Potato tubers differ in susceptibility to Phytophthora infestans and several techniques have been used to determine the degree of tuber susceptibility. A comparison of different tuber inoculation techniques based on internal or external placement of inoculum within or on tubers across different cultivars of potato and genotypes of P. infestans was carried out to evaluate the efficiency of inoculation. Internal or external placement of inoculum such as direct injection of sporangial suspension and mycelia colonized agar plug or the soaking method (SM) were the most effective (p ≤ 0.05) in terms of causing tuber late blight. A separate study was conducted to evaluate the interaction between the infection processes of P. infestans and the periderm of tubers of three cultivars of potato differing in skin set development as influenced by harvest date. Mature and immature Russet Norkotah required higher torque to excoriate the periderm indicating improved skin-set compared to the other two (Snowden and Dark Red Norland) cultivars tested. Overall, immature cultivars were more susceptible compared to mature cultivars. Field trials were conducted to evaluate the effects of several different fungicides and biofungicides applied alone or mixed as seed treatments, in-furrow at planting, or in combination (seed + in-furrow treatment) for control of seed-borne P. infestans. The application of fenamidone and fungicides containing mancozeb such as fenamidone + mancozeb, mandipropamid + mancozeb or cymoxanil + mancozeb to potato seed pieces were more effective and improved final plant stand and rate of emergence (p ≤ 0.05) in comparison to othertreatments tested.
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