Effect of the plant growth regulators paclobutrazol and chlormequat chloride on pear psyllid (Cacopsylla pyricola (Foerster)) and pear rust mite (Epitrimerus piri (Nal.))

Summary

Following programmes of four to six sprays of paclobutrazol and chlormequat chloride on pear cv. Conference, population densities of pear rust mite (Epitrimerus piri) were reduced by ca. 60% compared with unsprayed trees. Population densities of pear psylla (Cacopsylla pyricola) on paclobutrazol-treated trees were about half those on untreated ones, but were not affected by chlormequat chloride. In laboratory bioassays, chlormequat chloride was toxic to pear rust mite at concentrations well below field rates. Chlormequat chloride was not toxic to pear psylla larvae, and adults were affected only at rates well above those used in the field. Paclobutrazol showed no acute toxicity to either pest species.