Don’t let downy mildew take down your sunflower field
Downy mildew resurfaces every year, but not always in the same locations, Markell added. Depending on environmental conditions, fields of all sunflower growers, particularly in northern states, are at risk of contracting the disease.
Despite the potentially devastating effects of downy mildew, there are management options for controlling the disease before it destroys yield.
Monitor fields and pinpoint prone areas
Each year, growers should assess their risk for downy mildew by monitoring their fields, identifying low-lying areas and observing environmental conditions like cool temperatures and prolonged rainfall. If growers feel at-risk, they can plant sunflower hybrids that are tolerant against downy mildew, including nine Syngenta sunflower seed hybrids. However, genetic tolerance levels vary and may not provide protection in severe downy mildew infestations.
“Growers should determine their risk for downy mildew because there are areas that will be infected year after year,” Markell said. “For the growers whose fields are more susceptible, varieties with genetic resistance are very important. The infection can happen quickly, and it only needs to happen once.”
The pathogen stays with its sunflower host until it reaches maturity when it forms an overwintering structure, which allows downy mildew to stay in soils for up to a decade. Unfortunately, cultural practices like crop rotation won’t mitigate the disease out of infected soil.
“Although crop rotation has a minimal effect on downy mildew management, growers can work to control volunteer or wild sunflowers near their fields,” said Tom Schmit, South Dakota-based agronomic service representative at Syngenta. “These unwanted plants can provide a host for downy mildew.”
In addition to planting tolerant varieties and eliminating volunteer sunflowers, growers can proactively protect against downy mildew by applying seed treatments before planting.
Treat your seed right
By applying a seed treatment fungicide, growers can prepare for downy mildew infections before the season even starts. In fact, a fungicide seed treatment is the only effective crop protection product for downy mildew control, providing additional protection for less tolerant hybrids and areas most at-risk for the disease. “Foliar fungicide applications may prevent other diseases, but they won’t protect crops from downy mildew,” Schmit explained.
“Sunflowers that have been treated with certain fungicides are much better poised to fend off downy mildew than untreated seed,” Markell said. “I recommend that sunflower growers apply seed treatments for protection from downy mildew and other pests,” advising that growers should be proactive rather than learn the hard way.