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Relationship between Population Densities of Heterodera schachtii and Losses in Vegetable Crops in Ontario. T. H. A. Olthof, Nematologist, Research Station, Research Branch, Agriculture Canada, Vineland Station, Ontario, L0R 2E0; J. W. Potter(2), and E. A. Peterson(3). (2)Nematologist, Research Station, Research Branch, Agriculture Canada, Vineland Station, Ontario, L0R 2E0; (3)Microbiologist, Chemistry and Biology Research Institute, Research Branch, Agriculture Canada, Ottawa, K1A 0C6. Phytopathology 64:549-554. Accepted for publication 2 November 1973. DOI: 10.1094/Phyto-64-549.

Five vegetable crops were grown in microplots infested with 0, 666, 2,000, 6,000, or 18,000 sugarbeet nematode larvae (Heterodera schachtii) per kg of soil. In general, marketable yields were inversely correlated with preplant nematode population densities, except for cauliflower which was not affected at any preplant density used. Losses in marketable yields of rutabagas were 15%, 22%, and 35%, respectively, at the three highest preplant densities; those of spinach were 29% and 49%, respectively, at the 6,000 and 18,000 densities. At the 18,000 density, losses in marketable weight of cabbage and table beets were, respectively, 24% and 30%. Larval populations in the soil were higher at harvest than at planting under all crops except spinach. At the 18,000 density, there were 210,000 nematodes per kg of soil under cabbage, 98,000 under beets, 90,000 under rutabagas, 46,000 under cauliflower, and 2,900 under spinach. The number of H. schachtii cysts in the soil at harvest increased with increasing larval population densities per kg of soil and amounted to 720 under cabbage, 530 under rutabagas, 470 under beets, 400 under cauliflower, and 240 under spinach, for the 18,000 density. The number of H. schachtii cysts per root system, and the number of cysts per gram of fresh root, were also positively correlated with preplant densities in all crops.

Additional keywords: population dynamics, economic loss threshold.