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Healthy Tomato Vines

Now is the time to protect your tomato vines from diseases.

Tomatoes and foliar diseases
Protect tomato vines from Septoria leaf spot (lower left) and early blight (lower right) diseases.

Diseases are starting to appear on tomato vines in North Dakota. Now is the time to take action!

The most common diseases are Septoria leaf spot (Septoria) and early blight (Alternaria). Septoria appears as tiny, 1/8-inch-diameter brown spots with dark borders (lower left photo). Early blight lesions may become 1/2 inch or larger, with concentric rings and surrounded by yellow blotches (lower right photo). Here is how to protect your vines:

Water the roots, not the leaves.  Diseases need water on the leaves for infection. Avoid overhead watering. A soaker hose is ideal. Irrigate in the morning so any water that gets on the foliage can dry before nightfall.

Avoid splashing the soil and its infected debris onto the leaves. Avoid working in the garden (and spreading the disease) when vines are wet.

Stake and prune vines.  Staking and pruning will increase air flow and help vines dry out. You may remove up to one-third of leaves at the base to increase air flow and prevent the infection of leaves near the soil. 

Remove severely infected leaves.  Focus on the older and lower leaves, where these diseases will start.

Apply mulch around the vines.  Straw, black plastic or landscape fabric can reduce soil splashing. Lawn clippings can be used if they have not been treated with an herbicide.

Apply protective fungicides.  Chlorothalonil (Daconil, Bravo), mancozeb (Dithane), maneb and copper-based products are often used.  Spray a few days before rains are expected so the chemical is absorbed and can act as a shield. Spray every 7–14 days if needed.

Keep in mind it is unreasonable to expect disease-free vines, but we can slow the spread of diseases and maximize yields until frost.


Written by Tom Kalb, Extension Horticulturist, North Dakota State University.

Sources: Grabowski, M. 2018. Spot check: Look for tomato diseases now.University of Minnesota Extension Yard & Garden News.
University of Nebraska. 2018. Drought Monitor, droughtmonitor.unl.edu/.Home.aspx

Photos were made available under Creative Commons licenses specified by the photographers: Esiul via Pixabay; Missouri Botanical Garden, and Louisiana Plant Pathology Blog.

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