Growers should always check with their certifying agency prior to using any seed treatment. Chlorine seed treatment is not an acceptable treatment. Hot water seed treatment at 122☏ for 25 minutes is recommended to control early blight on tomato seed. Fungicidal seed treatments are not an option for organic growers however, there are some seed treatments-such as hot water sanitation or National Organic Program (NOP)-compliant protectants-that can be used by organic farmers to eradicate some pathogens from seed.
Further information on organic tomato seed selection can be found in the related eOrganic article Sourcing Certified Organic Seed and the National Organic Program Regulations. The planting of pathogen-free organically produced tomato seed is an important first step in managing early blight disease. Figure credit: Thomas A Zitter, Cornell University Management Seed selection and treatments Figure credit: Fulya Baysal-Gurel, The Ohio State Universityįigure 2. If this arises consecutively on many seedlings, it may indicate contamination of tomato seeds or soil used for planting.įigure 1. Lesions at the base of emerging seedlings can cause collar rot. Stems and petioles affected by early blight have elliptical concentric lesions, which severely weaken the plant (Fig. Fruit on defoliated plants are also subject to sunscald. Infected fruit often drops, and losses of immature fruit may occur. Lesions can become quite large, involve the whole fruit, and have characteristic concentric rings. Fruit can become infected either in the green or ripe stage through the stem attachment. When conditions are favorable for disease development, lesions can become numerous and plants defoliate, reducing both fruit quantity and quality. As the lesions enlarge, they often develop concentric rings giving them a bull's-eye or target-spot appearance (Fig. The tissue surrounding the primary lesions may become bright yellow, and when lesions are numerous, entire leaves may become chlorotic. SymptomsĮarly blight first appears as small brown-to-black lesions on older foliage. Early blight can develop quickly mid- to late season and is more severe when plants are stressed by poor nutrition, drought, other diseases, or pests. Once the primary infections have occurred, they become the most important source of new spore production and are responsible for rapid disease spread. The fungal spores can be spread by wind and rain, irrigation, insects, workers, and on tools and equipment. The disease is favored by warm temperatures and extended periods of leaf wetness from frequent rain, overhead irrigation, or dew. It causes direct losses by the infection of fruits and indirect losses through leaf lesions, which reduce plant vigor. Early blight is common on tomatoes and potatoes, and it occasionally infects eggplants and peppers. These fungi can also be carried on tomato seed. tomatophila, which survive between crops on infected crop residues and on solanaceous host weeds. Sally Miller, Department of Plant Pathology, Ohio State University IntroductionĮarly blight is caused by Alternaria solani and A. Fulya Baysal-Gurel, Department of Plant Pathology, Ohio State University
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