Don’t let downy mildew take down your sunflower field
With the ability to wipe out large portions of sunflower crops and significantly decrease yield, growers know that downy mildew is one of the most devastating diseases to strike sunflower fields. A soilborne pathogen that travels via water with “swimming” spores, downy mildew can be costly for growers. However, by monitoring and proactively employing the right cultural and chemical management practices, growers can manage the disease and preserve yield.
Downy mildew: know the enemy
Downy mildew can occur in all sunflower-producing regions of the U.S. and is most common early in the season, right after planting. The disease spores enter the roots of sunflower and systemically invade the rest of the plant, causing severe stunting and oftentimes killing plants.
“Downy mildew is a very important disease in sunflowers because of the potential damage it can cause,” said Sam Markell, plant pathologist with North Dakota State University Extension. “An infection from this unusual pathogen can result in 100 percent yield loss to the infected plants.”
If infected plants are able to survive, they develop thick, yellow leaves and a white cotton-like substance appears on their undersides. According to Markell, if sunflower growers see these symptoms in their fields, it’s probably beyond the point of control.
“There is a lag time between the moment of infection and when downy mildew symptoms start to show on sunflower crops,” he said. “By the time growers see symptoms, it’s already too late. Downy mildew cannot be managed after it occurs.”
Favoring cool, wet conditions, downy mildew is most prevalent in low-lying areas of sunflower fields with poor drainage, where water can pool and downy mildew spores can freely travel and infect large groups of plants. If infections in a field are spotty and only affect a few plants, resulting yield loss is minimal since healthy sunflowers have the ability to compensate for infected neighboring plants. However, Markell said downy mildew commonly infects large patches of sunflower fields at a time.
“Big patches of downy mildew result in very significant yield loss, which is what we tend to see much of the time,” he said, adding that secondary infections of the disease can also occur, but its effects are starkly different than a primary infection. “We are most concerned about the primary systemic infection. Secondary infections of downy mildew will result in spots on foliage, but that’s about it. Secondary infections of downy mildew will not damage plants or affect yields.”