Disease management is necessary in any crop to protect yield. An integrated approach using several practices is usually recommended. In corn production, the most commonly recommended disease management tactics include hybrid selection, rotation, residue management, and fungicide applications.
In corn-on-corn fields, since rotation is not being practiced, the potential for yield loss due to increased disease is greater. This is because many of the common corn diseases that occur in Iowa are caused by pathogens that survive on infected corn residues. Rotation to nonhost crops of the pathogen allows time for decomposition of infected crop residues, which deprives pathogens of a food source and exposes them to antagonistic endemic soil microbes.
Therefore, rotation helps to naturally eradicate many pathogens from the soil, decreases inoculum levels, and reduces the risk of disease development. Surface residues also modify the soil environment (cooler soil temperatures, higher soil moistures), which can affect disease development.
Can we mitigate disease risks in corn following corn? Yes, but it is going to take a little more thought, care, and attention than we may be used to. Getting into the field to scout for disease outbreaks will be necessary if economically effective management decisions are to be made.
Careful selection of hybrids is possibly the most important factor for managing disease in corn-following-corn situations. Knowledge of diseases that occurred in the previous crop will enable informed decisions to be made. Opt for hybrids with high yield potential, good resistance to leaf and stalk diseases, and good emergence and seedling vigor traits.
Strip tillage or removing residue above the planting row may be worth considering in high risk disease situations. Once again, the history of disease in each field will help in this decision. In situations where disease severity in the previous crop was high, strip tillage should reduce disease risk by burying some residue and removing residue from direct contact with the crop.
In cooler soils, germination, seedling emergence, and seedling development are delayed thus lengthening the period when germinating seedlings are vulnerable to infection by seedling pathogens and insects. Delaying planting until soil temperatures are above 55 °F will reduce the risk of poor stand establishment due to seedling disease. Consider planting your corn-on-corn fields after planting the corn-on-soybean fields.
Seed treatment fungicides are a critical component of an integrated disease management strategy on corn. New active ingredients continue to be developed and adopted by the seed industry. Currently, there are additional options to purchase seed with insecticidal seed treatments as well as fungicidal seed treatments; these may contribute to seedling disease management by protecting the seed and seedling against root feeding by insects, which can be followed by fungal infection.
Over the past decade or so, the use of foliar fungicides in hybrid corn has rarely been economically feasible. However, since foliar disease incidence/severity tends to increase in high residue environments, and corn prices are more favorable, application of a fungicide in corn-following-corn fields may be warranted. The goal of any fungicide application should be to protect the ear leaf and leaves above the ear from leaf diseases during the grain fill period (silking to black layer), because these leaves contribute more than 75 percent of the carbohydrates. Since all fungicides have limited period of activity (14-21 days), timing of fungicide application is critical. Applications are necessary if a few lesions are observed on the leaves below the ear leaf prior to or at silking. Therefore, fields must be scouted regularly to determine if a fungicide application is needed, and the appropriate time for that application. Hybrid susceptibility and imminent weather conditions also should be considered before applying a fungicide.
Alison Robertson is an assistant professor of plant pathology with extension and research responsibilities in field and forage crops. Gary Munkvold is an associate professor of plant pathology and seed science endowed chair in the Iowa State University Seed Science Center with research and teaching responsibilities in seed pathology.
This article originally appeared on pages 4-5 of the IC-498 (1) -- February 12, 2007 issue.