When stalk rot occurs late in the season, it may have little or no direct effect on yield, according to OSU Extension specialists Pierce Paul and Peter Thomison. However, stalk lodging, which results from stalk rot, can have such a significant impact on harvest losses.
Several factors may contribute to stalk rot and lodging, including extreme weather conditions, insects and diseases, and these may occur very early in the season, write the OSU agronomists in a recent issue of C.O.R.N. newsletter. However, most hybrids do not begin to show stalk rot symptoms until shortly before physiological maturity.
"It is difficult to distinguish between stalk rots caused by different fungi because two or more fungi may be involved," the agronomists say. "Similarly, certain insects such as European corn borer often act in concert with fungal pathogens to cause stalk rot. Although a number of different fungal pathogens cause stalk rots, the three most important in Ohio are Gibberella, Collectotrichum (anthracnose), and Fusarium."
The presence of stalk rots in corn may not always result in stalk lodging, especially if the affected crop is harvest promptly.
"It's not uncommon to walk corn fields where nearly every plant is upright yet nearly every plant is also showing stalk rot symptoms!" according to the authors. "Many hybrids have excellent rind strength, which contributes to plant standability even when the internal plant tissue has rotted or started to rot. However, strong rinds will not prevent lodging if harvest is delayed and the crop is subjected to weathering, e.g. strong winds and heavy rains."
A symptom common to all stalk rots is the deterioration of the inner stalk tissues
To test stalk tissue Paul and Thomison suggest squeezing the stalk between thumb and finger. It is possible by using this "squeeze test" to assess potential lodging if harvesting is not done promptly. The "push" test is another way to predict lodging. Push the stalks at the ear level, 6 to 8 inches from the vertical. If the stalk breaks between the ear and the lowest node, stalk rot is usually present. To minimize stalk rot damage, harvest promptly after physiological maturity. Harvest delays will increase the risk of stalk lodging and grain yield losses, and slow the harvest operation
For more details and pictures of the disease symptoms associated with these pathogens. For more information on stalk rot in corn, consult the OSU Plant Pathology web site "Ohio Field Crop Diseases"