Figure 15. Stalk rot diseases result in poor quality grain and yield loss from unharvestable ears due to severe lodging. Several different stalk rot diseases occur in Ohio.
Stalk rots are undoubtedly the most common corn diseases in Ohio (Figure 15). A number of fungi cause stalk rots. The most important in Ohio are caused by Gibberella (Figure 16), Colletotrichum (anthracnose) (Figure 17), Diplodia (Figure 18), and sometimes Fusarium. When stalk rot occurs late in the season after complete denting of kernels, it usually has no direct effect on yield. Certain stalk rots, like anthracnose and Gibberella, can cause premature death of plants and impact yield directly. However, the lodging of diseased corn plants has such an impact on harvest losses that many consider stalk rots to be the most significant yield-limiting diseases of corn. Fields with severe stalk rot should be harvested as early as possible.
The severity of stalk rot is confounded by plant stress. In general, the greater the stress the plant endures, the greater the severity of stalk rot. This has been demonstrated very well with plant nutrition. Plants with excessively high levels of nitrogen or with an imbalance between nitrogen and potassium are very susceptible to stalk rot. Plants stressed by drought (especially late season drought), foliage disease, or insect injury generally have more stalk rot. Stresses that affect the ability of the plant to produce sugars in leaf tissue and move sugars to the ear for kernel fill or to lower stalks to keep them alive tend to impact the level of stalk rot in the field. Corn growers should follow an integrated approach to manage stalk rot diseases. Management is based on avoiding or lessening stress on the plants. Follow as many management practices for disease control, outlined later, as feasible, depending on the equipment available and feed needs of your operation.
 Figure 16. Giberella stalk rot is the most common cause of lodged corn in Ohio. Pink coloration and disintegration of pith tissue are characteristic symptoms of Gibberella stalk rot. Note the dark specks that are fungal spore-bearing bodies, located near stalk nodes. |
 Figure 17. Anthracnose stalk rot can be recognized at corn maturity as shiny black streaks, specks, or blotches on the stalk rind. Internal stalk tissues have a dark gray coloration and pith tissues are rotted. Stalks of highly susceptible hybrids may turn entirely black. |
 Figure 18. Diplodia stalk rot is identified by having brown dis-colored nodes and very small black fungal bodies scattered over the internode surface. Diplodia stalk rot is more common in fields planted to continuous corn. |
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