GARDENING: This is perfect weather for tomato diseases

Credit: Contributed

Credit: Contributed

Not to beat a dead horse, but we still need rain. At least I do in my garden. I finished weeding my tomatoes yesterday and the soil was dry and dusty, even below a couple of inches.

We got rain last week in a few different events, but not enough to saturate a thoroughly dry soil. We could use an all-day soaking, but I would prefer it to happen next week when I am not on vacation!

The most rain we had at any time was a little over a third of an inch. Looking at the Ohio Agricultural Research and Development Station data for the Western Branch near South Charleston, Ohio, we received 1.66 inches of rain in June when the normal precipitation is 4.2 inches.

We also had seven days over 90 degrees and eight days between 85 and 89 degrees. Add the heat to the lack of rain and plants are drying out quickly. In addition, a few windy days towards the end of the month dried the soil.

We have also had the perfect weather for a few tomato diseases to start showing up. The cooler night temperatures along with a heavy dew a few days towards the end of the month were perfect for tomato diseases to develop.

Bacterial speck is a disease favored by high humidity and temperatures between 64 and 75F. We had that after the cold front dropped temperatures. Bacterial spot develops with wet leaves, high humidity, and temperatures between 75 and 86F. We had that also.

I wouldn’t be surprised if you see both diseases on tomato leaves. They typically start on the lower leaves and spores can be splashed with rain or overhead irrigation. Leaves that stay wet during the night are perfect for the spores to germinate and enter the leaves.

When these diseases are prominent, you will also see lesions on the leaves, stems, fruit, and all parts of the plant. As the spots and specks grow, they coalesce, and the leaves turn yellow and drop.

The fungus overwinters on the leaves and plant debris so clean up is important. Mulching will also help keep spores from splashing onto the plant. Provide good air circulation (at planting) and trim any dead leaves and dispose immediately.

There are fungicide sprays that will work on these diseases, but you must apply them prior to the symptoms showing up. The leaves can be infected a few days before the symptoms show up so starting early with sprays helps to prevent infection.

There are also disease resistant tomato varieties that can be planted if you have this problem year after year. The trouble I have is that they aren’t the varieties I want. For instance, I plant Amish paste, San Marzano, and Roma for sauces, and they are susceptible.

Two other common diseases that you may see at this time are early blight and septoria leaf spot. Both also tend to start at the bottom of the plant and work their way up.

If you are seeing symptoms of disease on tomatoes and other vegetables, contact your local Extension office for verification before spraying pesticides. Know what you are dealing with before acting.

Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at

Credit: Contributed

Credit: Contributed

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