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The Next Month Will Be Critical for Disease Development

Recent cold, wet conditions are favorable for seedling diseases in early planted corn.

Recent cold, wet field conditions and fluctuations in soil temperatures have put early-planted corn at risk for seedling disease, and there may be considerations for replant in some areas.

“It’s been a mixed bag across the country,” says Randy Hagen, knowledge transfer manager at Monsanto.

“Cold soil temperatures and episodes of recent rainfall are especially favorable for some of the most common and damaging seedling diseases favored by cold wet conditions,” says Tamra Jackson-Ziems, University of Nebraska (U of N) Extension plant pathologist in a U of N Cropwatch article. “Numerous seedling diseases can take advantage of any of these conditions.”

Monitor seedling emergence and stand establishment in the coming weeks so diseases can be detected early.  

Seedling diseases can be caused by any of several common soilborne organisms, such as Pythium, Fusarium, Rhizoctonia, or parasitic nematodes. To complicate things, seedling diseases can be confused with insect injury, herbicide damage, planting problems, or environmental stresses that often have similar symptoms, says Jackson-Ziems.

Look for these symptoms of seedling diseases:

  • Rotted seed prior to germination   
  • Rotted or discolored seedlings after germination prior to emergence
  • Postemergence seedling damping off 
  • Root or hypocotyl decay

At least 14 species of Pythium have been identified that can cause seedling blight and root rot. These pathogens require excessive moisture, says Jackson-Ziems.

“The pathogen overwinters in soil and infected plant debris by producing thick-walled oospores that can survive for several years in the absence of a suitable host and favorable weather conditions. In addition to wet soil conditions, some species of Pythium are favored by cold soil conditions and are most likely to cause seed and seedling diseases lately,” says Jackson-Ziems.

At least six Fusarium species can cause seedling diseases and root rots. Stressed plants due to weather extremes (temperature and moisture), herbicide damage, and physical injury are more prone to infection and disease caused by Fusarium species, says Jackson-Ziems.

“Rhizoctonia species can also cause seedling diseases, but tend to be more common in drier growing conditions,” says Jackson-Ziems. “Rhizoctonia tends to cause reddish-brown lesions that can girdle and rot off roots. Root and crown rot may be severe enough to cause seedling death.”

Management

The most common method for disease management is the use of seed treatment fungicides.

In general, corn has protection from early disease because it’s been treated, says Hagen. Most seed corn is already treated with more than one seed treatment fungicide, often an insecticide, and, sometimes with a nematicide.

These products can provide protection against some of the pathogens that cause seedling diseases; however, they only provide protection during the first few weeks immediately after planting.

Scout fields

Diseases may still develop due to extended periods of inclement weather or if they are under severe pathogen pressure, says Jackson-Ziems.

The next month or so will be critical, says Hagen. “Look at field history, what has happened in your area, and what conditions are present today,” he says.

He recommends knowing what potential disease exists in your field. “Don’t wait until the last minute,” says Hagen. “Check your fields regularly, and ask your agronomist a lot of questions. Being aware is an important management tool in today’s world.”

Pay additional attention to areas that had standing water, warns Hagen. In places with a lot of standing water, there’s a higher risk of disease.

“If it is cold and wet, pay attention to that,” he says. “Those are potential signs for future diseases. But if it gets hotter and drier during the summer, that will go away.”

For some of those diseases, there’s nothing you can do, says Hagen. But knowing that history will help your to make management decisions next year.

If you’re considering replant, don’t make a snap decision. “Wait on replant until it’s a time where it makes sense,” says Hagen.

So far, replant has been minimal throughout the Midwest, says Hagen. But if you’re in a situation where replanting is a consideration, remember these steps:

  1. Evaluate the stand in several areas throughout the field.
  2. Consider the soil type. Soil type is key to understanding if there’s a chance for crusting and compaction, says Hagen.
  3. Check the herbicide history.
  4. Consider the time of year. If it gets too late, you may need to switch maturities to an earlier product. But until it gets later, you may not want to change the maturity.
  5. Factor in early frost dates.
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