Early blight is one of the most widespread and destructive diseases affecting potato crops worldwide This fungal disease is caused by the pathogen Alternaria solani and can lead to severe defoliation and significant yield losses if left uncontrolled In this article, we will dive deep into early blight disease to understand its symptoms, life cycle, spread, and most importantly, how to effectively manage it.
What Exactly is Early Blight Disease?
Early blight, caused by the fungus Alternaria solani, is a foliar disease that attacks leaves, stems and tubers of potatoes. It is found wherever potatoes are grown but thrives in areas with warm, humid conditions.
The disease first appears as small, dark brown to black lesions on older leaves near the bottom of potato plants. These round or irregular spots enlarge into brown targets or “bull’s eye” shaped lesions about 1/4 to 1/2 inch in diameter, often marked with concentric rings.
As the spots increase in number and size, affected leaves yellow and die off. Entire plants can be rapidly defoliated, appearing scorched and dried up Stem lesions are also possible, with elongated black sunken areas that crack Tubers can become infected through wounds, developing brown, leathery patches of dry rot.
Recognizing the Symptoms
Detecting early blight promptly is crucial for effective management. Here are the telltale signs to look out for when scouting potato fields:
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Small dark brown to black spots on lower older leaves
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Spots enlarge into 1/4 to 1/2 inch brown target-shaped lesions circled with rings
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Dead brown areas around lesions surrounded by yellowing
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Severe defoliation of plants as disease progresses
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Elongated dark sunken lesions on stems
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Dry, brown rotting spots on potato tuber surfaces
The Early Blight Disease Cycle
To control early blight, it’s important to understand how the disease spreads and survives between growing seasons:
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The fungus overwinters as spores in crop debris and soil. It can also survive on infected seed tubers.
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In spring, spores are splashed onto lower leaves or shoots touch contaminated soil, initiating infections.
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7-14 days after infection, lesions develop and produce more spores.
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Wind, rain, insects, machinery spread spores to new plants.
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Lower leaves are infected first, with disease moving up the plants over season.
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Tubers become infected through eyes, cuts or wounds at harvest.
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The cycle repeats as the pathogen survives winter in debris.
Why Early Blight Disease is so Destructive
When early blight takes hold in a susceptible potato variety under favorable weather conditions, the impacts can be devastating:
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Premature defoliation reduces photosynthesis and weakens plants.
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Smaller, fewer tubers are produced lowering yield significantly.
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Sunscalding of exposed tubers degrades quality.
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Infected seed tubers have poor emergence and vigor.
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Tuber infections reduce storability and marketability.
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Entire crops can be destroyed resulting in 100% yield loss.
Managing Early Blight Disease in Potato
While challenging to control, a multifaceted integrated pest management plan can effectively minimize early blight damage:
Cultural Practices:
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Plant resistant varieties – ‘Elba’, ‘Pike’, ‘Rosa’, etc.
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Use certified disease-free seed.
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Follow 2-3 year crop rotations with non-hosts.
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Eliminate cull piles and volunteer potatoes.
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Allow for adequate soil fertility and plant nutrition.
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Avoid excess nitrogen.
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Use drip irrigation and avoid wetting foliage.
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Hill soil around stems to prevent splash dispersal.
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Increase spacing for airflow.
Monitoring:
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Scout fields weekly looking for symptoms.
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Dig up plants to check tubers for infections.
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Keep records to track disease development.
Chemical Control:
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Apply protective fungicides like chlorothalonil, mancozeb, or Qol’s preventively.
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Start applications at first disease signs and reapply every 7-14 days.
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Rotate fungicide classes to avoid resistance.
Organic Options:
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Spray certified organic copper products.
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Apply biological fungicides with Bacillus subtilis.
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Improve plant health with compost teas.
The Key to Beating Early Blight
Early blight can be intimidating with its potential for explosive spread and severe defoliation. However, by scouting diligently, diagnosing early, implementing cultural practices to reduce disease pressure, and utilizing targeted fungicide sprays, even highly susceptible varieties can produce good yields.
The most critical factors are planting resistant varieties when available, practicing crop rotation, maintaining general plant health, and taking action at the first disease signs. Integrating multiple tactics provides the best early blight control and can hold this destructive pathogen at bay.
