Early Blight

Leaf symptoms begin as small dark spots, usually on the older, lower leaves, that enlarge into brown lesions with characteristic concentric rings surrounded by a yellow halo, giving a target-spot appearance. Heavily infected leaves yellow and die, and the disease can move up the plant. On tomato fruit and potato tubers, the fungus causes dark, sunken, leathery lesions, and stem infections can also occur.

Alternaria solani survives between crops on infected residue, in soil, on volunteer plants, and on seed or tubers. Spores (conidia) produced on this residue and on lesions are dispersed by wind and rain splash to infect leaves, and repeating cycles build the disease through the season. Warm temperatures with alternating leaf wetness and drying, along with plant stress, strongly favour infection and sporulation.

• Infected residue, volunteers, soil, and seed or tubers carry the fungus over
• Wind- and rain-dispersed conidia infect leaves, stems, fruit, and tubers
• Repeating cycles intensify the disease over the season
• Ageing and stressed plants are especially susceptible

Potato and tomato are the main hosts, with eggplant and other solanaceous plants also affected. Warm weather, dews and light rains that wet foliage followed by drying, and factors that stress or age the crop, such as poor nutrition, drought, or heavy fruit load, all increase susceptibility and severity.

• Warm temperatures with alternating leaf wetness and drying
• Plant stress from poor nutrition, drought, or heavy crop load
• Infected residue and volunteer solanaceous plants nearby
• Susceptible varieties and older, senescing foliage

Because early blight is favoured by stress and ageing tissue, keeping plants vigorous and well nourished is a key part of management, alongside sanitation, rotation, and resistant varieties. An integrated approach reduces both inoculum and susceptibility.

• Grow varieties with better early-blight tolerance where available
• Maintain vigorous, well-nourished plants to reduce susceptibility
• Use rotation and residue management to lower carry-over inoculum
• Remove volunteers and cull tubers or fruit that harbour the fungus
• Avoid practices that keep foliage wet for long periods where feasible