Since harvest kicked off this fall in Nebraska, many corn growers have encountered the telltale signs of stalk and crown rot: early discoloration of corn plants changing from green to brown, and hollowed-out plants in the top half or the entire plant — all signs the plant died off early. This includes stalk rots like anthracnose stalk rot, fusarium stalk rot and, in some drought-stressed areas, even charcoal stalk rot.

WATCH FOR STALK ROT: The tops of corn plants that have anthracnose stalk rot may break off before harvest, but this is not always an indicator of stalk and crown rot lower on the plant. (Photos: Tamra Jackson-Ziems)

"There is so much stalk rot out there right now," says Tamra Jackson-Ziems, Nebraska Extension plant pathologist. "A lot of producers are in a predicament because they have stalk rot and need to harvest corn quickly before it lodges. But in some areas, corn is not drying down very quickly. In places where moisture is still high, growers don't want to harvest early, so it's a really hard decision right now."

Which fields should you watch for stalk rots in? The best way to know if you have stalk rot in a cornfield is to walk through the field and use the push test or pinch test to evaluate stalk strength.

Jackson-Ziems notes any fields that experienced stress throughout the growing season are candidates for stalk rots. And this year especially, it could be any field. With sporadic rainfall in late April and May, followed by a hot, dry period in June, many fields in Nebraska experienced nutrient deficiencies, foliar diseases like gray leaf spot or southern rust, or water stress — either from too much, or too little water.

GRAIN QUALITY CONCERNS: The most common ear rots identified so far in Nebraska have been diplodia, fusarium (pictured here) and penicillium.

"Those are the fields I would certainly want to monitor," she says. "Some of the fields that were impacted by very heavy rainfall and had standing water a few days are definitely at higher risk as well as ones with drought injury, any of those stresses during the growing season can lead to stalk rots disease now."

Be mindful of ear rots when storing grain
In addition to stalk rots, growers may have noticed symptoms of ear rot in some cornfields during harvest. And Jackson-Ziems says growers need to know the extent of the problem. Ear rots could be caused by any kind of wound on the corn plant — including damage from western bean cutworm or hail damage, which affected some acres in Nebraska this year.

The most common ear rots identified so far  in Nebraska have been diplodia ear rot, fusarium ear rot and penicillium ear rot. So far, there has been no confirmation of aspergillus ear rot or any kind of mycotoxins in corn. The biggest concern from these ear rots is managing grain quality this winter.

"If growers store any affected grain from fields that had ear rot, those fungi can and will continue to grow in the bin if moisture is above 15%," says Jackson-Ziems. "We usually recommend growers dry and cool it as quick as they can, but that's not always very practical. If they know they have an ear rot problem, it would be best not to store grain at all. It would be best to have moisture less than 13% to store it, and those are near impossible conditions to get right now."

It's also important to cool the grain using an aeration system, even under normal grain storage considerations. "We would continue to make that recommendation for corn that has been infested, but it becomes more important because of the potential for deterioration to occur," adds Ken Hellevang, North Dakota State University Extension engineer.

The temperature to cool to varies depending on location, but the rule of thumb is that for every 10 degrees the stored corn's temperature is reduced, the allowable storage time is doubled. One reason to cool is insect activity — at temperatures under 50 degrees F, insects typically go dormant. Then there's moisture migration. Anytime there's a roughly 20-degree temperature variation in the grain mass, it creates a convection current in the bin, which typically causes moisture accumulation near the top of the bin where temperatures are cooler.

And the ideal target temperature depends on the region. For example, in North Dakota, on the single-digit-degree days of January, it's recommended to cool the grain down to at least 30 degrees to keep it within a 20-degree temperature difference. "In Nebraska, you don't have to cool it as much to minimize that moisture migration. But a temperature under 40 degrees is the target that's set," says Hellevang. "We try to keep it at that temperature as long as we can going through the winter and through the spring months."

In addition, when grain is affected by ear rot, there will likely be a shorter storage life, and it's a good idea to consider how long you're going to be storing that grain, adds Hellevang,

"If we have grain that has been infested, even though we have dried it down and are using the best storage management practices, we should probably keep in mind that this is corn that may not store well going through the next summer," Hellevang says. "Typically, we can store corn through the winter, going into the spring with very few problems, but once we get into warmer temperatures of spring and summer, then it becomes more difficult to manage the grain and maintain the corn quality."

Of course, when it comes to managing infected grain, Hellevang notes it's important to have a "safety first" mentality. "So we strongly recommend for anyone working around this grain that has molds associated with it, that they wear respiratory protection," says Hellevang. "The degree of respiratory protection will depend a little bit on the quantity of molds they might be exposed to and their sensitivity to it. In general, we recommend they wear a mask that carries an N95 or N99 rating, an indication that it's going to filter out most of the fine particulate matter, which the mold spores are."

Growers with questions on stalk rots or ear rots can contact Jackson-Ziems at [email protected].