of infestation by the lucerne seed chalcid (Bruchophagus roddi). Seed samples were taken from commercial seed fields, hay fields, and roadsides justbefore 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, rain, and degree-day data from the year of and the year preceding seed collection. The infestation level of B. roddi 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. Lucerne cultivar also influenced infestation levels; winter-hardy cultivars that became dormant early in the autumn had lower levels of chalcid-damagedseeds than less hardy cultivars which maintained growth later in the season. Management practices, such as the use of insecticides, fertilizers, and herbicides, size or age of field, soil type, and application of irrigation water, did not affect the proportion of seeds injured by B. roddi.