A sampling strategy to assess banana crops for damage by Radopholus similis and Pratylenchus goodeyi

Abstract

The economic threshold of burrowing (Radopholus similis) and lesion nematode (Pratylenchus goodeyi) on banana may be used to determine whether it is economic to apply nematicide. However, to use such a threshold, a sampling strategy is essential to determine the severity of root damage caused by the nematode. Ten banana crops in south-eastern Queensland and northern New South Wales and 10 in northern Queensland were sampled several times over several years to determine the disease index (percentage cortical root damage caused by R. similis and P. goodeyi) and nematode populations in roots. The negative binomial distribution and Taylor’s power law analysis were used to determine the relationship between the mean and variance of the disease index and nematode populations. Taylor’s power law gave the better fit, and was therefore used to determine fixed-precision stop lines for sequential sampling for precision at 20–30% for disease index and 20–40% for nematode populations. Twenty samples per crop were sufficient to achieve 25% precision when assessing nematode infestations using disease index but only 40% precision when using nematode populations.