Early Blight Disease of Potato – A Comprehensive Guide

Early blight is one of the most destructive foliar diseases of potato worldwide. This disease can significantly reduce tuber yield and quality if not properly managed. In this comprehensive guide, we will cover everything you need to know about early blight disease of potato including cause, symptoms, disease cycle, management strategies, and more.

What Causes Early Blight in Potatoes?

Early blight is caused by the fungal pathogen Alternaria solani. This pathogen can infect plants in the family Solanaceae including potato, tomato, eggplant, and some weeds like black nightshade. The early blight fungus overwinters in plant debris, soil, infected tubers, and solanaceous weeds. In spring, spores produced on the debris serve as primary inoculum to initiate infections in potato crops.

Symptoms of Early Blight in Potato

Early blight symptoms first appear on older, lower leaves as small dark brown to black lesions. As lesions enlarge they develop concentric rings giving them a characteristic “target spot” appearance The tissue around spots often yellows Severely infected leaves turn completely brown and die.

Stem lesions are elongated, dark brown, and sunken. Fruit lesions are leathery, black and with concentric ridges mainly near the stem. Infected tubers develop dark, sunken lesions with a raised border and corky texture.

Conditions Favoring Early Blight Development

• Moderate temperatures – 70-80°F
• High relative humidity – 90% or higher
• Long periods of leaf wetness from rain, dew or irrigation
• Older, senescing foliage is more susceptible
• Late in the growing season when plants are stressed

Early Blight Disease Cycle

The early blight disease cycle consists of the following steps

• Primary inoculum overwinters in crop debris and soil
• In spring, spores are produced on debris and serve as primary inoculum
• Spores are spread by wind and rain splash to infect potato foliage
• Lesions develop on leaves 5-7 days after infection
• Numerous cycles of secondary infection occur via spores within a season
• Tubers become infected at harvest due to contact with infested soil
• In storage, tuber infections continue to develop slowly

Integrated Management of Early Blight

An integrated approach combining cultural practices resistant varieties, and fungicides provides the best control of early blight.

Cultural Practices:

• 2-3 year crop rotation with non-hosts
• Eliminate solanaceous weeds and volunteers
• Plant only certified, disease-free seed
• Avoid excess nitrogen and maintain proper fertility
• Plant on raised beds to improve drainage and reduce foliage wetness
• Manage irrigation to minimize prolonged leaf wetness
• Stake plants to improve airflow and foliage drying

Resistant Varieties:

Many potato varieties have partial resistance to early blight. Consult your local extension resources for recommended resistant varieties in your region.

Fungicides:

Foliar fungicides are critical to protect foliage and limit yield loss from early blight. Begin applications after 300 P-Days or when disease first appears. Use FRAC codes to rotate between mode of actions and limit resistance.

Choosing Fungicides for Early Blight Control

Here are some of the most effective fungicide options for early blight management:

• Luna® Tranquility – contains fluopyram (FRAC 7) + pyrimethanil (FRAC 9)
• Luna® Sensation – fluopyram (FRAC 7) + trifloxystrobin (FRAC 11)
• Revus Top – mandipropamid (FRAC 40) + difenoconazole (FRAC 3)
• Zing! – chlorothalonil (FRAC M5) + zoxamide (FRAC 22)
• Bravo® – chlorothalonil (FRAC M5)
• Cabrio® – pyraclostrobin (FRAC 11)

Early blight is a major threat to potato production globally. Integrating resistant varieties, cultural practices, and fungicides provides the best protection against significant yield and quality losses from this disease. Careful monitoring and well-timed fungicide applications are key to limiting damage. Work closely with local extension resources to implement region-specific recommendations for early blight management. With proper control measures, the impacts of early blight on potato crops can be minimized.