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MASTER GARDENERS: What ails my tomatoes?

"I'm not going to grow tomatoes next year. They get blight or some other disease. The leaves get spots, or turn yellow, or the tomatoes have brown/black spots on the bottom. They are not worth the effort!"

We're well into what has been a unique gardening season and the complaints about diseased tomato foliage are heard loud and clear. It seems most gardeners are struggling with tomato blight or septoria leaf spot or blossom end rot.

The first step is knowing which problem the tomatoes have. Let's start with Early Tomato Blight. This disease can attack the plant's leaves, fruit and stems. It appears early to mid-season, is most common in humid weather or with heavy rainfall. The characteristics of early blight are dark, concentric spots (brown to black), ¼ to ½-inch diameter, that form on lower leaves and leathery black fruit rot that starts near fruit stems.

Septoria Leaf Spot is another tomato disease gardeners must battle. It is a fungal disease that appears on the lower leaves after first fruit set. It will gradually move up the plant and badly infected foliage will fall off. It is one of the most destructive diseases of tomato foliage. Like early blight, septoria leaf spot shows up during wet, humid weather that lasts for long periods of time. Poor air circulation is a culprit for both of these diseases.

Prevention is the best control. Rotate crops. The spores of this disease remain in the soil and can infect plants again the next year. Provide plenty of space between plants so the foliage dries more quickly. Water the soil, not the plant, by using soaker hoses. Overhead watering causes the spores to splash onto the plant foliage. We can't keep it from raining, but mulching will help minimize the splashing spores of these two diseases.

Mulch with organic mulch, black or red plastic or landscape fabric to prevent splashing. Trim branches closest to the ground from the stem using sanitized clippers. As the plants grow, watch the lower leaves that start to droop and trim those as well. Stake or cage tomatoes. If caged, be sure to sanitize the cages before reuse. At the end of the season, clean up every bit of tomato foliage and fruit and get rid of it. Do not compost it.

If these organic Integrated pest management techniques fail, you may choose to try a fungicidal spray. These sprays won't cure the infected leaves, but will protect other foliage from becoming infected. Follow the application directions on the fungicide label.

Blossom End Rot is another common problem. It is not a disease but a calcium deficiency in the fruit. Too much nitrogen, irregular watering or even cutting roots when cultivating can cause this imbalance. Water the tomato plants regularly, cultivate carefully and mulch to maintain soil moisture.

When next growing season comes around, it might be hard to resist growing just a couple of tomato plants. Pick a new spot to grow them, mulch, water carefully and pay attention to changes in foliage. Gardeners are optimists. 2019 could be your best tomato year ever!

Tips can be found at the University of Minnesota Extension website at