by Dr. Charla Hollingsworth, U of MN Extension Plant Pathologist
Early lifecycle stage structures (pycnia) of sunflower rust were detected on volunteer sunflowers during early-June in Minnesota and North Dakota (Figure 1). These detections created concern because that meant:
the fungus was only two spore stages away from producing the spores responsible for epidemics (pycnia → aeciospores → urediospores);
it was much too early in the growing season to see rust developing; and
the fungus had overwintered in our agroecosystem in its sexual stage. A possible outcome of winter survival is the potential for genetic recombination by the pathogen where more virulence might occur on sunflower varieties grown here.
Where is it?
Last week, Craig Hanson (BASF) detected a cropped sunflower field in NW Minnesota with pycnia on approximately 25% of plants. Since then, Minnesota Dept. of Ag (MDA) Plant Pest surveyors have been targeting sunflower fields to determine the risk of a sunflower rust outbreak. Ardell Knudsvig, MDA surveyor in NW Minnesota has found pycnia to be widespread on cropped sunflowers in fields he surveyed in Red Lake (18% incidence), Polk (13% incidence), and Pennington Counties (14% incidence) within the last week. On Tuesday, July 7 he surveyed four fields in Roseau and one of them had pycnia (13% incidence), and two fields in Marshall didn't have symptoms.
The good news is that uredial pustules have not yet been detected, so the pathogen's lifecycle stages are progressing more slowly than first expected. Since average crop growth is behind for this time of year, this is encouraging. Unfortunately, pycnia are widespread in fields which increases the likelihood that when uredial pustules are produced, they will also be widespread. This could increase the likelihood of crop loss from rust.
Scout, scout, scout.
Producers need to scout sunflower fields regularly to determine if rust is becoming established in fields. During 2008, North Dakota had localized rust epidemics with observed crop losses from fields that were not protected with fungicide. Once urediospores are produced (Figure 2), rust can worsen quickly (approx. 1-2 weeks) if the weather promotes disease development on susceptible hosts.
We recommend treating with fungicide to manage the disease. Three fungicides are labeled for use on sunflower rust (Folicur, Headline, and Quadris).
For more information on disease and treatment recommendations, please go to: