How Can Stalk Rots Influence Your Harvest Schedule?

All corn producers know the problems related to stalk rots.

When corn stalk integrity is compromised, many issues emerge, such as:

  • Yield loss from premature death of the corn plant, due to the shortened kernel fill period

  • Harvest difficulty and ear loss due to stalk lodging from cannibalized stalks

  • Constant machine adjustment during harvest to separate the light kernels from other material

  • Secondary infections, such as ear rots

  • Additional drying costs, due to harvesting at higher moisture 

  • Storage risks due to molds and insect damage 

These problems can be reduced if corn is treated with a fungicide at or after VT. However, extreme air temperatures (higher than 86 degrees and lower than 50 degrees) can favor disease development, even if fungicides are applied.

Knowing the Cause of Stalk Rots

There are several fungi that cause stalk rot:

  • Anthracnose stalk rot can be identified by black lesions on the outside of the corn stalk. Cloudy weather favors anthracnose development. 

  • Gibberella is identified by a pinkish pith inside the corn stalk and flourishes in wet, warm environments after silking. It can be seen as pepper spots on the stalk.

  • Fusarium also shows as a pink pith and does well in warm, wet weather. It displays as a white powder on the corn stalks. Both Gibberella and Fusarium can lead to ear rots. 

  • Diplodia stalk rot can be identified as small brown specks on husks and ears. 

  • Charcoal stalk rot dries the pith of the stalks and produces sclerocia that compares to charcoal dust. Charcoal stalk is usually the cause of premature death of corn plants. 

  • Bacterial stalk rot appears as brown, water-soaked lesions accompanied by slimy roots. 

Temperature, moisture stress, genetics and fertility are all factors that can influence stalk rot establishment. Rather than identifying which stalk rot fungi is present, knowing where it is present can be more important for making harvest management decisions.

Scouting for Stalk Rots 

As the corn crop begins to show signs of maturity, it is a good time to begin scouting for stalk rot presence. This scouting should be done on a weekly basis until harvest. Examine each field in several locations by pinching stalks 1 to 2 nodes from the ground on 10 consecutive plants. If the pinch causes the stalk to collapse, it likely has some sort of stalk rot. Take time to split the stalk open and examine the internal contents. If the pithy area of the stalk has shrunk or become discolored, stalk rot is evident. 

Another method of determining stalk rot incidence is to push corn plants to approximately to a 45 degree angle from the upright position. Select several locations, using 10 to 20 consecutive plants. Plants that collapse from the pushing are probable stalk rot victims. If 10 percent to 15 percent of plants indicate stalk rot presence - from either scouting method - early harvest should be considered. Target fields of highest stalk rot incidence for the first to be harvested.

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