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

The economic threshold of burrowing (Radopholus similis) and lesion nematod e (Pratylenchus goodeyi) on banana may be used to determine whether it is e conomic to apply nematicide. However, to use such a threshold, a sampling s trategy is essential to determine the severity of root damage caused by the nematode. Ten banana crops in south-eastern Queensland and northern New So uth Wales and 10 in northern Queensland were sampled several times over sev eral 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 t o determine the relationship between the mean and variance of the disease i ndex and nematode populations. Taylor's power law gave the better fit, and was therefore used to determine fixed-precision stop lines for sequential s ampling for precision at 20-30% for disease index and 20-40% for nematode p opulations. Twenty samples per crop were sufficient to achieve 25% precisio n when assessing nematode infestations using disease index but only 40% pre cision when using nematode populations.