Northern Corn Leaf Blight (NCLB), alternatively known as Turcicum Leaf Blight (TLB), is a highly destructive foliar disease impacting maize crops, resulting in substantial yield losses globally. The culprit behind NCLB is the fungus Exserohilum turcicum, thriving particularly in warm and humid environments. Maize, or corn, serves as a fundamental food crop for millions, and the emergence of NLB presents a significant challenge to worldwide food security.
Symptoms:
NLB primarily affects the leaves of maize plants. Early symptoms include small, oval-shaped lesions with tan centers and dark borders, resembling cigar burns. As the disease progresses, these lesions coalesce, forming larger necrotic areas that compromise the plant’s ability to photosynthesize. Severe infections can lead to premature leaf death, stalk lodging, and a substantial reduction in grain yield.
Conditions Favouring NLB:
The primary cause of Northern Leaf Blight (NLB) in maize is the fungus Exserohilum turcicum. This pathogen thrives under specific environmental conditions, and its interaction with maize plants leads to the development of the disease. Key contributing factors to the occurrence and severity of NLB include:
1. Fungal Pathogen: Exserohilum turcicum is the causal agent of NLB. The fungus infects maize plants, particularly the leaves, leading to the characteristic symptoms of the disease.
2. Environmental Conditions: NLB is favored by warm temperatures ranging from 77 to 86°F (25-30°C) and high humidity. These conditions create an optimal environment for the fungus to grow and spread.
3. Plant Density and Air Circulation: Dense planting of maize crops and limited air circulation contribute to the spread of NLB. In areas with closely spaced plants, the disease can easily transfer from one plant to another.
4. Plant Stress: Conditions that stress maize plants, such as nutrient deficiency or compacted soils, can make them more susceptible to NLB. Stressed plants may have weakened defense mechanisms, allowing the fungus to establish infections more easily.
5. Previous Infections and Residue: Residue from previous maize crops can harbor the NLB pathogen. When new crops are planted in the same area, the fungus can infect the emerging plants. Crop residue management is crucial in reducing the risk of NLB.
Impact of Northern Leaf Blight on Maize Plants
Northern Leaf Blight (NLB) exerts a profound impact on maize plants, significantly affecting their growth, development, and ultimately, yield. The consequences of NLB infection are multifaceted, encompassing various aspects of plant physiology.
1. Reduced Photosynthesis:
NLB primarily targets maize leaves, causing small oval lesions that expand into necrotic areas. As these lesions accumulate, the plant’s ability to photosynthesize is compromised. The reduction in photosynthetic capacity hampers the plant’s ability to produce energy and vital resources.
2. Premature Leaf Death:
Severe NLB infections can lead to premature leaf death. This accelerates the senescence process, diminishing the overall photosynthetic surface and further limiting the plant’s capacity to produce energy for growth and grain development.
3. Stalk Lodging:
Weakened by the impact of NLB, maize plants become more susceptible to stalk lodging. The structural integrity of the plant is compromised, increasing the risk of stems breaking or bending. This not only affects individual plants but can have cascading effects on neighboring crops.
Quantifying Yield Loss Due to NLB:
The yield loss caused by Northern Leaf Blight varies based on several factors, including the severity of the infection, timing of the disease onset, and the susceptibility of the maize variety. Generally, the impact can range from moderate to severe, with potential yield losses of 10% to 50% or even more in extreme cases.
1. Moderate Infections:
In cases where NLB is moderately present and managed effectively, yield losses may be around 10% to 20%. Timely intervention through fungicides and cultural practices can help mitigate the impact.
2. Severe Infections:
Uncontrolled NLB outbreaks, especially during critical stages of maize development, can lead to yield losses exceeding 30% to 50%. This scenario underscores the urgency of implementing preventive measures to curb the spread of the disease.
Identifying Northern Leaf Blight (NLB) in its Early Stages
Timely identification of Northern Leaf Blight is crucial for effective management and preventing the escalation of the disease. Here are key steps to identify NLB in its early stages:
1. Leaf Lesions:
Look for small, oval-shaped lesions on maize leaves. These lesions typically have tan centers with dark borders, resembling cigar burns. Early detection of these lesions is vital for effective intervention.
2. Lesion Progression:
Monitor the progression of lesions. NLB lesions tend to coalesce, forming larger necrotic areas as the disease advances. Recognizing this pattern helps differentiate NLB from other leaf diseases.
3. Leaf Position:
NLB often starts on lower leaves and progresses upward. Regularly inspect lower leaves for the initial signs of infection. Early intervention on lower leaves can help prevent the disease from spreading to upper leaves.
