Early management of late blight (Phytophthora infestans) by using systemic fungicides applied to seed-potato tubers

Planting of seed tubers infected with late blight has been reported as a major cause in initiating the disease at field level. Seed treatments with contact fungicides can protect healthy tubers from infection during handling, grading and cutting before planting, but are not effective in protecting the young plant after emergence, when is more susceptible to the disease. Foliar fungicide applications are still required so crop protection early in the season, as a consequence of seed treatments could be an advantage especially in environments conducive to late blight epidemics. The systemic fungicides iprovalicarb+propineb (Melody Duo) and propyl carbamate (Previcur N), from Bayer CropScience, were applied to seed potato tubers (40–50 g) immediately after cutting or at planting to the bottom of the furrow and seed piece in cultivars Kennebec, Shepody, Ranger Russet, Russet Burbank and Spunta, at doses of 0.8 and 1.6 kg ton−1 and 0.4 and 0.8 l ton−1 of seed, respectively. Treated and control seed tubers were planted in pots in a greenhouse. From the time plants had one fully expanded leaf up to 40 days after emergence each treatment was evaluated by the detached-leaf method to assess foliage protection by means of artificial late blight inoculation. For all cultivars a higher level of foliage protection was found in those plants from seed tubers treated with iprovalicarb+propineb, while no effects were observed when the chemical was applied at planting to the bottom of the furrow. Used as described, this fungicide provided a higher protection against late blight than propyl carbamate. Further pre-commercial field trials, carried out during two growing seasons, with iprovalicarb+propineb was effective in protecting the foliage of cultivars Spunta, Kennebec and Shepody up to 4–6 weeks after crop emergence. For the first 4 weeks protection was high and the following two weeks it was satisfactory. This innovative application of iprovalicarb+propineb was only effective when the chemical was applied to cut seed tubers immediately after cutting and before suberization. Due to its effectiveness in controlling late blight this type of treatment should be part of a strategy for integrated late blight management, particularly where late blight epidemics occur early in the season.