Stalk Rots of Corn
Stalk Rots of Corn
Symptoms
Symptoms of stalk rots are frequently first noted on early maturing varieties and on corn stalks producing two ears. Some surface discoloration, especially around the nodes, may be noted.
Distinguishing characteristics of the four most common stalk rots in Kentucky are as follows:
Stenocarpella (Diplodia) stalk rot - (Stenocarpella (Diplodia) maydis). This disease appears several weeks after silking when affected plants die suddenly; the symptoms resemble frost injury. The lower stalk is spongy and light to dark brown. Small dark-brown to black spots (pycnidia) may develop just below the stalk epidermis near the nodes. Upon splitting the stalk, disintegrated brownish pith is encountered.
Gibberella stalk rot - (Gibberella zeae). Leaves suddenly turn dull, grayish-green and lower internodes soften and turn tan or brown. Small superficial black spots (perithecia) of the fungus may at times be seen on the stalk. The stalk interior frequently shows a pink to reddish discoloration and shredded pith. The pink discoloration and superficial perithecia, which may be easily dislodged by rubbing a fingernail over them, distinguish Gibberella from Stenocarpella (=Diplodia) stalk rot.
Fusarium stalk rot - (Fusarium moniliforme). Roots are often rotted. The pith is whitish-pink to salmon-colored. As a consequence, Fusarium stalk rot is difficult to distinguish from Gibberella stalk rot.
Charcoal Rot - (Macrophomina phaseolina). Charcoal rot begins as a root infection, spreads into the lower stalk internodes and causes early ripening, shredding and breaking at the crown. The very tiny black fungal bodies (sclerotia) on the vascular strands of the shredded pith give the interior of the stalks a charred appearance (hence the name) and are a characteristic sign of this disease.
Anthracnose lower stalk rot (Colletotrichum graminicola). The exterior nodes and internodes of the corn stalks show a dark discoloration. Occasionally dark spines can be seen in these darkened areas with the aid of a hand lens. Interior shredding of stalk pith is also common. In addition to lower stalk rot, anthracnose also produces a top-dieback symptom on susceptible hybrids.
Causes
The development of stalk rots in corn depends on a number of factors including: unbalanced fertility, low potassium (K), poor soil drainage, mechanical and/or insect damage, foliar diseases, corn variety, excessive plant density and inadequate row spacing.
In Kentucky, late season stalk rot is commonly caused by one of five fungi: Stenocarpella (Diplodia), Gibberella, Macrophomina, Fusarium, or Colletotrichum.
IPM Techniques
- Examine the field once at harvest maturity before crop is harvested.
- When scouting for stalk rot, examine 20 stalks in each of five sites per field.
- Check for stalk rot by either of the following methods:
- Squeeze the base of the stalk with your hand or
- At about chest height, push the stalk 8 to 10 inches from its vertical position to check for lodging.
- Note the type of stalk rot and the number of plants showing symptoms. Some plants may have more than one type of stalk rot present. If so, record all the types present.
- A field should be scheduled for early harvest if 10-15% of the plants are showing stalk rot.
- If harvesting early, be sure to dry grain quickly to prevent ear and kernel rots.
- To minimize stalk rot in the future, plant resistant varieties and hybrids.
References and Additional Information
- IPM-2 Kentucky Corn IPM Manual
- PPA-10a Kentucky Plant Disease Management Guide for Corn and Sorghum, P. Vincelli and D.E. Hershman, Extension Plant Pathology, University of Kentucky
- PPA-26 Corn Stalk Rots, R.E. Stuckey and D.E. Hershman, Extension Plant Pathology, University of Kentucky
Compendium of Corn Diseases. M.C. Shurtleff. American Phytopathological Society. 1980.
