VIEW ARTICLE

Disease Detection and Losses

Spatial Pattern and Sequential Sampling Plan for Meloidogyne hapla in Muck-Grown Carrots. Guy Bélair, Nematologist, Research Station, Research Branch, Agriculture Canada, Saint-Jean-sur-Richelieu, Québec, Canada J3B 6Z8; Guy Boivin, entomologist, Research Station, Research Branch, Agriculture Canada, Saint-Jean-sur-Richelieu, Québec, Canada J3B 6Z8. Phytopathology 78:604-607. Accepted for publication 2 December 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-604.

Iwao’s patchiness regression technique was used to study the spatial dispersion of Meloidogyne hapla in muck-grown carrots. A gall index ranging from 0 to 5 was used to estimate the population densities of the northern root-knot nematode in the fields. This gall index was positively correlated with carrot yield losses in microplots and commercial fields. With current control strategies and production return, a 40% yield loss was established to be the economic threshold for M. hapla. This yield loss corresponds to a gall index of 1.6 for the current season and 0.65 for the preceding season. The basic components of the population were aggregates randomly distributed in carrot fields. This information was used to calculate a sequential sampling plan that requires a minimum of 10 samples and a maximum of 72 samples to determine if the mean gall index of a field is significantly different from 0.65 and if control measures are necessary for that field the following year.