SOIL SOLARIZATION TO CONTROL VERTICILLIUM-DAHLIAE AND PRATYLENCHUS-PENETRANS ON POTATOES IN CENTRAL ONTARIO

Effects of soil solarization were studied in two potato fields near Alliston, Ontario. Plots were covered with transparent plastic or left uncovered for 8 weeks from mid June to mid August. The average daily temperatures of the soil were 7-10-degrees-C higher at all measured depths in solarized plots than in uncovered plots. Solarization increased three-fold the concentrations of nitrogen within the top 10 cm of soil but not at lower depths. Populations of free-living nematodes and of the root-lesion nematode Pratylenchus penetrans were significantly reduced (by about 50%) in the surface layer of solarized soil. Natural populations of Verticillium dahliae, and of microsclerotia of the fungus buried at the onset of solarization, were significantly reduced or eliminated from the upper 5 cm of soil in solarized plots. At depths of 15 cm and 30 cm, mortality of microsclerotia was 73% and 54%, respectively. Viability of microsclerotia was not reduced in uncovered soils at any depth. Growth of soybean, corn, and eggplant in solarized soil was increased significantly under controlled conditions only in soil from the top 10 cm. Potato cultivars Norchip, Kennebec, and A66107-51 planted the following year had a lower incidence of verticillium wilt in solarized soil. Yield increases ranged from 10% to 43% in solarized plots but were not statistically significant. Under the climatic conditions of central Ontario, solarization is an effective soil disinfestation procedure for the top 10 cm of soil.