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Consider stalk rot and weed pressure this fall

By Staff | Oct 6, 2017

-Submitted photo by Angie Rieck-Hinz EVALUATING FOR STALK rot using the push test shows 4 in 10 plants were impacted by stalk rot and this field should be prioritized for early harvest.



Harvest can mean more than bringing in this year’s crop.

It can be an opportunity for growers to evaluate all that was good, and also all that was bad with this year’s growing season.

Angie Rieck-Hinz, Iowa State University Extension field agronomist, said it is important for producers to be keeping an eye out for any standability issues in corn – figure out what has caused that to be proactive for next year and, she said, to be aware of weed pressure and the areas where weeds escaped the canopy this year to help plan for better weed control for next year.

Stalk rot

Rieck-Hinz said stalk rot has been found in many acres of Iowa’s corn fields this year.

“We do have plenty of stalk rot in places,” she said. “We have anthracnose stalk rot and charcoal stalk rot, which seem to be the two most prevalent stalk rots this year.”

She said there are about five to six different kinds of stalk rot that can affect corn. It’s usually caused by different fungi, with some caused by bacteria, but that is very rare.

“We shouldn’t be too surprised about some of our stalk rots this year,” she said, adding that it seems like charcoal stalk rot is being seen in more fields, “where it’s been stressed because it was hot and dry in the growing season.”

Although producers should have been checking their corn crop for stalk strength and any standability issues long before now, Rieck-Hinz said it’s not too late.

“When we go out to evaluate a field, about the time it gets to physiological maturity – when we get to the black layer – we should be out assessing for standability and stalk strength at that time,” she said, adding there are two ways to test for stalk rot: the pinch test and the push test.

The pinch test is done by testing the stalk’s firmness by pinching the lower internodes with your thumb and forefinger. Healthy stalks, according to Rieck-Hinz, are firm and cannot be compressed. If a stalk can be compressed or feels soft, it is rotted and is a good candidate for lodging.

The push test is done by pushing stalks over, at ear level, eight to 12-inches or so to make the plant about 30 degrees from vertical. If the stalks pinch and fall over or fail to return to vertical, stalk rot is a problem.

Rieck-Hinz said she will assess 100 different plants in two to three different places in the field.

“If 10 percent of those stalks fail in that field, we want to really consider prioritizing that field for sooner harvest because the standability will be an issue,” she said, “in particular if we get a windy day like we tend to in the fall, or if we go in to a wet period.”

“It may pay to move up harvest in that field,” Rieck-Hinz added. “Even if moisture isn’t where we want it to be for harvest, it might actually reduce harvest losses by harvesting it sooner.”

Making that field a priority could also help save time.

“We don’t get into lodging, we don’t get into down corn where we increase harvested losses. That will also increase harvest time,” Rieck-Hinz said. “It takes a lot longer to harvest corn that has gone down.”

She advised to take the time and do those stalk tests now.

“People should be out doing that right now,” she said. “There’s still a lot of corn still standing, so it is still a good time to get out there and look at those things.”

Management for

stalk rot

At this point, Rieck-Hinz said there isn’t much that can be done with those corn plants that may be affected by stalk rot. However, it can be time to figure out just what has happened to the plant and what can potentially be done for next year.

“We can choose hybrids that have been adapted, that are more tolerant or resistant to certain diseases, so we can think about that this time of year while going through the field in the combine,” she said. “What do we think is happening out there? How could I change my management plan for next year? Do I need a hybrid with a stronger rating?”

Rieck-Hinz said it may be necessary to find exactly what kind of stalk rot was affecting the corn. This can be done by sending samples to the ISU plant disease clinic or a commercial lab.

“Certainly if you’re seeing some traits and consistent issues across the same hybrid or in multiple fields or areas, maybe you should have it positively identified and then make management decisions based for next year,” she said.

Rieck-Hinz said when it comes to the hot, dry weather conditions from this year, some corn plants are suffering from damage caused by plant cannibalization, which then has made the plant more susceptible to stalk rot. Plant cannibalization, she said, is caused by the plant using its own nutrients to help make grain fill further, causing the stalk to potentially rot and fall apart sooner than it should have.

In addition to getting out into the field and testing for stalk rot, she recommends keeping a close eye on things while in the combine.

“Combine time is important,” Rieck-Hinz said. “One of the things we can do is look at how that plant is still standing and see how it performs under dry conditions, wet conditions, diseases and those kinds of things.”


Looking through the windshield of the combine, Rieck-Hinz said, should give a good perspective just what weed control did, or possibly did not do, this year.

“If we have weeds above the corn or soybean canopy, we didn’t have effective weed control,” she said. “Identify those parts of the field and we need to ask ourselves what happened.”

Rieck-Hinz said things to consider when it comes to trying to solve why herbicides may not have worked could be:

-Were the plants under stress? Such as in soybeans; were they shorter, or thinner, and didn’t canopy so more weeds were able to pop through due to the lack of competition?

– Were the weeds already too big when the post-emergent herbicides were applied?

– What was the weather like when those applications were done? Was it hot? If so, she said in those cases, weeds could have hardened off and didn’t absorb the herbicides.

“Think back about those kinds of things,” she said. “We need to be thinking of that now when we see weeds patches in the field. We really shouldn’t have weeds poking up through the canopy in my opinion. We should have better weeds control than that.”

Rieck-Hinz said producers, especially those with no-till operations, also need to think about what kinds of winter annual weeds they have.

“What kinds of winter annuals we have and can we manage those winter annuals with a herbicide application this fall, so they are not as much of a problem next spring,”she said.

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