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Fungus Common to Corn

Fungus Common to Corn

by Laura Cruz

Combat Corn Fungus by Staying Alert

Farmers, by their very nature, are at the mercy of the weather. Sun, wind, frost, and especially rainfall, all play crucial roles in determining the success or failure of a season’s crop. In Colorado, where our farming seasons are typically marked by arid conditions and plentiful sunshine, a heavy rainfall can seem like a blessing.

But what happens when the rain doesn’t stop, and springtime becomes more soggy than sunny? This year, Colorado farmers are grappling with precisely this scenario, an unusually rainy spring.

Dealing with a wetter than usual planting and growing season can pose unexpected challenges, especially for those growing crops like corn. One of the significant issues is an increased potential for various crop diseases, many of which thrive in damp conditions. 

However, fear not, as these challenges can be met and overcome with the right knowledge and strategies.

In this post, we’ll explore some of the diseases that become more prevalent during rainy springs, focusing on corn – a staple crop for many Colorado farms. We’ll delve into the symptoms of these diseases, methods for their prevention, and treatments. Armed with this knowledge, we can turn a potentially soggy problem into a manageable situation, ensuring our crops remain healthy and productive, come rain or shine. So, grab your raincoat, and let’s dive in.

Corn Fungus Types

 Northern Corn Leaf Blight (NCLB): This disease is caused by the fungus Exserohilum turcicum. Symptoms include long, elliptical, grey-green or tan lesions on the leaves. The lesions may eventually turn tan or brown. To manage NCLB, consider planting resistant hybrids, rotate crops, and if necessary, apply fungicides when the disease is first observed and conditions are favorable for disease development.
Gray Leaf Spot (GLS): GLS is caused by the fungus Cercospora zeae-maydis. It’s characterized by small, rectangular, grayish spots on the leaves. Like NCLB, management strategies include planting resistant hybrids, crop rotation, and fungicide application as necessary.
Southern Corn Leaf Blight (SCLB): This disease is caused by the fungus Bipolaris maydis and causes tan, rectangular lesions on the leaves. Management strategies are similar to NCLB and GLS.
Anthracnose Leaf Blight: Caused by the fungus Colletotrichum graminicola, this disease is characterized by oval or spindle-shaped lesions with a tan center and reddish-brown border. Later in the season, it can lead to anthracnose stalk rot, which can cause lodging. In addition to resistant hybrids, crop rotation, and fungicides, proper residue management can help reduce the incidence of this disease.
Fusarium: This disease is caused by the fungus Fusarium verticillioides (formerly known as Fusarium moniliforme). Fusarium ear rot is characterized by a white to pink or salmon-colored mold that often begins at the tip of the ear but can be scattered across the ear. The fungus produces a mycotoxin called fumonisin, which can be harmful to livestock if consumed in large quantities. The disease is often associated with damage caused by insects, particularly ear-feeding insects that create wounds for infection. Management strategies include controlling ear-feeding insects, planting resistant hybrids, timely harvest to avoid further fungal invasion, and drying and storing corn properly to reduce further mold growth.
Corn Smut: This is a disease caused by the fungus Ustilago maydis that forms large, irregular galls on all above-ground parts of the corn plant but especially on the ears. Galls initially are greenish-white, later turn dull gray to black. There are no effective chemical treatments for smut. The best management practices are to plant resistant varieties, practice crop rotation, and bury or remove infected plant parts.
Common Rust and Southern Rust: Both these diseases are characterized by the appearance of pustules on the corn leaves, but the pustules of common rust (Puccinia sorghi) are dark reddish-brown, while those of southern rust (Puccinia polysora) are orange to light brown. Fungicide applications can be effective for controlling rust diseases.
Stewart’s Wilt: This disease is caused by the bacterium Pantoea stewartii and is transmitted by the corn flea beetle. Symptoms start as long, wavy, water-soaked streaks on the leaves that eventually turn necrotic. In severe cases, entire leaves may wilt and die. Cold winters tend to kill flea beetles, thus reducing the risk of Stewart’s wilt. But, in mild winters, the disease can be more severe. Using resistant corn hybrids, managing corn debris and controlling corn flea beetle populations are key in managing Stewart’s wilt.
Goss’s Wilt: Caused by the bacterium Clavibacter michiganensis subsp. nebraskensis, Goss’s wilt is characterized by long, gray-green to black, water-soaked streaks on the leaves. Freckles may appear within the lesions, and a shiny, sticky exudate may be observed. This disease can be managed by planting resistant hybrids, rotating crops, managing corn residue, and controlling weeds.
Tar Spot: This fungal disease is caused by Phyllachora maydis. It produces black, raised, tar-like spots on the upper surface of the corn leaves. Although it’s been relatively minor in the U.S., it has caused significant yield losses in parts of Central and South America. Tar spot is a newer disease in the U.S., first identified in 2015 in Indiana and Illinois. Planting resistant hybrids when available, crop rotation, and fungicide applications can help manage this disease.
Diplodia Ear Rot: Diplodia ear rot is caused by the fungi Stenocarpella maydis and S. macrospora (previously known as Diplodia maydis and D. macrospora). It’s characterized by a white or gray mold that usually starts at the base of the ear. Infected kernels may have a brown discoloration and may appear shrunken. Small, black fungal structures may be visible on the husks or kernels. This disease is often more severe in no-till or minimal tillage systems. Management strategies include crop rotation, residue management, planting resistant hybrids, and timely harvest to avoid ear molds.
Gibberella Ear Rot: Caused by the fungus Gibberella zeae (also known as Fusarium graminearum), this disease is characterized by a reddish or pink mold that usually starts at the ear tip. Gibberella ear rot is often associated with wet and cool conditions shortly after silking. The fungus produces several mycotoxins, including deoxynivalenol (also known as vomitoxin) and zearalenone, which can be harmful to humans and livestock. Control methods for Gibberella ear rot are similar to those for Fusarium ear rot: controlling insects, planting resistant hybrids, timely harvest, and proper grain drying and storage. In addition, crop rotation with non-host crops can help reduce the disease pressure.

