We are just beginning the time of year when most disease management takes place. Most of the tactics used to manage diseases in the 1997 crop will occur before planting begins. These tactics include planning for rotation, tillage, and variety selection. The most immediate decision is whether fall tillage is appropriate for managing disease problems.

Most corn and soybean pathogens survive in crop residue so their populations can be reduced by tillage operations. When residue is buried, pathogens must compete with soil microorganisms for food (the residue), which can rapidly decompose. Pathogen survival also is reduced because of direct attack by antagonistic soil microorganisms.

Residue left on the surface lasts longer, and so do the pathogens. Fall tillage is typically more effective in reducing pathogen populations than spring tillage because the residue is buried longer before planting. Pathogen survival usually is shortest if residue is completely buried. However, partial burying by chopping, disking, or chiseling also is beneficial. For seedling diseases, pathogen survival may be reduced, but the major effect of tillage is probably more rapid warming of soil in the spring. In this case, spring tillage can be as effective as fall tillage.

Keep in mind that many, but not all, diseases can be reduced by tillage. In a few cases, tillage can make a disease problem worse. You should check ISU Extension publications for information on the effects of tillage on specific diseases.

Many factors influence tillage decisions, and each grower must select priorities for individual fields. In fields that had serious disease problems in 1996, disease management for 1997 should be a high priority.

Fall tillage reduces the risk of many diseases in any field, but the disease risks must be weighed against the disadvantages of tillage (such as soil erosion). In many fields, diseases can be well managed by other means, particularly selection of disease-resistant varieties and crop rotation. Fields with a history of difficult-to-manage disease problems should be considered for fall tillage.