Throughout the year, farmers need to scout corn fields for specific diseases such as gray leaf spot, northern corn blight, tar spot, and common and southern rust. Managing these diseases early is important to keep your crop healthy and prevent widespread yield loss.
Corn disease management requires an integrated approach that leverages best practices as well as high-performance crop protection fungicides and fungicide seed treatments. Below are the five most common corn diseases that you might see year to year. Understanding the causes and symptoms behind each of these diseases is key to protection and prevention.
Gray Leaf Spot
Gray leaf spot is caused by the fungus Cercospora zeae-maydis and occurs nearly every growing season. Symptoms first appear on lower leaves about two to three weeks before tasseling. The leaf lesions are long (up to two inches), narrow, rectangular, and light tan colored. Later, the lesions turn gray. They are usually delimited by leaf veins but can join together and kill entire leaves. Gray leaf spot survives on corn residue and is more prevalent in corn after corn.
Northern Corn Leaf Blight
Northern corn leaf blight, caused by the fungus Exserohilum turcicum, has become an increasingly troublesome disease in the United States because it can cause yield loss when it develops before or during the tasseling and silking phases of corn development. Classic symptoms of NCLB include long, oblong or “cigar-shaped” tan or grayish lesions that form parallel to leaf margins. The lesions produce olive-green or black fungal spores when humidity is high. Infestation occurs during periods of moderate temperatures (64 to 81 °F), wet and humid weather. The fungus requires six to 18 hours of water on the leaf surface to cause infection. The NCLB fungus can survive through the winter on corn residue and can spread to the new crop.
Tar Spot
Tar spot is a fungal disease in corn caused by Phyllachora maydis. When the disease occurs early in the season, it causes black specks to form on the leaves that can limit photosynthesis, resulting in the plant cannibalizing itself for sugar in the stalk, which results in poor standability and lodging. Corn plants are less likely to be able to fill ears prior to black layer and will have an overall loss in kernel weight. The tar spot fungus can overwinter on infested crop debris or be spread from wind-blown debris or splashing rain. Since being discovered in 2015, infections have been noted in Illinois, Indiana, Iowa, Michigan, Ohio and Wisconsin.
Common Rust
Common rust, caused by the fungus Puccinia sorghi, is the most frequently occurring of rust diseases of corn that occurs during exceptionally cool summers and in late-planted fields. The dark, reddish-brown, oval or round pustules of the disease scatter over both the upper and lower surfaces of the corn leaves. Rust development and spread are favorable during periods of cool temperatures ranging from 60 to 74 °F and high relative humidity.
Southern Rust
Southern rust is caused by the fungus Puccinia polysora. Although generally considered a tropical disease, southern rust can occur in important corn production areas of the United States and Canada. Symptoms are similar to common rust, but pustules are smaller and occur almost exclusively on the upper leaf surface. The disease is favored by high humidity and temperatures around 80 °F.
How to Use Fungicides to Protect Plant Health
Maintaining plant health throughout the season is key to preventing yield loss in corn. By reducing stress from lack of nutrients or from other pathogen infection, especially during critical grain fill times, corn has a greater opportunity to maximize yield production.
The first step to managing all five of these fungal diseases in corn starts at planting. Prevent disease from the start by using a fungicide-insecticide in the furrow, such as TEPERA® PLUS HD. It combines a highly systemic fluoxastrobin fungicide, to effectively prevent and control seedling and soil-borne diseases, with bifenthrin, an insecticide that defends against rootworms, wireworms and other insects. With TEPERA PLUS HD, growers can improve stand, uniformity and plant health.
The second step is protecting those plants through the season. Preventative fungicides play an important role in managing disease in corn. Farmers can track environmental conditions that favor disease to ensure they are applying fungicides at the right time. When disease symptoms are seen on the crop, yield damage has likely already occurred.
When choosing a preventative fungicide, look for a product that contains both preventative and curative activity. Preventative application of ZOLERA® FX Fungicide proves to be beneficial due to the product having two active ingredients, fluoxastrobin and tetraconazole, that are delivered at full rates for maximum performance and yield in corn.
The highly systemic strobilurin combined with a highly systemic triazole in ZOLERA FX stops disease development in its tracks by inhibiting spore germination and mycelial growth. The combination delivers more robust disease control with both preventative and curative activity. These additional plant health benefits will ultimately lead to higher yields.
The broad-spectrum activity and dual mode of action also makes ZOLERA FX an ideal partner in a disease management program.
A well-executed fungicide plan will give fields season-long control from fungal diseases. The combination of TEPERA PLUS HD and ZOLERA FX offers growers the greatest opportunity for optimum plant health and yields from root to tip.
Before applying any fungicide, please read and follow all label directions for the best possible results.
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