ARS | Publication request: Prevalence and incidence of sunflower downy mildew in North Dakota from 2001 to 2011

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 2013
Publication Date: N/A

Interpretive Summary: Downy mildew is a common disease affecting sunflower grown in North Dakota, the leading sunflower producer in the U.S. Periodic but intermittent surveys were done in the past to enumerate the incidence/prevalence of sunflower diseases, but in the last ten years two organized surveys have collected information annually. The results are compared, and show that downy mildew has been increasing, and that weather alone is not the major factor. In 2011, 70% of ND sunflower fields had some downy mildew, and across the state, it is estimated that 7% of the crop was infected. While sunflower has a unique ability to compensate for plants lost in the seedling stage (due to disease, insect, or other factors), downy mildew was estimated to cause moderate yield losses in 15% of ND fields in 2011. Management options are discussed to minimize the impact of downy mildew.

Technical Abstract: Sunflower downy mildew (Plasmopara halstedii) is an economic problem in sunflowers in North Dakota (ND), which historically produces about half the U.S. sunflower crop. From 2001 to 2011, the prevalence and incidence of downy mildew was monitored in ND as part of two large survey efforts, namely a mid-season survey and a late-season survey. In aggregate, 2,772 fields were evaluated by both surveys. Higher levels of downy mildew were recorded by the mid-season survey, where mean prevalence and incidence were 33.9% and 2.1% respectively, than by the late season survey, where mean prevalence and incidence was 17.3% and 1.15%. Both surveys consistently identified years with high levels of downy mildew but were inconsistent when lower levels of the pathogen were recorded. A clear connection between yearly fluctuations of downy mildew levels to rainfall or to the availability of effective management options could not be made.