VIEW ARTICLE

Disease Control and Pest Management

Evaluation of Clear Polyethylene Mulch for Controlling Verticillium Wilt in Established Pistachio Nut Groves. L. J. Ashworth, Jr., Plant pathologist, Plant Pathology Department, University of California, Berkeley 94720; S. A. Gaona, superintendent, Pistachio Department, Blackwell Land Management Company, P. O. Box 2446, Bakersfield, CA 93303. Phytopathology 72:243-246. Accepted for publication 12 June 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-243.

Complete mulching of the soil surface of a 6-yr-old, drip-irrigated planting of pistachio nut trees with clear polyethylene sheeting for 2 mo resulted in elimination of Verticillium dahliae (undetectable amounts to 0.07 microsclerotia [MS] per gram in air-dry soil) to a depth of 120 cm. Initial inoculum densities at 30, 60, 90, and 120 cm were, respectively, 4.6, 0.9, 0.6, and 0.4 MS/g soil. Mulching was effective whether or not the soil was preirrigated with sprinklers before mulches were applied early in July. Complete mulching was much more effective than treatments in which polyethylene sheets were separated by 0.5 or 1.2 m at tree rows. One year following mulching in 1979, average infection percentages were 6.3, 1.6, 3.4, and 3.4, respectively, for the unmulched, completely mulched, and mulch treatments in which the polyethylene sheets were separated by 0.5 and 1.2 m in the tree rows. Thus, disease control was, at best, about 75%. Soil temperature at the 0–30 cm depth under mulches accounted for the demise of V. dahliae. Temperature did not, however, account for loss of MS at 60, 90 and 120 cm.