University experts are reporting increasing disease pressure in corn fields throughout the country. Dr. Kiersten Wise, an extension associate professor at the University of Kentucky, and Dr. Alison Robertson, an extension field pathologist professor at Iowa State University, share the latest news on what they are seeing in across the country.
Southern Disease Pressure
“In our scouting right now, we’re seeing gray leaf spot ranging in severity from very light to moderate or severe levels in susceptible hybrids,” reports Wise. “We have a lot of reduced tillage and no-till in Kentucky, so there are a lot of fields with corn residue, and that’s where the fungus survives.”
Gray leaf spot thrives in warm, humid conditions, according to Wise. “We also see this disease in fields close to streams or riverbeds, where the humidity levels are higher. But just because a field isn’t in a river bottom doesn’t mean you won’t see gray leaf spot – we’ve had a lot of humidity this year in Kentucky, so we’re really seeing this disease take off in the later growing stages.”
There are other diseases lurking in Kentucky corn fields, according to Wise. “We’re looking out for diplodia leaf streak. It’s a fungal disease that causes long lesions that you can see in the canopy, so it can be confused with Northern corn leaf blight. We’re also starting to see diplodia ear rot. It affects the corn in the early to brown silk stages, but you don’t see symptoms until now. Symptoms include bleached husks and a white fungal matte on the cob.”
Ag retailers, agronomists and consultants can help growers minimize yield loss by scouting fields and making sure growers identify diseases correctly and evaluate options, Wise says.
Northern Disease Pressure
“It’s been extremely wet in parts of Iowa,” says Robertson. “We have some areas where we’re 200 to 300 percent ahead of normal precipitation levels for this time of year, so that provides great conditions for diseases to thrive.”
“We’re getting reports of physoderma bacterial leaf streak and physoderma brown spot in those areas that have been really wet,” she explains. “On the other hand, in southeastern Iowa where it’s been dry, we’re getting reports of gray leaf spot. In more susceptible hybrids, lesions can be all the way up to the ear leaf and those fields probably need a fungicide application.”
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