Now that you understand the early blight disease cycle and impacts, you can craft a robust management plan suited for your potato fields. Pay close attention to weather patterns, scout regularly, and be prepared to respond promptly at the first spots. With proper control measures, early blight does not have to mean devastating losses.
Managing early blight in the home garden Early blight lesions on tomato leaves
Early blight-resistant varieties are readily available. As early blight occurs commonly in Minnesota, gardeners should look into these varieties.
Resistance does not mean you will not see any early blight; rather, resistant varieties can better tolerate the pathogens, and so the damage will be less severe than with non-resistant varieties.
Cornell University keeps track of varieties sold as having disease resistance. You can often find this information in seed catalogs.
- Cover the soil under the plants with mulch, such as fabric, straw, plastic mulch, or dried leaves.
- Water at the base of each plant, using drip irrigation, a soaker hose, or careful hand watering.
- Increase airflow by staking or trellising, removing weeds, and spacing plants adequately apart
- Pruning the bottom leaves can also prevent early blight spores from splashing up from the soil onto leaves.
- Let two years pass before you plant tomatoes or peppers in the same location.
Biology Early blight starts at the bottom of the plant.
- Early blight can be caused by two closely related species: Alternaria tomatophila and Alternaria solani.
- Both pathogens can infect tomatoes, potatoes, peppers, and several weeds in the Solanaceae family including black nightshade (Solanum ptycanthum), and hairy nightshade (Solanum physalifolium).
- Disease develops at moderate to warm (59 to 80 F) temperatures; 82 to 86 F is its optimum temperature range.
- The pathogen is most likely to spread with wet weather or heavy dew, or when relative humidity is 90% or greater.
- The early blight pathogens both overwinter in infected plant debris and soil in Minnesota. The pathogen also survives on tomato seed or may be introduced on tomato transplants.
- Lower leaves become infected when they come into contact with contaminated soil, either through direct contact or when raindrops splash soil onto the leaves.
- Spores (reproductive structures) can germinate between 47° and 90° F and need free water or relative humidity of 90% or greater.
- Spores infect plants and form leaf spots as small as 1/8 inch in diameter in as little as five days.
- Spores can be spread throughout a field by wind, human contact or equipment, resulting in many reinfection opportunities throughout a growing season.
Blight: 5 Ways to Control Potato Blight (Late Blight)
FAQ
How do you treat early blight in potatoes?
- Disease free seed tubers should be used for planting.
- Removal and destruction of infected plant debris should be done because the spores lying in the soil are the primary source of infection.
- Very early spraying with Zineb or captan 0.2% and repeating it for every 15 – 20 days gives effective control.
What are the first signs of potato blight?
How do you treat early blight?
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- Crop rotation: Rotating crops helps break the disease cycle by preventing the build-up of fungal spores in the soil.
- Avoid overhead irrigation: Overhead irrigation can splash fungal spores onto healthy plants, so drip irrigation or soaker hoses are recommended.
- Improve air circulation: Staking plants or pruning branches can improve airflow, which helps keep leaves dry and reduces the risk of fungal growth.
- Crop rotation: Rotating crops helps break the disease cycle by preventing the build-up of fungal spores in the soil.
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- Prune and discard: Remove and discard all affected leaves and stems to prevent the disease from spreading to other plants.
- Burn or bury: Disposing of infected plant material in a way that prevents further spread, such as burning or burying, is crucial.
- Prune and discard: Remove and discard all affected leaves and stems to prevent the disease from spreading to other plants.
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Fungicide Application:
- Synthetic Fungicides: Copper-based fungicides are a common choice, but it’s essential to follow label instructions carefully.
- Organic Fungicides: Options like baking soda spray or garlic infusion can be used as alternatives to synthetic fungicides.
- Timing is key: Fungicides should be applied early in the season, before symptoms appear, or at the first sign of infection.
- Repeat applications: Regular applications may be necessary, especially during wet weather, to maintain control.
- Synthetic Fungicides: Copper-based fungicides are a common choice, but it’s essential to follow label instructions carefully.
What is the best fuNgiCiDe for potato early blight?
LATe bLIghT And eArLy bLIghT – No MatCh foR Revus toP fuNgiCiDe. When the same disease control options aren’t enough for late and early blight, potato growers rely on the superior performance of Revus Top® fungicide.