A dozen agronomic approaches are being thrown at the problem of potato early dying syndrome by a team at a research farm in Carberry, Man.
Led by Mario Tenuta, a soil ecologist from the University of Manitoba, the Canada Manitoba Crop Diversification Centre studies are looking at green manures, soil amendments and fumigation as ways to counter the disease also known as verticillium wilt.
The pathogen, which causes potatoes to wither and die prematurely, has dogged growers for decades, mainly because the spores can remain active in a field for 10 to 15 years even if potatoes are not grown.
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Experiments in other potato producing regions have looked at different green manures, including sorghum and Sudan grass, as possible alternatives.
But one of the most promising solutions may be wafting on the breeze, said Tenuta.
The garlic odour that comes from fields of brassica plants such as canola and mustard is caused by glucosinolates, which are soluble aromatic compounds that have shown promise as pesticides.
“They are the things that have been bred out of canola because they are nasty tasting if you were to eat it. It’s a peppery flavour,” said Tenuta. “As a gas or soluble compound, it can kill pathogens and pests.”
By growing oriental or yellow mustard as green manures, researchers hope to find proof that the number of verticillium spores in the soil can be reduced.
One approach that has consistently shown promise is the application of mustard meal as a soil amendment.
“Within a few hours of applying it to the soil you can really smell garlic,” said Tenuta. “I’m Italian, and it was very difficult for me to leave the field. I really wanted some spaghetti.”
It has the benefit of avoiding the cost of taking a field out of production for a season, but at a cost of $800 per tonne for the food product – and anywhere from five to 10 tonnes per acre is needed for good results – it is unlikely to be used anytime soon, he said.
“I believe that we should first show the utility of these different approaches, then work on getting them to economic and practical levels.”
Lab testing has shown that extracts of Canada milk vetch, a common weed, applied to seed at planting can prevent the development of verticillium wilt throughout the growing season, according to U of M post-doctorate student Abdel El-Hadrami.
Other strategies involve alfalfa green manure rotations with the aim of improving organic matter levels and overall soil health.
Studies in the Pacific Northwest tried growing Sudan grass or sorghum for two to three years continuously to get rid of the pathogen, but so far similar plots at Carberry show inconclusive results.
Vapam, or metam sodium, was also being tested, both for efficacy in controlling early dying and for its long-term effect on the soil.
“One concern with such a really high intensity intervention was the effect on soil ecology. We may one year get rid of the disease, but two or three years later find that we actually have a worse problem than previously,” said Tenuta.
Tracy Shinners-Carnelley, a potato pest specialist with Manitoba Agriculture, said that preventing early dying syndrome begins with a correct understanding of an often complicated issue.
“There are no easy chemical fixes,” she said, adding that it would be difficult to put the range of strategies being studied into use at large-scale operations.
Tenuta said that even correctly identifying the problem is often tough, since salinity and soil fertility problems can mimic the disease, so scouting and correct diagnosis are important.
