Tomato problems abundant in late summer


By Robin Young

PREVIEW Columnist

Tomato problems are abundant in late summer.

Early blight (alternaria solani), a fungal disease, causes brown leafspots with a distinct target-like pattern. As the disease progresses, leaves yellow and drop, making sun-exposed fruit susceptible to sunscald. Early blight develops first on the lower leaves and moves upward in the plant. Damp weather, close spacing and overhead irrigation promote disease development. Early blight can be minimized by avoiding overhead irrigation that splashes fungal spores onto leaves.

Tomato spotted wilt virus and impatiens necrotic spot virus are two diseases that cause similar symptoms. Affected plants may appear wilted, but tissue remains stiff. Brown leaf spots and stem cankers develop. Some describe the appearance of affected tomato plants as “dirty” or “dusty.” Fruit may be distorted and have distinctive yellow rings or spots.

There is no chemical control for the disease. Affected plants must be removed and destroyed to avoid spreading the virus. Western flower thrips transmit the fungus from infected plants to healthy ones as they feed. Spinosad is recommended for thrips control.

Green or yellow shoulders (the tissue nearest the fruit/stem attachment) appear on ripening fruit due to high temperatures and/or sun exposure. The problem cannot be reversed, but shading plants to decrease fruit sun exposure reduces the incidence on newly developing fruits. Floating row cover fabric can serve this purpose is foliage cover is insufficient.