Figure 1. Symptoms of dark lesions on the leaf collar (left) and stalk (right) of corn (Photos by Tony Adesemoye)

In the last few weeks dark lesions on corn stalks and leaf collars have been noticed in many growers' fields, especially in west central Nebraska. The lesion color varies from purple to brown to black. These conditions were also seen in the university research farms. The condition is not specific to any hybrid, any part of the canopy, or any location in the field; instead, affected plants are scattered and random. Many of the plants showing symptoms were examined and it is a condition termed purple leaf sheath. Yeast, Alternaria (a fungus), and other organisms have been recovered from the symptoms, but they are not consistently associated with the condition and rather are saprophytes or secondary invaders.

These symptoms developed after the VT tasseling stage. As seen in Figure 1A (left), there were pieces of tassel that had fallen into the leaf collar in almost all situations where the symptoms were observed. The tassel and other debris that dropped to the leaf collar likely attracted many saprophytes. The subsequent interactions, including the plant's response, resulted in symptoms.

Potential Yield Impact

There is no indication that there will be significant negative effect on yield or that the condition spreads from one plant to the other. The plants that exhibited the symptoms produced stalks, leaves, cobs and kernels that were comparable to other stands in their immediate environment.

This condition is usually only cosmetic and of minor concern and would not warrant a fungicide treatment.

Tony Adesemoye
Extension Plant Pathologist, West Central REC