Part 2, Section 2: Corn Pest Management
Corn Pest Management
Disease management should start with planting resistant hybrids, maintaining good soil fertility, practicing crop rotation, and monitoring fields for disease. In order to choose the correct resistant hybrids, knowing what diseases have been present is necessary. Therefore, growers should monitor the occurrence of disease and positively identify the diseases. The best method to monitor disease pressure is through periodically scouting fields from planting through harvest. This way you can note the diseases present and disease pressure to better select hybrids the following year. Collect specimens of diseased materials that exhibit symptoms and send them to your local extension office or the Plant Pathology Disease Clinic for identification.
Although the use of foliar fungicides on corn has increased in Pennsylvania, results on yield impact have been mixed. The two most commonly applied foliar fungicide families, the triazoles and strobilurins, are both very effective in controlling diseases and have been marketed as increasing yield. Both the triazole and strobilurin families of fungicides use very site-specific modes of action and multiple fungal pathogens have developed resistance to one or, in some cases, both fungicide families. The continued use of these chemicals without adequate disease pressure or as prophylactic treatments will further increase the likelihood of resistance occurring. Once pathogens become resistant, there will be few choices chemicals to control them if the diseases become an economic threat.
Foliar Fungicide Considerations
Foliar fungicides can be a great tool for protecting a corn crop under adverse conditions and high disease pressure. Research has found that during certain application periods—namely, late vegetative through tasseling (V8–VT)—fungicides should not be applied with a non-ionic surfactant (NIS) adjuvant. NIS is a typical adjuvant used to facilitate the wetting and uniform spreading of pesticides across the leaf surface, as well as to increase plant uptake of the chemical. The use of NIS during the V8–VT stage of corn growth has increased the likelihood of “Hollow Husk,” or arrested ear development. Arrested ear development is a condition where the corn cob is shortened, there are fewer kernels per cob, and a dried, stunted cob tip results. In some cases, silk does not emerge from arrested ears, so the husk covers a shortened, bare cob. Often the plants affected will display a red or purple-red coloration that starts in the leaves, and eventually the stalk may also appear red or purple. This is due to an accumulation of sugars that were produced to fill developing kernels. This color change is an indication of poor kernel set, not just arrested ear syndrome.