Try This Technique: Preventive Pruning for Tomato Early Blight

Reader Contribution by Barbara Pleasant
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Several seasons back, Jeff McCormack, Ph.D., founder of Garden Medicinals and Culinaries and Southern Exposure Seed Exchange, shared a tomato pruning method with me that delays the onset of early blight, and reduces the number of leaves lost in the course of the season.

Extension publications often suggest pruning tomatoes to prevent disease by improving air and light penetration. Jeff’s method concentrates pruning at the base of the plant by removing leaves that eventually will be lost to early blight anyway. When the lowest leaves are removed just as the first leaf spots appear, you also remove millions of spores. And, because the bases of pruned plants dry quickly, the spread of the disease is slowed because early blight fungi need damp leaves in order to germinate and grow.

What’s Early Blight?

The most common leaf-spot disease of tomato, early blight (Alternaria solani) fungi cause leaf spots to form on tomato leaves. Inside irregularly-shaped dry patches (which often have yellow margins), look for small dark rings. These are the fruiting colonies. The grayish powder inside the dark rings are the spores, which splash or blow onto new leaves to form new spots. When spots become numerous, entire leaves wither to brown.

Commercially-grown tomatoes are often sprayed weekly with fungicides to suppress early blight. Organic growers sometimes use copper fungicides, which are often effective, but frequent use may harm earthworms. A few resistant varieties have been developed, but some failed to perform well in field trials, and others fall short in terms of flavor and texture.

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