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Dispersion Statistics and Sequential Sampling Plan for Leaf Blight Caused by Botrytis squamosa in Onions. Guy Boivin, Research Station, Research Branch, Agriculture Canada, Saint-Jean-sur-Richelieu, Québec, Canada, J3B 6Z8; Pierre Sauriol, Ministère de l' Agriculture, des Pêcheries et de l' Alimentation, 118 rue Lemieux, Saint-Rémi, Québec, Canada, J0L 2L0. Phytopathology 74:1385-1387. Accepted for publication 14 June 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1385.

The spatial distribution of Botrytis 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 one-half lesion per leaf as the economic threshold. At least ten one-leaf samples were needed to detect significant differences from the critical threshold of one-half lesion per leaf and up to 54 leaves were needed when the disease level was at or near the half-lesion-per-leaf threshold.

Additional keywords: economic threshold, mean crowding.