Increasing Disease Problems Prompt Crop Rotation Research

Low crop prices and severe disease problems have forced many spring wheat producers to turn to raising alternative broadleaf crops. North Dakota State University researchers are studying new rotations to determine their impact on disease and the need for fungicide applications.

Current recommendations are to plant broadleaf crops, such as canola, no more than once every four years on the same field to avoid severe disease problems.

Researchers at NDSU’s North Central Research Extension Center (NCREC) in Minot have begun a canola rotation study that will continue through 2003. Canola acreage in North Dakota has increased from 18,000 acres in 1991 to more than a million acres this year and is an example of how new crops and rotations are influencing the region’s cropping pattern.

"One of the objectives is to document the influence of crop rotation on the incidence and severity of sclerotinia (white mold), blackleg, and alternaria black spot in canola," according to Brian Jenks, a weed scientist at the NCREC. "Canola growers have designated sclerotinia as one of their top research priorities. Last year was the first year canola growers had any fungicides labeled to control sclerotinia."

Jenks says other goals of the research are to determine the impact of the previous crop on disease levels in canola and determine if fungicide applications can be eliminated or rates reduced by altering the sequence of crops in the rotation. "Canola is fairly new in North Dakota so there hasn’t been a great deal of research up to this point," notes Jenks.

Six crop rotations were established during the 2000 growing season. The rotations consisted of canola, wheat, barley, and flax. A similar study is being conducted in Minnesota where soybean replaced flax. Canola will be sown every year, every other year, every third year, and every fourth year; with broadleaf crops (flax or soybean) sown 1 or 2 years prior to canola.

No differences between crop rotations could be detected yet since this is the first year of the study. However, Jenks says sclerotinia incidence and severity were lower where fungicide was applied compared to no fungicide applied. Canola yield tended to be slightly lower in untreated plots.

Fusarium head blight (scab) levels in wheat and barley were lower where fungicide was applied. Yields for both crops were slightly lower where no fungicide was applied.

According to Jenks, since the study is in its first year, low disease levels were probably a result of crop and cultivation history. The field was in durum the last two years with small grains prior to 1998.

The North Dakota Oilseed Council, Northern Canola Growers Association, and Agricultural Research Institute are providing partial funding for the study.