NDSU Extension - Morton County


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July 27, 2020 Common Tomatoe Problems

Kelsey Deckert, Extension Agent/Horticulture


Common Tomato Problems

Many gardeners are starting to harvest produce from their gardens.   As you harvest you may notice different issues with your tomatoes. Three common problems are: Blossom End Rot, Tomato Blight, and Bacterial Spot.

First fruits may have a brownish black spot on the bottoms of the tomatoes, which is the most common symptom of Blossom End Rot. This is pretty typical to see and caused by a calcium deficiency.  Simply pick of these fruits, as future fruits should be fine.  Mulching around the plants will help keeping the moisture consistent.

Tomato Blight can be seen on both the foliage and fruit itself.  Symptoms of the foliage appear as large, irregular brown lesions with concentric rings.  Surrounding tissues of these lesions turn yellow.  Blight is a fungus that comes from the soil and starts on the plant’s lower leaves.  Fungicides are available to help prevent the spread of blight onto other tomato plants, but are not a curative to already infected plants.  Chlorothanil, mancozeb, or copper can be used.

Bacterial Spot causes spots on both the foliage and fruit of the plant which can lead to defoliation, sun-scalded fruit, and yield loss.  These spots are dark and corky usually the size of the diameter of a pencil eraser. Copper fungicides can be used to prevent the spread of Bacterial Spot.

However, a combination of gardening practices is the best way to help prevent and manage Tomato Blight and Bacterial Spot.

Monitor your soil’s fertility.  Early blight is aggressive on pale, hungry vines.  Tomato plants benefit from a light fertilizer after the first fruit set.  Water at the base of the plant mid-morning rather than overhead watering as it can spread it from one plant to another.  Space your plants correctly. Mulching, staking, and pruning your plant will benefit your plants.  Mulching can provide a barrier from the soil and conserve moisture. Staking the plants increases sunlight and air flow.  If your plants do get infected, remove any infected parts of the plant.  Use crop rotation and look for resistant varieties to purchase.

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