4. Environmental Conditions:
Be aware of environmental factors conducive to NLB, such as warm temperatures (77-86°F or 25-30°C) and high humidity. Regular monitoring during favorable conditions increases the likelihood of early detection.
Preventive Methods for Northern Leaf Blight:
Effective prevention involves a combination of cultural practices, resistant varieties, and, when necessary, fungicides. Here are detailed preventive methods:
1. Crop Rotation:
Implement a crop rotation strategy to disrupt the NLB disease cycle. Avoid planting maize in the same field consecutively. This helps break the chain of infection and reduces the pathogen’s survival in the soil.
2. Adequate Spacing:
Maintain proper plant spacing to enhance air circulation. Adequate spacing reduces humidity around the plants, creating an environment less favorable for NLB development.
3. Timely Planting:
Plant maize at the recommended time for your region. Avoid early planting in cool, wet conditions that may favor NLB. Optimal planting times contribute to healthier plant development.
4. Fungicide Strategies Against Northern Leaf Blight (NLB)
When confronting the heightened risk of Northern Leaf Blight (NLB), the judicious application of fungicides emerges as a pivotal defense mechanism. The selection of the right fungicide involves a nuanced consideration of regional nuances, compliance with local regulations, the severity of infection, and the disease’s developmental stage. Here’s a closer look at some powerhouse fungicides renowned for their efficacy against NLB:
a. Azoxystrobin:
A stalwart in the fungicidal arsenal, Azoxystrobin takes center stage as a broad-spectrum defender. Operating by inhibiting fungal respiration, it is a stalwart preventive measure. Early-season applications of Azoxystrobin prove instrumental in fortifying maize plants against NLB assaults.
b. Propiconazole:
Enter the systemic prowess of Propiconazole, a fungicide adept at both preventive and curative applications. Its versatility extends to combating various foliar diseases, including NLB. The strategic timing of Propiconazole applications is paramount, ensuring optimal results in disease management.
c. Mancozeb:
Standing as a stalwart protectant, Mancozeb showcases multi-site activity. This fungicide forms an impervious shield on plant surfaces, impeding the germination of fungal spores. Integrating Mancozeb into a comprehensive disease management strategy proves indispensable in the battle against NLB.
d. Trifloxystrobin + Prothioconazole:
Elevate the defense with this dynamic duo – Trifloxystrobin and Prothioconazole. Delivering a harmonious blend of preventive and curative prowess, this combination fungicide presents a broad spectrum of disease control. Its systemic protection acts as a fortress against NLB, ensuring a resilient maize crop.
e. Chlorothalonil:
Unveil the protective shield of Chlorothalonil, a non-systemic fungicide with unwavering efficacy against NLB. Acting as a formidable barrier on plant surfaces, Chlorothalonil thwarts the development and spread of fungal infections. In the battle against NLB, its protective action stands as a cornerstone.
5. Monitor and Scout Fields:
Regularly monitor maize fields for early signs of NLB. Conduct scouting to identify lesions and assess their severity. Early detection allows for timely and targeted interventions.
6. Remove Crop Residue:
Manage and remove crop residue from previous maize crops. Residue can harbor NLB spores, serving as a potential source of infection for new plantings.
Conclusion:
In India, Northern Leaf Blight (NLB) poses a threat to maize crops, affecting growth and yield. The warm and humid climate provides an ideal environment for the NLB-causing fungus. The consequences include reduced photosynthesis, premature leaf death, and stalk lodging, leading to economic losses. Preventive measures, such as choosing resistant varieties, crop rotation, proper spacing, timely planting, and strategic fungicide use, are crucial. Crop residue management is vital to reduce the risk of NLB spores persisting in the soil. Adopting an integrated approach is key to safeguarding maize production and ensuring food security in India.
Note: The conditions mentioned in this article may vary based on specific geographical areas. It is crucial to understand that the use of preventive methods and fungicides may need to be adapted according to local conditions and crop management practices. Farmers are advised to consult with authorized agronomists or local agricultural extension services for tailored guidance and assistance. This article aims to raise awareness about Northern Leaf Blight and its potential impact, serving as a general guide. For precise and region-specific recommendations, seeking professional advice is recommended.
Reference:
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(3) THE NORTHERN MAIZE LEAF BLIGHT DISEASE IN TANZANIA: REASONS AND …. https://esciencepress.net/journals/index.php/JPBG/article/view/2119.
(4) References. https://www.techscience.com/phyton/v91n10/48004/html.
(5) Evaluation of Maize Variety for Northern Leaf Blight …. http://pubs.sciepub.com/wjar/2/5/6/index.html.
