PORTAGE LA PRAIRIE, Man. – A plant pathologist with the United States Department of Agriculture suggests reduced tillage can lead to an increase in crop diseases.
During the annual meeting of the National Sunflower Association of Canada, Thomas Gulya said reduced tillage has its merits, especially for conserving soil and moisture, but a consequence is that the pathogens that infect crops can accumulate on the soil surface, where they face a less hostile environment than if tilled into the soil.
Crop residue often serves as a host for disease-causing pathogens. Gulya said by turning the residue into the soil through tillage, the pathogens are exposed to bacteria and other pathogens that can break them down.
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Gulya is based in Fargo, North Dakota, where he specializes in research on sunflower diseases. He shared his thoughts on reduced tillage while talking about diseases common to sunflowers and the various methods for combatting them.
He emphasized a multi-faceted approach to managing diseases in sunflowers. Fungicides and varieties with improved resistance can be useful, he said, but producers should not ignore the basics of tillage and crop rotations.
David Kaminski, Manitoba Agriculture plant pathologist, said pathogens on the soil surface are exposed to things such as freezing and thawing, wet and dry conditions and the sun’s ultraviolet rays.
He said tillage may not be the answer for dealing with pathogens because there tends to be little biological activity at a depth of 15 centimetres to break them down. While conditions within the top 2.5 cm of soil can prove hostile for pathogens, there are fewer microorganisms at a depth of 15 cm and the soil is cooler and potentially drier.
In the case of sclerotinia, the pathogens can survive for years if plowed into the soil, Kaminski said. Those pathogens could be returned to the surface if the field were to be plowed again within three years, he said.
“The sclerotinia is kind of in suspended animation down there.”
Gulya said including crops such as wheat and barley in the rotation can help break the disease cycle in sunflowers. Research at North Dakota State University shows that crambe and canola should be avoided in the rotation before planting sunflowers.
“Crop rotation can have a very big impact,” Gulya said. “It should not be dismissed lightly.”
Rust, sclerotinia, downy mildew and verticillium were among the most prevalent diseases in Manitoba this past year. In North Dakota, sclerotinia wilt and verticillium were the most common diseases.
Some sunflower diseases can persist while others fluctuate, meaning that each year can bring different challenges.
“The growing conditions change year to year and the problems change year to year,” Gulya said.
