Early management of late blight (P infestans) with systemic fungicides

CALDIZ, D.; ADRIANA BALBINA ANDREU

Lethbridge, Canadá

Conferencia; AgCON 2006. 6th McCain World Class Agriculture Conference.; 2006

McCain Food

Currently, all potato-producing areas are at risk of infection from late blight with consequences on tuber yield and quality. A significant source of inoculum are the seed pieces with non-detectable infection levels. Seed transport has contributed in spreading aggressive metalaxyl-insensitive isolates to all potato-producing areas both in Argentina and in the rest of the world. In Argentina the mating type A2 is the most frequent and aggressive. Fungicides containing Mancozeb are known to be effective in protecting seed tubers from contamination by Phytophthora infestans. However, treatment of seed potatoes with contact fungicides, such as Mancozeb, only can protect healthy seed tubers from infections caused during handling but can not protect the young plant after emergence when it is more susceptible to late blight This research work was carried out in order to assess the effect systemic fungicides applied to seed tubers before planting upon foliage protection early in the season in different cultivars under different environmental conditions and soil types.Acrobat applied to seed tubers, immediately after cutting, protected the foliage against artificial inoculation of Phytophtora infestans. In all cultivars average disease severity index (DSI) was higher for the control than for the treated seed tubers. Average DSI for cvs. Shepody, Kennebec, Russet Burbank and Ranger Russet were 2, 2, 4 and 4 respectively, by 30 days after crop emergence, at the 4 kg.ha-1 dose. The 2 kg.ha-1 dose was only effective for 10-15 days after crop emergence. Melody Duo applied immediately after cutting of the seed tubers protect the foliage against artificial inoculation of P. infestans. For all cultivars the average disease severity index was higher for the control treatment than for those treated tubers. Average DSI for cvs. Shepody, Kennebec, Russet Burbank and Ranger Russet were 2.0, 2.0, 3.5 and 3.8 for the period emergence up to 30 days of crop growth. The same was true for the foliage protection percentage which was higher in those crops from treated tubers. For cvs. Shepody, Kennebec, Russet Burbank and Ranger Russet the average values were 78, 75, 60 and 50% for Iprovalicarb + propineb (dose 1.5 kg.ton-1 of seed) for the same period.It is concluded that Acrobat and Melody Duo applied immediately after tuber cutting protect tubers and early foliage against Late blight infections up to 40 days after crop emergence. These treatments should be part of an integrated Late Bligth management program in order to reduce agri-chemical use and improve control efficiency.