Early blight is one of the most widespread and destructive fungal diseases affecting potato crops Caused by the fungus Alternaria solani, early blight thrives in warm, humid conditions and can completely defoliate potato plants, leading to significant yield losses Read on to learn how to identify, treat, and prevent early blight in your potato crop.
What is Early Blight?
Early blight is caused by the fungus Alternaria solani and can infect potatoes as well as tomatoes, eggplants, and some weeds. The disease first appears as small dark lesions on older leaves near the ground. These spots enlarge into round or irregular brown lesions with concentric rings giving them a “target-like” appearance.
Severely infected leaves turn completely brown and die. The lesions may spread to the stems where they form sunken brown spots with rings. Tubers can also become infected through wounds, causing brown, slightly sunken areas on the potato surface.
Early blight thrives in warm, humid conditions between 70-80°F. The fungus overwinters in crop debris and soil and is spread by splashing water, wind and insects. Lower leaves become infected first through contact with contaminated soil.
Early Blight Disease Cycle
The early blight pathogen survives between growing seasons as spores (fungal propagules) in crop debris and soil. In spring, the spores are splashed onto lower foliage where they germinate and penetrate leaf tissue, producing more spores. These spores are then dispersed by wind and rain to infect more plants.
Disease development accelerates rapidly in warm, wet conditions. Early blight continues spreading upwards through the plant canopy over the course of the growing season. Tubers become infected through wounds or eyes. The fungus produces survival structures in fallen leaves and stems to overwinter.
How to Identify Early Blight
Here are the key signs to look for when scouting for early blight:
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Small dark brown lesions on older lower leaves
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Spots enlarge to 1⁄2 inch diameter brown circles, often with target-like rings
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Tissue around spots turns yellow; leaves brown and die
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Stem lesions are brown, oval, sunken with dark concentric rings
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Potato tubers have leathery brown spots with slight indentations
Compare to late blight, where lesions are pale green to brown, appear on all plant parts, and tuber rot is firm and granular. Septoria leaf spot also causes similar foliage symptoms but lacks the target-like rings of early blight.
Early Blight Damage
Early blight thrives in hot weather and can spread rapidly. Consequences of early blight infection include:
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Premature leaf drop and vine defoliation
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Reduced tuber size and number
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Sunscalded tubers due to lack of foliage cover
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Lower potato quality and yields
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Tuber infections which reduce storability
Complete defoliation can occur in susceptible varieties if early blight is left uncontrolled. Yield losses average 5-10% but can reach 60% or more in severe outbreaks.
How to Prevent Early Blight
An integrated strategy is key to preventing early blight infection and limiting crop damage:
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Plant resistant varieties like ‘Elba’, ‘Pike’, or ‘Rosa’
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Practice a 2-3 year crop rotation with non-solanaceous plants
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Eliminate cull piles and volunteer potatoes
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Maintain proper fertility and avoid excess nitrogen
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Give plants plenty of space for airflow
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Use drip irrigation and avoid wetting foliage
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Hill soil around stems to prevent soil splash
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Control solanaceous weeds like nightshades
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Scout regularly and remove infected plants promptly
Early Blight Treatment and Control
If early blight is detected, prompt action is needed to protect yields. Recommended management options include:
Fungicides
Apply protective fungicides like chlorothalonil, mancozeb, or copper weekly starting when plants are 6 inches high. Rotate fungicide classes to avoid resistance.
Cultural Practices
Promote airflow by hilling and avoid working in wet plants. Remove and destroy heavily infected plants.
Biologicals
Some biofungicides with Bacillus subtilis or Streptomyces lydicus can suppress early blight.
Organic Options
Apply certified organic copper fungicides or biofungicides. Boost plant health with compost tea.
Resistant Varieties
Choose less susceptible potato varieties to limit disease severity.
Crop Rotation
Rotate out of potatoes for at least 2 years to disrupt disease life cycle.
An integrated strategy combining preventive practices and targeted fungicides generally provides the best early blight control. Start applications at the first signs of disease and repeat as needed up to the final fungicide application window before harvest.
Early Blight of Potato: Key Takeaways
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Early blight is caused by the fungus Alternaria solani and thrives in warm, humid conditions.
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Symptoms include brown leaf spots with concentric rings and sunken stem lesions.
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The disease spreads from lower leaves upwards and can also infect tubers.
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Preventive measures include rotation, sanitation, resistant varieties, and avoiding moist foliage.
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Blighted plants should be promptly removed and destroyed.
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Fungicides applied on a 7-10 day schedule can protect against infections.
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An integrated program is most effective for managing early blight.
With vigilance and a multifaceted management plan, the impacts of early blight on potato yields can be minimized. Careful monitoring and timely action at the first disease signs are critical to staying ahead of epidemics. By combining cultural practices, resistant varieties, and targeted fungicide applications, productive, high-quality potato harvests can still be achieved in spite of early blight pressure.
Biology Early blight starts at the bottom of the plant.
- Two species that are very similar can cause early blight: Alternaria tomatophila and Alternaria solani.
- It is possible for both pathogens to infect peppers, tomatoes, potatoes, and weeds in the Solanaceae family, such as black nightshade (Solanum ptycanthum) and hairy nightshade (Solanum physalifolium).
- Disease grows in temperatures between 59 and 80 F; 82 to 86 F is the best temperature range for it.
- It is most likely for the pathogen to spread when it is wet or when there is a lot of dew or when the relative humidity is 90% or higher.
- In Minnesota, the early blight pathogens spend the winter in both infected plant debris and soil. The pathogen can also live on tomato seeds or be brought in on tomato transplants.
- Lower leaves get sick when they touch contaminated soil, either directly or when raindrops splash soil on the leaves. Spores, which are reproductive structures, can grow between 247 and 90 degrees Fahrenheit and need free water or a relative humidity of 90 percent or higher. Plants get spores, which in just five days make leaf spots as small as 1/8 inch across.
- Spores can be spread across a field by wind, people, or tools, so there are many chances for reinfection during the growing season.
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.
It doesn’t mean that there won’t be any early blight; it just means that resistant varieties can handle the pathogens better, 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.
- Use fabric, straw, plastic mulch, or dried leaves as mulch to cover the soil under the plants.
- You can water each plant carefully by hand, with drip irrigation, a soaker hose, or a soaker hose.
- Stake or trellis plants to let more air flow through, get rid of weeds, and make sure plants are far enough apart.
- Cutting off the bottom leaves can also stop early blight spores from splashing onto the leaves from the ground.
- After two years, you can plant peppers or tomatoes in the same spot.
Blight: 5 Ways to Control Potato Blight (Late Blight)
What is early blight of potatoes?
The terms “early” and “late” refer to the relative time of their appearance in the field, although both diseases can occur at the same time. Early blight of potato is caused by the fungus, Alternaria solani, which can cause disease in potato, tomato, other members of the potato family, and some mustards.
What are some of the negative effects of potatoes?
I would say that the potato itself does not have a negative side, it is another food option that we have and that has been part of our food and tradition for a long time. The problem is the way we use and prepare the potato. When we remove the husk, we already lose a good part of the nutrients and fiber. When we fry, we add a huge volume of fat and substances that are not good for our health. When we make a puree loaded with unhealthy ingredients, we lose the essential characteristic of the potato.
Why do potatoes get blight?
In all potato production areas, weather conditions are conducive to the development of early blight disease, and epidemics can occur at any phase of potato growth and is more severe during the late phase of the growth.
What are the most common potato blights?
The most common potato blights are named for the part of the season when they’re common– early blight and late blight. Blight control in potatoes is difficult but armed with some knowledge you can break the disease cycle.
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