Part 2, Section 2: Corn Pest Management
Corn Pest Management
DISEASES
Seed and Seedling Diseases
Corn planted into cold, wet soils sometimes is in the ground for 3 to 4 weeks before emergence. Under these conditions, seed and pre-emerged seedlings are quite susceptible to attack by soilborne pathogens. The use of conservation tillage practices, particularly no-till, also results in seed being placed into cooler soils. As growers move to earlier planting dates and increase their use of conservation tillage, interest in fungicide seed treatments on corn has increased. Essentially 100 percent of commercially sold corn seed is treated with a fungicide or mixture of fungicides to aid in the control of disease. Until recently, Captan was the product used on nearly all seed. Two newer products (Apron and Maxim) are now replacing Captan or, in the case of Apron, being used in combination with Captan.
Captan is an excellent, broad-spectrum fungicide that has been used on corn seed for decades. Its primary weakness is that it has limited activity against species of Pythium, a fungus that is almost always present in soils and takes advantage of the slow emergence and seedling growth that occurs with low soil temperatures.
Apron is a narrow-spectrum fungicide with excellent activity against Pythium. Apron plus Captan has been a popular combination in recent years. Apron XL LS is a more active isomer of the original product and can be used at a lower rate.
Maxim is a broad-spectrum fungicide that is very effective against many soil fungi but is not effective against Pythium. Thus, it is always used in combination with Apron. The switch to a Maxim XL/Apron combination has occurred because Maxim XL can be used at a much lower rate than Captan and creates less dust than Captan.
Dynasty (azoxystrobin) is a new seed treatment with the same active ingredient as Abound or Quadris. Dynasty is being marketed as a broad-spectrum systemic fungicide providing protection to against many classes of fungal diseases, including Pythium, Fusarium, and Rhizoctonia. Dynasty will likely be offered with Maxim XL to ensure a good protection package.
Disease Management
Disease control may be enhanced by planting resistant hybrids. It is essential for growers to know what diseases are likely to occur; therefore, growers should monitor the incidence of disease to obtain positive identification. Scout fields in late August or early September and note the diseases present. With this information you can make knowledgeable decisions when selecting hybrids the following year. Collect specimens of leaf materials that exhibit disease symptoms and send them to your local extension office for identification.
Although the use of fungicides on corn has increased in Pennsylvania, results on yield impact have been mixed. It is important to know what disease you are trying to control, and if possible plant resistant varieties. The widespread use of fungicides to control diseases is not a good management practice. With continued use of fungicides, there is an increased chance for resistant fungal strains to develop. Once resistant, if the diseases do become and economic threat there will be few choices to control them.