Soil fumigation is a good option for potato acres inflicted by yield-limiting pests, says Andy Robinson, a North Dakota State University extension potato specialist.
Fumigation is used south of the border to control buildup of soil-borne pests causing verticillium wilt, potato early dying and other diseases.
But fumigation hasn’t been widely adopted in Canada, unlike the U.S., where producers are used to treating soil with metam sodium (trade name Vapam or Busan) and other fumigants post-harvest in preparation for spring planting.
Robinson was at Manitoba Potato Production Days in January to discuss preliminary findings from the first year of a study that asks whether reduction in disease pressure will allow potato plants to use nitrogen more efficiently.
The study is part of a larger project with University of Minnesota soil ecologists and NDSU pathologists that will look at nutritional requirements of crops following fumigation (with metam sodium or chloropicrin) as well as the impact of fumigants on microbial communities.
In his presentation, Robinson pointed to a Wisconsin study showing a 20 per cent yield increase following fumigation and a continual response with nitrogen. In that study, nitrogen tended to peak in untreated soils.
So far, one year of data from Robinson’s study shows similar results, with improved yields overall and continual N response in the fumigated plots.
Robinson says fumigation is a major investment in the U.S., where application can cost between US$200 and US$300 per acre. In Canada, costs can run up to $500 per acre.
But the benefits can be worth it in soils with significant problems, he says, bumping yields and potentially reducing N requirements.
Mario Tenuta, a professor of applied soil ecology at the University of Manitoba, has conducted about 10 trials since 2007 with metam sodium in Manitoba’s main potato-growing regions.
“We’ve been looking at verticillium levels in the soil as a result of the fumigation, as well as yield,” he said.
“In those soils that do have potato early dying, with high associated population counts of verticillium, the Vapam can reduce disease quite significantly, and that results in the potato crop living longer and putting on more tuber mass in late summer, so we come out with greater yields. But only a few fields have been responsive to the fumigation. The majority is not responsive. For those fields, it represents a heavy cost and not much payoff.”
Producers and processors are “super interested” in fumigation to improve efficiency and increase yields, Tenuta says. But it’s not a one-size-fits-all solution.
He recommends producers fumigate if marketable yields are much lower than what they’ve seen in the past, and if they obtain a verticillium soil analysis that shows verticillium counts in the hundreds.
Tenuta’s estimation is that roughly a quarter to a third of potato fields in Manitoba might benefit from fumigation — particularly those where producers have stopped growing potatoes because the land is considered “old” or “tired” potato land and yields are poor.
He’s hoping to work with colleagues in Atlantic Canada on a joint fumigation project with new potato cluster funding. “We want to tackle this ‘tired potato land’ question or low-yielding spots in the field to see if we can boost yields,” he says. “One approach could be fumigation, but it’s not the only approach we’ll look at.”
In New Brunswick, McCain has conducted trials with the broad-spectrum fumigant chloropicrin since 2014.