Submitted by Faye Mahaffey
Brown County OSU Extension Master Gardener Volunteer
Leaf spot diseases of tomatoes enjoy the warm, humid weather that most of us experience in Ohio. Many of these leaf spot diseases can mimic each other in their early stages of development.
If you have access to a computer, I highly recommend visiting the Ohioline website http://ohioline.osu.edu to look at Fact Sheet HYG-1624-10. Authors, Gary Gao, Brad Bergefurd, and Bob Precheur provide readers with a fantastic list of suggested tomato cultivars to use in the home garden. Information on: Climate requirement, Site Requirements, Sunlight Requirements, Fertilization, Disease Resistance, Establishing the Plants, Plant Spacing, Supporting Tomato Plants, Growing Tomatoes in Containers, Watering Tomato Plants, Mulching, Diseases, Insects, Weed Control, Harvest and Storage, and Special Problems with Tomatoes, will help the home gardener increase their harvest.
I have received some phone calls and there are loads of photos on Facebook about spots on tomato leaves, so I am hoping this information will help gardeners determine what may be affecting their tomato plants. Proper diagnosis will help one select the most appropriate management for each disease.
*Early Blight– This is a fungal disease that can infect all above ground parts of the tomato plant. The symptoms usually begin on the leaves and start out as small necrotic (brown) spots that expand rapidly and eventually grow together, usually from the bottom of the plant, up. There is usually a small yellow halo surrounding the necrotic region. These symptoms eventually form a bull’s-eye appearance and cause leaf defoliation. Fruit symptoms include concentric rings of dead tissue, also giving the lesion a bull’s-eye appearance, these spots become large and eventually will cause fruit drop. This disease overwinters on infected plant material in the soil and seed. An OSU Extension Fact Sheet on “Early Blight of Potato and Tomato” can be found at: http://ohioline.osu.edu/hyg-fact/3000/pdf/3101.pdf.
*Late Blight– This is a fungal disease that infects quickly and can infect all above ground parts of the tomato plant. Rapid fungal development is usually enhanced by humidity and rainfall. This disease creates brown, water-soaked, or greasy lesions on stems, leaves, and fruit. Management of this disease is very important. An OSU Extension Fact Sheet on “Late Blight of Potato and Tomato” can be found at: http://ohioline.osu.edu/hyg-fact/3000/pdf/3102.pdf.
*Septoria Leaf Spot– Septoria is a fungal disease of tomatoes that affects the foliage. In some cases, the disease can be so severe that it defoliates the entire plant in a growing season causing little to no fruit production. This disease produces lesions that are usually brown, circular, and small with a yellow halo. Fungal fruiting bodies known as pycnidia can be seen usually in the middle of the mature lesion as tiny, black dots. Septoria starts on the lower leaves and works its way up the plant. Sanitation is key in managing this disease. An OSU Extension Fact Sheet on “Septoria Leaf Spot of Tomato” can be found at: http://ohioline.osu.edu/hyg-fact/3000/pdf/3112.pdf.
By now you know that the Mahaffey household loves their tomatoes. My husband wants me to hang a water-proof saltshaker on the Texas Tomato Cages so he can salt as he grazes in the tomato patch. Not a bad idea, really.
I found a great quote from Lewis Grizzard that says, “It’s difficult to think anything but pleasant thoughts while eating a home-grown tomato.”
Here’s hoping for a long and bountiful tomato season!