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Field experiments with chlorophacinone (CPN) ground sprays seem to be more effective in control of pine voles in North Carolina orchards when the percentage grass cover under tree drip lines is high. Preliminary laboratory results seem to confirm this observation.
Our group has carried out a number of field trials of the efficacy of ground sprays for controlling pine voles in orchards. In reviewing these tests with special reference to inconsistency of results with chlorophacinone (Hayne 1977) an apparent relationship to the amount of grass cover was noted, and laboratory trials were started to test this question.