Spatial distribution pattern and sequential sampling plan for Paratylenchus dianthus

Abstract

The analysis of spatial distribution pattern and a sequential sampling plan for Paratylenchus dianthus (Jenkins et Taylor) are reported. The study was carried out from April 1982 to 1984 in a commercial crop of carnations grown in a greenhouse in the province of Naples. The analysis of spatial distribution was made by taking 100 soil samples, within a stratifie'd-random design, every two weeks and using Iwao's regression of mean crowding (m) on the mean (m). Changes in spatial distribution were determined with Lloyd's index (patchiness index). It emerged that the basic components of population were gruups uf individuals with an aggregated distribution. The level of aggregation decreased as the mean density of population increased. Subsequently m~' on m regression was used, according to Iwao's method, to carry out a sequential sampling plan. In the conditions of this study, the highest number of samples to be taken to reach a decision with a 95% confidence level is 79 when the mean density of population present in the field (m) is close to the economic threshold of 250 nematodes/l0 ml of soil. When the mean density is much greater or much lower than the economic threshold (treatment necessary or unnecessary) the decision is reached after a few samples.