Tomato Plant Diseases Identification


A great deal of pride and satisfaction can be gained from growing a successful tomato harvest. There are many types of bacteria, fungus and viruses that a gardener needs to be aware of to produce a healthy crop. If you know how to identify signs of these various diseases, you may be able to catch and treat problems before they harm your plants or spread throughout your garden. There are many signs you can look for to identify a disease in your tomato plants.

Fungal Leaf Spots

There are two types of fungus that can affect the health of tomato plants and show signs in the leaves. Septoria leaf blight can appear after fruiting on the lower leaves of tomato plants. It is caused by Septoria lycopersici and can be identified by tiny black spots and dark gray margins. Later, the leaves may yellow and fall. Another fungus, Alternaria solani, causes "early blight," which forms large brown or black spots on leaves. It starts on the lower leaves of plants and can quickly spread to upper leaves.


Brown, circular, 1/16-inch specks on tomatoes or plant leaves may be a sign of the tomato bacteria Psedomonas syringae pv. The specks will appear raised and will affect the ability of tomatoes to ripen. Scabby spots on fruits and leaves is a sign of another type of bacteria known as Xanthomonas campestris pv. Vesicatoria. Another type of bacteria known as Corynebacterium michiganese pv. Michiganese, or bacterial cankers, can be identified by slightly raised white blisters on the tomatoes. The lower leaves will also wilt before the spots appear.


Rot in fruit or timber of tomato plants is typically caused by either soil-borne fungus or mold fungus. Rizoctonia solani is a soil-borne fungus that causes soft, brown-colored rot to appear on tomatoes that touch the soil. These fruit also tend to crack open. Timber rot is caused by Sclerotinia sclerotiorum. This fungus is a white mold that can cause root rot and kill plants. It can occur when soil is overly wet for long periods.


Fusarium and Verticillium wilt are two types of wilt diseases that attack tomatoes. Each is caused by either the fungi Fusarium oxysporum f. sp. Lycopersici or Verticillium albo-atrum. Verticillium wilt and Fusarium wilt are impossible to diagnose without a lab test because they look very similar. Both are distinguished by yellowing and drooping leaves on the lower part of tomato plants. Tomato plants often die from these infections.

Mosaic Virus

Tobacco and cucumber mosaic viruses are two types of viral infections that can effect tomatoes. The tobacco mosaic virus can spread through debris, soil or seed. It can be identified by light and green mottled leaf spots. It can also be spread from garden tools or the gardener. Plants suffering from cucumber mosaic will appear fern-like with yellowed leaves because of stunted growth. The leaves tend to grow long and narrow when the plant's growth is stunted.

Keywords: tomato plants, tomato plant diseases, tomato disease identification, growing tomatoes

About this Author

Based in Ann Arbor, Michigan, Robin Coe has reported on a variety of subjects for over 15 years. Coe is the former publisher of the politics and art magazine Flesh from Ashes. She has worked to protect water and air quality. Coe holds a Bachelor of Science in journalism with a double-major in international politics from Bowling Green State University.