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Pig manure, fish emulsion kills powdery scab in spuds

A scientist studying potato scab has found soil treatment can alter disease impact.

A scientist studying potato scab has found soil treatment can alter disease impact.

Dr. George Lazarovits of the Agriculture and Agri-Food Canada office in London, Ontario, said he’s found liquid swine manure and fish emulsion are tremendously successful at killing powdery scab in potatoes.

The fatty acids of swine manure are the “number one means of killing scab,” Lazarovits said, citing research that found a 75 per cent reduction of scab at one site.

He explained that the swine manure is anaerobic fermented material, which turns into vinegar or fatty acids. “It’s the fatty acids that are acting as the number one means of killing scab,” he said.

“The problem is, some of the swine manure doesn’t have enough active ingredients because it’s too diluted … and vinegar only acts as an antibiotic under acid conditions, so if you have an alkaline soil, that material is useless.”

Results for the fish emulsion, or “fish soup,” are still in the preliminary stages, he said.

“We still don’t know how to use it. We know it works, but we don’t know why and we don’t know how to put this fish emulsion in the right way to make it economically feasible.” He added there were “phenomenal” yield increases, in some cases triple yield, when fish emulsion was added to soil. However, he noted research plots were conducted in micro-plots.

Research found there was “significant reduction” in potato scab nematodes with acidified liquid swine manure. He noted the pathogens are killed yet the beneficial agents are not, calling it “selected disinfestations.” Lazarovits said he suspects the acidified liquid swine manure is toxic only to dormant pathogens and not to metabolically active pathogens. Still, research continues, he noted.

Several studies are underway looking at detection of potato scab in seed potatoes, including gene study. Lazarovits said one of the challenges facing researches is that many pathogens are similar looking, making it difficult to identify the potato scab pathogens. Tests on disinfesting seeds were also conducted, Lazarovits explained. In 2004, 41 lots were tested, 11 of which had potato scab and 19 with no scabby tubers. Lazarovits said that, despite rinsing, scab bacteria were still present. Only when disinfested with a bleach wash and alcohol dip did daughter tubers have 100 per cent marketability, he said.

Lazarovits made the presentation recently in Moncton recently as part of A&L Canada Laboratories Potato School.