Harvest is drawing near, and I’m optimistic that we will see some great yields. I can’t help but think that we’ll also see more stalk rot and premature plant death due to wet planting conditions, severe storms throughout the growing season, and low rainfall periods in July.

We expect corn plants to begin maturing this time of year, but you may notice that some areas of fields are maturing more quickly. Other areas may even die early. When corn plants don’t live for the full season, they don’t achieve maximum potential yields. Even though the kernels on “prematurely dead plants” display a black layer, the lack of kernel size indicates they reached this stage too soon.

Why do plants and areas of the fields die prematurely this year? While every field is a little different, there is almost always more than one factor involved. Reasons for premature death that I have witnessed this year include: moisture stress, nitrogen loss, anthracnose top-dieback, stalk rot, and wind/hail damage.

Moisture Stress. Generally, corn root development was not good this year because of early season wetness over an extended period. During grain fill, a plant needs a lot of water. Shallow, poorly developed and partially decayed root systems can’t provide enough moisture to keep the plant going especially during hot summer days. This scenario is particularly noticeable in places where there was standing water earlier in the season.

Nitrogen loss.  Some plants are showing significant signs of nitrogen deficiency before they die. Wet conditions early in the season have resulted in the loss of nitrogen in many fields or parts of fields, and plants prematurely die because of a severe nitrogen deficiency.

Anthracnose top-dieback.  This phase of the anthracnose disease is less common than the typical stalk rot that occurs at the stalk base. With top-dieback, the plant dies from the top down. The upper leaves turn yellow or reddish purple, then dry out. The fungus usually infects through the whorl earlier in the season and remains dormant in the stalks until late in the season.  Late-season stress triggers the development of disease symptoms.

Sighting of a yellowed, or purple flag leaf on the corn plant is a key symptom of anthracnose top-dieback.  (above).  Another key sign will appear during wet conditions.  A pink substance will be observed on the stalk (below).  Photos courtesy of Iowa State University.

Stalk rot.  Some plants might die because the base of their stalk is rotted by Gibberella or Fusarium.  The onset of these stalk rots is also stress related. When the stalk base is rotted, the whole plant wilts and dies rather suddenly. To see the symptoms, you may need to split the stalk all the way up the base, from below the soil line.

Wind/hail damage.  Plants that were damaged by wind and hail earlier in the season are vulnerable to a number of problems that may show up now. Because of the physical damage to leaves, stalks, and roots, these plants are especially likely to suffer from stalk rot or a moisture-stress-related death.

To summarize, all of the stresses have likely contributed to the overall rapid shutdown of photosynthetic leaf area.  Given the importance of live, viable leaves and their contribution to the grain filling process, the rapid leaf senescence evident in corn fields this year will likely shave some bushels off the upper limit of yield.  Plants suffering from such stress struggle to complete grain fill before they die. As plants stuggle, they often resort to cannibalizing the carbohydrates and nutrients from the leaves and stalks in order to fill the grain.  This leads to root and stalk rots.

Obviously there is nothing that can be done now to prevent premature death.  However, growers should walk these fields during the next few weeks, monitor the stalk health, and adjust harvest strategies accordingly to manage fields where stalk lodging may be a big problem.