As corn harvest beings across the state, reports of stalk rot are coming in from some locations. Several factors may contribute to stalk rot, including extreme weather conditions, insects and diseases. Although it is often difficult to distinguish between stalk rots caused by these different factors, mid- to late-season northern corn leaf blight (NCLB) may have been the culprit this year. NCLB reached fairly high levels in some fields, particularly in those planted with susceptible hybrids. In some cases, leaves above the ear were affected and became blighted well before grain-fill was complete. When this happens, plants often translocate sugars from the stalk to fill grain, causing them to become weak and predisposed to fungal infection. A number of fungal pathogens cause stalk rot, but the three most important in Ohio are Gibberella, Collectotrichum (anthracnose), and Fusarium. For more information on stalk rot in corn, consult the OSU Plant Pathology web site "Ohio Field Crop Diseases" (http://www.oardc.ohio-state.edu/ohiofieldcropdisease/) for more details and pictures of the disease symptoms associated with these pathogens.
Losses due to stalk rot may vary from field to field and from one hybrid to another. Stalk rots may cause lodging, especially if the affected crop is not harvested promptly. However, it is not uncommon to walk corn fields where nearly every plant is upright yet nearly every plant is also showing stalk rot symptoms. 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 so that one or more of the inner nodes can easily be compressed when 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.