Two concentrations of dimethoate were applied with a hydraulic ground sprayer to cone-bearing Douglas-fir and grand fir trees. Single application (mid-June) and a double application (mid-June and mid-July) were compared. Three of the four treatments applied to Douglas-fir resulted in a significantly higher number of sound seeds produced per cone compared to untreated cones. No seed protection was exhibited in the grand fir treatments.
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