Sequential sampling plans for nematodes affecting sugarcane in Queensland

Abstract

The dispersion characteristics of root-lesion, root-knot, spiral, stubby-root, stunt and ring nematodes in soil, and root-lesion, root-knot and spiral nematodes in roots in sugarcane fields, were determined in studies in southern Queensland. The Poisson distribution, negative binomial distribution, Iwao's regression model and Taylor's power law analysis were used to determine the relationship between mean and variance of nematode counts. All methods showed that nematodes were aggregated (Iwao's G 1.12-1.65, Taylor's b 1.10-1.76). In general, Taylor's power law gave better fit compared with the other models (R2>0.61). Relationships to determine sample sizes for fixed levels of precision and fixed-precision-level stop lines for sequential sampling were developed for all species. There were functional relationships between variance and mean of untransformed population counts for all species, but suitable transformations eliminated significant correlations in most cases.