MONMOUTH, Ill. — Take a cold, wet spring and flooded soils. Add corn seeds planted hurriedly into soaked soils. Add some more rain. Wait a few weeks, maybe a month or two. Then repeat.

That cooks up the perfect recipe for a variety of corn diseases in the 2019 corn crop — and an added worry for a crop and farmers that already have endured a lot this year.

“This crop has been through a lot, and the year is only half over with,” said Jim Donnelly, Asgrow DeKalb technical agronomist.

Donnelly’s territory covers northern Illinois, primarily regions from I-80 and north.

Rachel Willis, Asgrow DeKalb technology development rep in west-central Illinois, joined up with Donnelly at the Bayer Learning Center in Monmouth to talk about current disease issues in corn and soybeans.

Gray leaf spot is the primary disease that farmers need to be on the lookout for in the corn crop. But a disease that traditionally is more of a concern in the southern part of the growing area, from southern and central Illinois to southern Indiana, could be making a move north.

Gray leaf spot starts out as small gray lesions that grow into long, blocky lesions that follow the leaf vein.

Willis showed leaves she picked from the Bayer Learning Center cornfields that exhibited signs of the disease.

“When I start seeing gray leaf spot this farm up the canopy, just at tassel, that’s a very good sign that we’ve had very good conditions for gray leaf spot and there’s quite a bit of inoculum out there,” Willis said.

Donnelly noted that signs of the disease on the lower leaves indicate that the disease is on the move toward the upper part of the stalk.

“Based on what’s happening down here and how fast it’s moving up, that really can be an indicator of what’s going to happen in the latter part of the season. Remember, we still have the whole second half of the season to go, so there’s a lot of time for all this stuff to become infected,” Donnelly said.

Donnelly pointed out that even if it hasn’t rained in an area, there still is enough moisture in fields for gray leaf spot to progress.

“You don’t need rain to continue disease progress. All it needs is free water, free water sitting on leaves and whorls, to be able to continue to spread,” Donnelly said.

Southern Rust

On another disease front, a disease commonly found in the southern United States may be moving north.

Following Hurricane Barry, even though it was short-lived, southern rust is something that farmers should be scouting for even in the northern parts of the growing area. What makes the 2019 corn crop particularly susceptible is the amount of later and late-planted corn.

“If that moves in soon enough, especially on later planted corn, it can cause yield loss there. The reason it can be important this year is because we have a lot of later planted corn, so all of that is going to be more susceptible to southern rust injury if we were to get it here at a pretty decent time,” Donnelly said.

Willis said that southern rust spores can look like physoderma brown spot. But there is one important difference that farmers can use to quickly determine the disease.

“Physoderma is a fungi that affects early season corn. It can cause very small orange spots that can look like southern rust. You can’t rub this off. If it was southern rust, my finger would be bright orange. If you can’t rub it off, it’s not southern rust,” Willis said.

Jeannine Otto can be reached at 815-223-2558, ext. 211, or jotto@agrinews-pubs.com. Follow her on Twitter at: @AgNews_Otto.

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