Impact of Crop Rotation and Sequence on Disease Incidence and Severity in Canola.
Denise M. Markle, Brian Jenks, Gary Willoughby, and Carl A. Bradley. North Dakota State Univ, 5400 Highway 83 South, Minot, ND 58701
Recent announcements for canola biodiesel production in North Dakota have increased interest in growing canola in ND. Biodiesel plants may require increased canola production in the state. In addition, scab, and low market prices have forced many small grain producers in the northern plains to turn to alternative broadleaf crops. Current recommendations are to plant a broadleaf crop like canola or sunflower no more than once every four years to avoid buildup of disease inoculum. Additional information on the impact of crop rotation on disease would help producers optimize their limited resources. A four-year rotation study was initiated in 2000 to determine the impact of preceding crops on disease incidence and severity in canola. Six rotations were evaluated and every phase of the rotation is present every year in a randomized complete block design replicated four times. The rotations consist of canola every one, two, three, or four years preceded by canola, flax, or wheat. Half of each canola plot was treated with fungicide to prevent Sclerotinia stem rot (SSR). Plots were evaluated for SSR risk; SSR and blackleg incidence and severity; and yield and test weight. The objectives of this research were to: document the influence of crop rotation on the incidence and severity of sclerotinia, and blackleg in canola; determine the impact of the previous crop on disease levels in canola; and determine if fungicide applications can be avoided by altering the sequence of crops in the rotation. To date, general observations on disease risk and incidence indicate it is more dependent on environment than rotation. In general, blackleg incidence has increased from 2000 to 2006 across all rotations in the study. However, blackleg severity has remained low. This may be because only canola varieties rated moderately resistant or resistant have been used in the study.