The most rainfall was just over a third of an inch. Data from the Ohio Agricultural Research and Development Station in Western Branch, near South Charleston, Ohio, showed 1.66 inches of rainfall in June compared to an average of 4.2 inches.
Additionally, there were seven days with temperatures above 90 degrees Fahrenheit and eight days with temperatures between 85 and 89 degrees Fahrenheit. The lack of rain combined with the heat has caused plants to dry out quickly, and several days of heavy winds at the end of the month have also dried out the soil.
We also had perfect weather for some tomato diseases to begin to develop. The drop in nighttime temperatures and heavy dew over the last few days of the month were perfect for tomato diseases to develop.
Bacterial spot is a disease that is most likely to occur when humidity is high and temperatures are between 64 and 75 degrees Fahrenheit. It occurred after a cold front dropped the temperatures. Bacterial spot occurs when leaves are wet, humidity is high and temperatures are between 75 and 86 degrees Fahrenheit. We had that disease too.
Don't be surprised if you see both diseases on tomato leaves. The disease usually starts on the lower leaves, and the spores are dispersed by rain or overhead irrigation. Wet leaves overnight are ideal for the spores to germinate and work their way into the leaves.
When these diseases become noticeable, lesions are seen on the leaves, stems, fruits and all parts of the plant. Spots or blotches grow larger and merge, causing the leaves to turn yellow and fall off.
Cleaning is important because the fungus overwinters on leaves and plant debris. Mulching also helps prevent spores from spreading to your plants. Allow good air circulation when planting, and cut off dead leaves and dispose of them promptly.
There are fungicide sprays available that will treat these diseases, but they must be applied before symptoms appear. Leaves may be infected before symptoms appear, so starting spraying early will help prevent infection.
If I have this problem every year, I could also plant disease resistant tomato varieties. The problem is, those varieties are not the ones I would like. For example, I plant Amish Paste, San Marzano and Roma for sauces, which are prone to disease.
Two other diseases that are common at this time of year are early blight and Septoria leaf spot, both of which tend to start at the bottom of the plant and spread upwards.
If you see any disease symptoms on your tomatoes or other vegetables, contact your local agricultural extension service for a check-up before applying any pesticides. Know what you're dealing with before you take action.
Pamela Corle-Bennett is state Master Gardener volunteer coordinator and horticulture educator for Ohio State University Extension. She can be reached at bennett.27@osu.edu.
