Abstract
An experiment was undertaken to determine the value of dormant oil and dormant oil-insecticide mixtures for control of the pear psylla, Psylla pyricola Forster. Delayed dormant application of dormant oil-lime sulfur mixture was as effective as a dormant application made 9 days earlier. The dormant oil-lime sulfur mixture was less effective than dormant oil alone. A dormant oil of 405 seconds Saybolt viscosity at 100° F was more persistent and more effective than an oil of 205 seconds viscosity. Polybutene (Indopol H-100) provided initial control equal to the more viscous dormant oil, but reinfestation occurred within 3 weeks. Analysis showed the polybutene to be an extremely persistent compound. Dormant oil-dinitrocresol provided the best control. The mixture reduced the adult population to low numbers and prevented egg deposition on the twigs for 30 days. None of the spray mixtures were phytotoxic. The plots treated with dormant oil (205 vis.), experimental dormant oil (405 vis.), and dormant oil-dinitrocresol did not show psyllid numbers at treatment level until late July.
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