A practical monitoring program for spider mites, Tetranychus spp., in almond orchards is proposed. It is possible to determine densities of the Tetranychus mites after they disperse through each tree by using the proportion of leaves infested with one or more mites rather than counting the actual number of mites per leaf. This presence-absence (binomial) sampling technique may be used in conjunction with sequential sampling to further reduce sampling time. Provisional control action thresholds developed are 0.436 (mean proportion infested leaves) in the presence of the predatory mite Metaseiulus occidentalis, and 0.220 in its absence. Optimal numbers of trees to be sampled at various confidence levels are determined for a range of mite densities with leaf samples of 5, 15, and 40 per tree.
