BEYOND METHYL BROMIDE: NON-CHEMICAL METHODS FOR POSTHARVEST INSECT PESTS OF WALNUTS

Authors: Johnson, Judy; Soderstrom, Edwin; CURTIS, CHARLES - RETIRED ARS; Vail, Patrick

Submitted to: Australian Nutgrower
Publication Type: Trade Journal
Publication Acceptance Date: 4/6/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Current postharvest insect control for dried fruits and nuts depends on the use of methyl bromide and phosphine. Toxicological, environmental, and regulatory concerns, plus possible pest resistance, may limit future use of these fumigants. No single non-chemical method provides an economical alternative to fumigation throughout the postharvest system. Our project integrates short-term disinfestation methods with long-term protective techniques to overcome the limitations of individual alternatives for walnuts. An initial low oxygen treatment (0.4%) for 6 days was followed by one of three long-term treatments: low temperature storage (8-11C), maintenance low oxygen (5%), or a protective Indianmeal moth granulosis treatment. Navel orangeworm and Indianmeal moth were used to evaluate the efficacy of the initial disinfestation treatment and the protective treatments, respectively. No navel orangeworm survived exposure to the initial 0.4% O2 treatment; survival in untreated walnuts was about 80%. No detectable damage due to Indianmeal moth was found in any of the long-term treatments, even after 12 weeks. In contrast, ca. 75% of the untreated nuts showed damage by Indianmeal moth after 12 weeks of storage. High numbers of moths were caught in traps in the untreated room six weeks after the beginning of the long-term test. No Indianmeal moths were caught in either the low temperature or low oxygen treatments. Low numbers of moths (no more than 12/week) were caught in the granulosis treatment. The results of our initial tests are encouraging; the initial low oxygen treatment proved effective in disinfesting walnuts of navel orangeworm, and all three protective treatments kept Indianmeal moth populations at acceptable levels

Technical Abstract: Various environmental and regulatory concerns, plus possible pest resistance, may soon limit use of fumigants for control of postharvest pests of walnuts. Because no single non-chemical method provides an economical alternative to fumigation throughout the postharvest system, our project integrates short-term disinfestation methods with long-term protective techniques to overcome the limitations of individual alternatives. An initial treatment of 0.4% oxygen for 6 days was followed by one of three long-term treatments: low temperature storage (8-11C), maintenance controlled atmosphere (5% oxygen), or a protective Indianmeal moth granulosis treatment. Twenty-five-day old navel orangeworm (fifth instar larvae and young pupae) were used as test insects for the initial disinfestation treatment. Five mated adult Indianmeal moths were added to the long-term treatment rooms each week. No navel orangeworm survived exposure to the initial 0.4% oxygen treatment; survival in untreated walnuts was about 80%. No detectable damage due to Indianmeal moth was found in any of the long-term treatments, even after 12 weeks. In contrast, ca. 75% of the untreated nuts showed damage by Indianmeal moth after 12 weeks of storage. High numbers of moths were caught in pheromone traps in the untreated room six weeks after the beginning of the long-term test. No Indianmeal moths were caught in either the low temperature or the 5% oxygen treatments. Low numbers of moths (less than 12/week) were caught in the granulosis treatment. The results of our initial tests are encouraging; the initial 0.4% oxygen treatment proved effective in disinfesting walnuts of navel orangeworm, and all three protective treatments kept Indianmeal moth populations at acceptable levels.