Corn Foliage Disease Outbreak in Northern Regions
Managing Northern Corn Leaf Blight (NCLB) in Corn Production
The northern corn leaf blight (NCLB), a common foliar disease of corn in Ohio and the Midwest, is caused by the fungus Exserohilum turcicum. This disease can significantly impact crop yield if not properly managed.
NCLB lesions on susceptible hybrids are cigar-shaped, gray-to-tan colored, and approximately one-to-six inches long. As the disease progresses, these lesions spread to all leafy structures, including husks, and produce dark gray spores. Before lesions are fully developed, they appear as small light-green to grayish spots.
Effective management of NCLB in commercial dent corn production primarily involves the use of resistant hybrids combined with timely fungicide applications. Selecting corn hybrids with genetic resistance or tolerance to NCLB significantly reduces the severity of the disease. Seed guides from reputable companies often rate hybrids for their tolerance to leaf diseases, including NCLB. Using hybrids with average to high tolerance is an important preventive strategy that can reduce reliance on chemical controls.
Applying fungicides at the appropriate growth stages can help suppress NCLB. Target fungicide applications typically from tassel (VT/R1) through the milk (R3) stage of corn development. In some cases, an additional application might be valuable at the dough stage (R4), but this is less common. Fungicide products with mixed modes of action are recommended to improve disease control and reduce the risk of resistance development.
Regular field scouting, especially during reproductive stages, helps monitor disease presence and severity, enabling more informed fungicide application decisions and avoiding unnecessary sprays.
An integrated approach that combines hybrid resistance, judicious fungicide use, and crop management practices like crop rotation can reduce inoculum pressure and disease impact. However, fungicide application timing and environmental conditions remain crucial.
While the search results did not provide detailed specifics on NCLB fungicide products or exact hybrid names, Michigan State University Extension strongly emphasizes the importance of knowing your hybrids' disease ratings and using fungicides strategically at key growth stages to manage foliar diseases such as NCLB.
Two types of resistance are available to protect against these races: partial resistance and race-specific resistance. Partial resistance reduces the rate of disease development, reduces the number and size of lesions, and increases the length of the incubation and latent periods. It is controlled by multiple genes and protects against all known races of the fungus. On the other hand, race-specific resistance is controlled by single Ht genes (Ht1, Ht2, Ht3, and HtN) and protects against specific races of the pathogen.
Under favorable conditions, lesions develop and produce new spores within 7-12 days on susceptible hybrids, causing the disease to spread rapidly. Spores are primarily spread through rain, while wind is responsible for long-distant spore movement.
A one- to two-year rotation away from corn and destruction of old corn residues by tillage can help control NCLB. The fungus causing NCLB overwinters as mycelia, conidia, and chlamydospores on corn residues left on the soil surface.
Planting resistant hybrids is the most effective method for controlling NCLB, specifically hybrids with both partial and race-specific resistance. Several fungicides are available for use on corn for NCLB control, and labels and application directions should be read carefully for each fungicide product. If leaf damage is moderate or delayed until 6 weeks after silking, yield losses are minimal. However, severe NCLB damage can lead to yield losses of up to 50%, especially during wet weather. Fungicide sprays are recommended for fresh market sweet corn, hybrid seed production, and dent corn fields planted with susceptible hybrids, with applications starting when the first lesions appear on the leaf below the ear on 50% of the plants.
Soil management practices, such as crop rotation and destruction of old corn residues, can help control the northern corn leaf blight (NCLB) by reducing inoculum pressure.
Understanding the disease ratings of corn hybrids and utilizing ones with both partial and race-specific resistance is the most effective method for managing NCLB, which is a crucial health-and-wellness aspect in corn production.