 

 

Staying on top of fungus pressure

  • Regular Scouting: This involves walking through the fields on a regular basis (at least once a week, but more frequently during periods of rapid growth or high disease pressure). Look for signs of pests or diseases such as unusual leaf color, holes in the leaves, or wilted plants. Also, check for signs of nutrient deficiency like yellowing leaves (nitrogen deficiency), purple leaves (phosphorus deficiency), or interveinal chlorosis (magnesium or zinc deficiency).
  • Tissue Sampling: For a more detailed analysis, you can take plant tissue samples and send them to a lab for nutrient analysis. This can help you identify if your plants are suffering from any nutrient deficiencies so that you can adjust your fertilization strategy accordingly.
  • Root Checks: Dig up a few plants in different areas of the field to inspect the roots. Healthy corn roots should be creamy white and robust. If they’re discolored, slimy, or have a foul smell, it could indicate a problem like root rot.
  • Pest Trapping: Use pheromone traps or sticky traps to monitor for insect pests. This can give you an idea of which pests are present in your fields and in what numbers.
  • Disease Forecasting Models: Use disease forecasting models, if available for your region. These models use weather data to predict disease risks, helping you decide when fungicide applications may be necessary.
  • Check Ears: As the season progresses, you’ll want to inspect the developing ears of corn. Look for any abnormalities, such as incomplete kernel development or signs of pests like corn earworm.

How to Treat Fungus

Fungal diseases in hybrid corn can pose significant challenges to crop health and yield. However, with a combination of cultural practices, chemical control measures, and appropriate hybrid selection, these diseases can be effectively managed.

  1. Cultural Practices: Good farming practices are the first line of defense against fungal diseases. This includes crop rotation, which helps break the life cycle of many soil-borne pathogens, and proper residue management, which can help reduce the amount of inoculum available to infect the next crop. Good field sanitation, including removal of infected plants and debris, is also essential. Enhancing soil health and ensuring proper field drainage can also help make plants less susceptible to disease.

  2. Resistant Hybrids: Where available, planting disease-resistant hybrid corn can be an effective way to manage fungal diseases. These hybrids have been bred to have natural defenses against specific diseases. While not completely immune, they are less likely to be severely affected by these diseases.

  3. Chemical Control: Fungicides can be a valuable tool for controlling fungal diseases in corn. They are most effective when used as part of an integrated disease management program, along with cultural practices and resistant hybrids. It’s important to apply them at the right time, typically when disease pressure is high, and to rotate fungicides with different modes of action to prevent the development of fungicide resistance.

  4. Regular Scouting: Regular field scouting can help detect diseases early, before they have caused significant damage. Identifying the specific disease causing problems in your field is crucial for choosing the best control measures.

  5. Consulting Experts: Working with local agronomists or extension services can provide valuable advice tailored to your specific conditions. They can help identify diseases, recommend suitable resistant hybrids, and advise on the best fungicides for your situation.

Let’s Sum it Up

Farming in a season of higher-than-average rainfall presents a unique set of challenges, particularly with increased risk of disease pressures. However, armed with a solid understanding of the types of fungal and bacterial diseases that can affect corn – such as Northern Corn Leaf Blight, Gray Leaf Spot, Southern Corn Leaf Blight, Anthracnose Leaf Blight, Fusarium and Gibberella Ear Rot, Corn Smut, Common and Southern Rust, Stewart’s Wilt, Goss’s Wilt, Tar Spot, and Diplodia – farmers can better prepare for and mitigate these risks.

Key strategies for managing these diseases include selecting disease-resistant hybrids, improving soil drainage, implementing nutrient management, considering the use of fungicides, and practicing regular and thorough crop scouting. In particular, understanding the symptoms of these diseases, their conditions for development, and how they spread can greatly assist in early detection and treatment.

Yet, as every farm is unique, it’s crucial to consult with local agronomists or extension services for the best advice tailored to specific circumstances. With knowledge, preparation, and the right strategies, farmers can successfully navigate rainy seasons, protect their crops, and ensure a productive harvest.

Remember, the challenges we face in agriculture are not insurmountable. With every rainy day, there are lessons to learn and opportunities to improve. So, let’s put on our rain boots, step out into our fields, and get to work!

by Laura Cruz