Pink rot (Phytophthora erythroseptica) in potatoes is ubiquitous in Canada. When 500 potato growers attended Manitoba Potato Production Days earlier this winter, they were all ears for the latest results on suppressing this disease.
“It’s largely a tuber issue,” says Rick Peters, Agriculture and Agri-Food Canada’s potato researcher in Charlottetown, Prince Edward Island, although all underground tissues can be infected. “You see it especially in wetter falls when resting spores germinate and you get a ‘swimming spore’ that enters through the eyes of the tubers – stolons can be infected earlier in the season after which the pathogen moves down the stolon into the tuber.”
For the last decade, in-furrow treatment or foliar sprays of Ridomil (metalaxyl-m), applied at tuber initiation and two weeks later, have suppressed this disease. However, resistance is building to this chemistry, first noticed in New Brunswick in 2005 and also in Maine and North Dakota. Not until 2012, did this phenomenon reach Prince Edward Island.
Industry rallied including Syngenta, Ridomil’s manufacturer and grower groups from PEI, Manitoba and Alberta to fund broader research. Samples were taken across Canada in 2013 and 2014, confirming levels of 50 per cent resistance in Ontario and provinces east. Only a few isolated cases of resistance were identified in Manitoba and Alberta.
Peters recommends that a national survey on the incidence of Ridomil resistance in pathogen populations be continued. Data for individual farms can provide the basis for pink rot management decisions. More research into alternative disease control strategies is required. Phospites may play a more important role in the management of pink rot if Ridomil resistance becomes more widespread. Other in-furrow treatments to manage pink rot in daughter tubers appear promising.
To date, products such as Confine Extra, Rampart and Phostrol have been applied to foliage with good results for disease suppression. Their positive environmental profile is also good news in this story, says Peters.
It’s largely a tuber issue. You see it especially in wetter falls when resting spores germinate and you get a ‘swimming spore’ that enters through the eyes of the tubers.
~ DR. RICK PETERS