Graduation date: 2007Field trials were conducted during 2001 to 2003 to investigate soil population dynamics of Meloidogyne chitwoodi, tuber symptom suppression using oxamyl, and post-harvest tuber symptom development on short-season potato varieties Russet Norkotah and Russet Nugget (San Luis Valley only). The experiments were located in the San Luis Valley in Colorado, Klamath Basin in Oregon, and southern Columbia Basin in Oregon to represent, cool, warm, and hot growing regions, respectively. M. chitwoodi soil population dynamics were multi-modal in all three regions representing distinct periods of egg hatch and root and tuber infection. M. chitwoodi completed two generations in the cooler production areas of the Klamath Basin and San Luis Valley, and three generations in the hot region of the Columbia Basin. When left uncontrolled, M. chitwoodi infected and caused tuber symptoms in all three regions, but tuber symptoms were significantly reduced with the use of a bi-weekly oxamyl program that began at the hatch of the second generation. Furthermore, augmenting with in-furrow at-planting and crop emergence applications provided better protection. The level of reduction in symptoms using the application schedules outlined in this research was substantially better than that previously observed with this nematicide. Oxamyl did not control M. chitwoodi densities in the soil. For that reason, internal and external symptoms increased when harvest was delayed by three weeks in the Columbia Basin regardless of whether or not oxamyl had been applied. Following harvest in the Columbia Basin and Klamath Basin there is potential for internal symptom development if tubers are stored warm. The percentage of tubers with internal symptoms increased when stored at 21-24°C and more than 740 post-harvest DD5C were accumulated, regardless of whether or not oxamyl was used. However internal symptoms did not increase during long-term cold storage (3-5°C) when no more than 480 – 610 post-harvest DD5C were accumulated. Unlike internal symptoms, there was no increase in external symptoms following harvest even when as many as 1,000 post-harvest DD5C were accumulated. Oxamyl is currently the only chemical that growers can apply during the growing season to suppress tuber damage from M. chitwoodi and reduces symptoms on short-season potato cultivars in both cool and hot growing regions in the western United States.