Stalk rots have emerged as a major issue as the 1997 season draws to a close. Anthracnose, Fusarium, and Gibberella stalk rots were very prevalent throughout the state, causing premature plant death and lodging. The early snow and periodic high winds have not helped the situation, as many weakened stalks have given out. Many producers are wondering what can be done to reduce the risk of stalk rots in the next corn crop, especially in terms of tillage practices.
Because stalk rots are the result of complex interactions among the plants, the pathogenic fungi, and the environment, each field has a different set of factors contributing to the problem. That means proper stalk rot management varies from field to field. Tillage may be appropriate in some fields but not in others.
The following are some common questions about the effects of tillage on stalk rots.
Does plowing or chiseling affect the occurrence of stalk rots? The answer is yes, but the effect can be positive or negative, depending on the individual field. Generally, tillage is not considered an effective way to reduce stalk rots. The pathogens survive in crop residue, which usually means that their survival can be reduced by tillage. However, in this case, the reduction in survival is not sufficient to have a great influence on disease occurrence. These fungi are present to some extent in every cornfield, and disease occurrence is influenced primarily by the environment and its effects on the corn hybrid.
Under what conditions can tillage increase stalk rot problems? Under some conditions, research has shown that plowed fields have a greater incidence of stalk rot than no-till fields. This can occur if rainfall is insufficient during the grain-fill period. Under low rainfall conditions, no-till soils will hold significantly more moisture than plowed fields. Plant stress caused by inadequate soil moisture makes the plants more susceptible to stalk rots.
Under what conditions can tillage reduce stalk rot problems? If the stalk rot was the indirect result of some other problem, tillage may be appropriate. The best example is severe leaf disease. When gray leaf spot is severe in a field, it is very common that stalk rot problems will follow. The stress on the plant, caused by the leaf disease, induces greater stalk rot susceptibility. In this case, the correct approach would be to manage the gray leaf spot problem, possibly by performing tillage. If the gray leaf spot is reduced, the stalk rot problem will be reduced. Another example is surface compaction. When the root system of a plant is badly restricted by compaction, stalk rots may follow. Again, the underlying problem may be improved through tillage.
A study conducted by pathologists at The Ohio State University illustrated the effect (or lack of effect) of tillage on stalk rot. From 1987 through 1995, they compared no-till with fall plowing treatments in continuous corn or in a corn-soybean rotation (Table 1). In four of the seven years, there was no effect of tillage on stalk rot. In the other three years, there was more stalk rot in the plowed treatment than in the no-till treatment. Surprisingly, crop rotation did not reduce stalk rot in this study. Yields, however, were significantly better in the corn-soybean rotation (Table 2).
Table 1. Effects of tillage and rotation on corn stalk rot in Ohio, 1987, 1988, and 1991-95 (Lipps and Deep, The Ohio State University).
|Percentage of plants with stalk rot|
a NS = effect was not statistically significant, + = tillage increased stalk rot
Table 2. Effects of rotation and tillage on corn yields in Ohio, 1987, 1988, and 1991-95 (Lipps and Deep, The Ohio State University).
a NS , effect was not statistically significant; +, tillage increased yield; -, tillage decreased yield
In this study, we can see the effect of soil moisture. The years in which no-till plots had significantly less stalk rot than plowed plots were dry years in Ohio (1988 and 1991). When growing conditions were very good and soil moisture was adequate but not excessive, stalk rots were minimal and yields were good (1994).
So what is the bottom line? The decision to perform tillage must be examined on a field-by-field basis, and must include many considerations other than stalk rots. If stalk rots were severe, try to determine if there was some underlying problem that caused plant stress, and try to manage that problem. Tillage may or may not be an appropriate step. Other factors, such as hybrid selection, insect and weed control, crop rotation, plant population, fertility, harvest timing, and drainage can be manipulated for stalk rot management. For more information on stalk rot management, see Corn Stalk Rot in Iowa, IPM-50 .
This article originally appeared on pages 185-186 of the IC-478(24) -- November 17, 1997 issue.