Stalk rot is present to some extent in every Iowa corn field at harvest time. The decay of corn stalks after physiological maturity is a natural process of recycling nutrients and organic matter. However, stalk rot is considered a disease problem when it occurs prior to physiological maturity, resulting in premature death of plants and yield loss due to poorly-filled kernels. Also, stalk rot developing after maturity, but before harvest, will cause lodging, resulting in an inability to harvest the ears.
Stalk rot is caused by an interaction between soil- or residue-borne fungi and environmental stresses acting on the plant. Any conditions that reduce photosynthesis and the production of sugars can predispose the plant to fungal infection and severe stalk rot. Such stresses include leaf diseases, hail damage, crowding of plants, drought, soil saturation, lack of sunlight, extended cool weather, low potassium levels, numerous weeds, and insect damage. Stalk rot occurs because stresses prevent the plant from producing enough carbohydrates to fill the grain and maintain healthy root and stalk tissue.
Several different fungi can cause stalk rot, and they often occur in combination. Stalk rot pathogens are present in every corn field; however, the distribution and severity of stalk rot depends more on plant stress than on the distribution of the pathogens.
Course of Infection
The fungi usually enter plants through their roots, and root rot almost always precedes stalk rot.
Premature death of the plant results from destruction of the water-conducting tissues of the roots and lower stalk.
Eventually all that is left of the stalk are the vascular bundles and outer rind composed of thick-walled cells that are less likely to decay.