Reducing the frequency of seedling malformations in Pinus radiata nurseries by the application of insecticides

The results of three trials undertaken in consecutive years in the Forest Research Institute Nursery, Rotorua, gave strong support to the hypothesis that Thrips tabaci Lindeman is the cause of needle crinkling and multi-leadering in Pinus radiata D. Don seedlings in forest nurseries. Fortnightly applications of an insecticide led to a reduction in the number of thrips present on the seedlings, and a reduction in the number of seedlings becoming multi-leadered. The lowest incidence of malformation occurred in beds of seedlings which had been sprayed at fortnightly intervals with 10 g deltamethrin in water using a spray volume of 100 //ha