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Disease Control and Pest Management

Distribution and Temporal Dynamics of Metalaxyl in Potato Foliage. M. G. Milgroom, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; C. E. McCulloch(2), and W. E. Fry(3). (2)Biometrics Unit, Cornell University, Ithaca, NY 14853; (3)Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 78:555-559. Accepted for publication 20 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-555.

Metalaxyl was sprayed on field plots of potatoes, and leaflets were collected to monitor residues at various times after application. Residues were determined by bioassay separately for each of several thousand leaflets. Residues were highly variable within the canopy at all times. Goodness-of-fit tests showed that metalaxyl residue samples from two-thirds of the plots could have been from censored lognormal distributions. A censored distribution was used because residues determined to be below the detection limit of the bioassay inhibited lesion development in Phytophthora infestans. Median residues decreased exponentially from 100–200 ng/cm² 1 hr after spraying to 5–10 ng/cm² 30 hr later. Subsequent exponential decay rates were much slower. Overhead irrigation 5 or 30 hr after spraying reduced residues in the first day relative to nonirrigated plots. However, 3–5 days later there were no differences in residues in irrigated relative to nonirrigated plots. Time after application was the most important variable for describing the changes in the median residue. Environmental variables such as rainfall, temperature, and humidity were not significant in a regression analysis of metalaxyl residues.