Early Blight – Identification, Preventive Measures and Treatment

The main symptom of early blight is round leaf spots with a characteristic target appearance due to the dark concentric rings that develop in most spots. They are about .5 inch in diameter. Spots first appear on older leaves near the base of the plant. The causal fungal pathogen also produces symptoms on stems and fruit. Young seedlings can be killed by stem lesions developing at their base. Sources of the pathogen are infested seed, debris from infected plants left in or on the soil (where it can survive at least 1 year), and spores from other affected plants dispersed typically short distances by wind, water, insects, or animals.

Hosts 

Causes

Symptoms are caused by Alternaria solani, a fungus that overwinters on infected crop debris in soil or on alternative hosts. Purchased seeds or seedlings may also be already contaminated. Lower leaves often get infected when in contact with contaminated soil. Warm temperatures (24-29°C) and high humidity (90%) favor development of the disease. A long wet period (or alternating wet/dry weather) enhances the production of spores, which may be spread via wind, splashing rain or overhead irrigation. Tubers harvested green or in wet conditions are particularly susceptible to an infection. It often strikes after a period of heavy rainfall and is particularly destructive in tropical and subtropical areas.

Prevention

• Use certified pathogen-free seeds or transplants.
• Look for varieties that are resistant to the disease.
• Orient rows in the direction of main winds and avoid shaded areas. Space plants to allow the canopy to dry quickly after rainfall or irrigation.
• Monitor transplants carefully for signs of this disease.
• Keep plants well mulched to minimize soil splashing.
• Water your plants around their base. Avoid wetting foliage.
• Prune off the lowest 3-4 leaf branches once plants are well-established and starting to develop fruits.
• Remove infected leaves during the growing season and remove all infected plant parts at the end of the season.
• After harvest, remove plant debris and burn them (do not compost).

Treatment