Figure 1. Downy mildew symptoms on sunflower seedling.
As is the case every year there is a possibility that we may see some downy mildew in young sunflower fields around the state in 2018. Downy mildew is often found at low levels in fields. Prevalence and incidence of this disease will vary from year to year as environmental conditions do impact the incidence of this disease. Cool, wet soil conditions and heavy dews are conducive to development of the disease.
Downy mildew of sunflowers is indigenous to South Dakota and is capable of infecting all wild sunflower species. This disease is soil borne and can survive for many years in the soil. Seedlings are only susceptible to the disease for a limited time early in their lifecycle. Wet, low areas in a field are often areas the disease can be found. In rare occurrences the disease can be seed borne. When this occurs, again rarely, the disease will impact a larger area of the field.
Planting genetically resistant hybrids and the use of fungicide seed treatments has been the most common method of managing this disease. However, some fungicide resistance (FRAC 4 chemistry) has been identified. Systemic infections, or infection of seedlings through the roots causes the most serious losses. Symptoms include stunting, leaf chlorosis, white sporulation on the underside of the leaf and eventually plant death. Mature plants will be stunted and heads will be horizontal at maturity. Secondary infections result in little to no yield loss and can be identified by discrete chlorotic leaf spots on upper leaf surface.
Dr. Febina Mathew, the field crops (research) pathologist at South Dakota State University is interested in receiving samples of downy mildew infected sunflower plants to study pathogen virulence and its impact on South Dakota’s sunflower crop. Contact Febina Mathew for more information or to submit diseased samples.
South Dakota State University
113 Plant Science Building (SPSB), Box 2108
Brookings, SD 57007