Dispersion Statistics and Sequential Sampling Plan for Leaf Blight Caused byBotrytis squamosain Onions

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Abstract
The spatial distribution of B. squamosa on onions was studied by using Iwao''s patchiness regression technique. The basic components of the Botrytis leaf blight lesion population were aggregates that were distributed contagiously in onion fields. Fungicide treatment did not alter this spatial distribution. This information was used to prepare a sequential sampling plan with 1/2 lesion per leaf as the economic threshold. At least 10 one-leaf samples were needed to detect significant differences from the critical threshold of 1/2 lesion per leaf and up to 54 leaves were needed when the disease level was at or near the half-lesion-per-leaf threshold.