Fungus Among Us

Wet Weather Spurs Disease

Illinois farmer Adam Watson examines northern corn leaf blight in his fields in 2014. Wet weather this June has allowed the disease to surface in corn fields once again this summer. (DTN photo by Emily Unglesbee)

IVESDALE, Ill. (DTN) -- Illinois farmer Adam Watson is playing the waiting game when it comes to corn disease this year.

Unrelenting rains across most of the Midwest have resulted in very early outbreaks of corn leaf diseases such as northern corn leaf blight, and Watson fully expects to see it surface in his fields soon. Yet current corn prices have placed preventative, farm-wide fungicide applications beyond his economic reach.

"If there was a year that I would expect to see [disease], it would be this one," said Watson, whose fields have seen a dozen inches of rain since he finished planting in early May. "But because of the price of corn, we're going to have to see disease show up before we can justify spraying."

State plant pathologists in Indiana, Iowa, Kentucky and Nebraska have issued alerts advising growers that northern corn leaf blight has already been found on the lower canopy of a few fields this year. Conditions are also good for diseases like gray leaf spot and scouting will be more important than ever in the coming weeks.

During an AgriGold Specialty Conference on Thursday, June 25, a panel of agronomists urged proactive scouting, particularly in fields planted to susceptible hybrids.

"This is the earliest we've seen it [NCLB] show up," said Todd Steinacher, an AgriGold regional agronomist covering central and western Illinois.

Given lower commodity prices, growers were hoping to dodge additional input costs this summer, but Steinacher said preserving yield may depend on a timely fungicide application.


NCLB is caused by the fungus Exserohilum turcicum and is characterized by long, tan, cigar-shaped lesions on leaves.

Scouting fields with lower disease ratings is at the top of his to-do list this summer, Watson said. "We're going to be looking at the hybrids that have weakest disease package first," he explained. "Then we'll keep an eye on other fields and see what happens."

In a university release, Iowa State plant pathologist Alison Robertson ticked off the ingredients for a justified fungicide application for northern corn leaf blight: "If the disease is present on 50% or more of the plants in the field, the hybrid is scored susceptible and cool, wet weather is forecast, a foliar fungicide application may be required," she wrote.

Crop price, crop condition, planting date and predicted weather conditions should all factor into deciding an economic return, added Kiersten Wise, Purdue University plant pathologist, in a recent news release.

It can be tempting to spray fields early when the disease is present, but research in Indiana indicates fungicides are most effective at preventing yield loss due to NCLB when applied at the tasseling to early silking (VT-R1) growth stage, Wise explained.

Early fungicide applications might help bolster the health of stressed or damaged corn, but they are unlikely to last through the growing season, and growers could require costly additional passes later in the summer, both Robertson and Wise pointed out.

Specifically, a V4 to V6 application of fungicide to corn will not protect the ear leaf or above from disease that develops around tasseling, Wise said.

"In 2014, applications at V5 to V6 reduced NCLB, but applications made at R1 were more effective at protecting the canopy through dent," Robertson added.

For Watson, this translates to a wait-and-see approach.

"We're going to be scouting very intensely for it just because of the economics of agriculture right now," he said. "It's harder to use a whole broadcast program on fungicides because of the cost."

Watson estimated a fungicide application would cost him $15 to $20 an acre, plus $10 an acre to pay for an airplane, now that his fields are too wet to use his high clearance sprayer.

"Just to pay for the airplane, you'd have to gain more than two bushels an acre," he pointed out.


As with most foliar diseases, Mother Nature will make the final call on how NCLB plays out this year, Robertson noted.

In 2014, a dry July slowed and even stopped NCLB development before it took off again in August through September when rainy weather returned to much of the Midwest. "If 2015 remains cool and wet, NCLB will win the 'Disease of the Year' award for a second consecutive year," Robertson predicted.

Unfortunately for north-central growers, the next month may well fit exactly that criteria, noted DTN Senior Ag Meteorologist Bryce Anderson.

"July is still looking cool for the season (near-below normal temperatures) and wet for the northern Corn Belt," he said. "In fact, we could see some periods of heavy rain in northern Iowa-southern Minnesota during the next three weeks."

His scouting trips haven't turned up any disease yet, but with his early planted corn fields beginning to tassel, and more rain in the forecast, Watson is on alert.

"What we may not see today may show up two weeks from now, so we're going to have to continue to scout as long as we're in the zone of being able to spray fungicides," he concluded.

Find fungicide recommendations and an efficacy table for management of corn disease developed by the National Corn Disease Working Group at:…

For more information on NCLB see this Purdue guide:…

See Robertson's university article on NCLB and corn disease this summer here:…

You can find Wise's recommendations on the risk and management of NCLB this year here:…

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