Blight spreads by fungal spores that are carried by insects, wind, water and animals from infected plants, and then deposited on soil. The disease requires moisture to progress, so when dew or rain comes in contact with fungal spores in the soil, they reproduce.

What causes early blight?

Early blight can be caused by two different closely related fungi, Alternaria tomatophila and Alternaria solani. Alternaria tomatophila is more virulent on tomato than A. solani, so in regions where A. tomatophila is found, it is the primary cause of early blight on tomato.

Why do tomatoes get blight?

Blight on tomatoes is caused by a fungal infection and like all fungi, they are spread by spores and require damp, warm weather conditions to flourish.