Designing Orchard Experiments for European Red Mite Control1

Abstract

Experiments based on preventive programs have created a need for satisfactory designs to evaluate acaricides under orchard conditions and to permit statistical summarization and interpretation of the results. The literature regarding mite sampling is briefly reviewed and two examples of preventive experiments and one eradicant type experiment are presented with statistical treatment and interpretation of results. Data from orchard mite control experiments, in which counts were taken periodically during the season, were analyzed statistically as split-block designs. Before analysis of variance could be conducted, a logarithmic transformation was necessary to remove the proportional relationship between the means and the standard deviations to meet the requirements of an F test. By increasing the number of trees a greater gain in detecting treatment differences was produced than by increasing the number of leaves sampled or the number of sampling dates. In an example using mild acaricides in a preventive schedule, it was found that the addition of 1 ounce of ovex in each spray to a DDT-parathion formulation gave superior control of the European red mite, Panonychus ulmi (Koch). Glyodin used in place of captan also significantly improved control. A DDT Diazinon (O,O-diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate) tank mix was as effective as most DDT-parathion formulations. Differences in the other experiments represented were large in one and small in the other, but were not significant in either.