News release: Tomato Diseases

Tim Baker, MU Extension Horticulture Specialist
102 N. Main, Suite 1, Gallatin, MO 64640

Release Date: July 21, 2016
Headline: Tomato Diseases

The most common diseases that infect tomatoes can be divided into three types: fungal, bacterial, and viral.  Diseases caused by fungi are often the easiest to control.  Bacterial diseases are a bit more difficult, and viral diseases are essentially impossible to control, once established in the plant.  There are many kinds of diseases in each of these categories known to infect tomatoes, but I will only give an example or two of the most common diseases in each category, and how they might be treated.

In Missouri, you can always assume that you will see some fungal diseases in your tomatoes.  Our weather here really encourages their development and spread, so you will probably want to take preventive measures to insure their control.  This often means spraying a fungicide.

A typical fungal disease is early blight.  This disease causes spots on older leaves, although it can affect seedlings.  It also can destroy fruit as well.  Fungal leaf-spotting diseases such as early blight can be controlled with fungicides.

Other fungal diseases may not be so easily controlled, once established.  This applies especially to fungal wilt diseases such as fusarium wilt.  This is a soil-borne disease which can remain in the soil for a long time.  Fortunately, for tomatoes, there are varieties which are resistant to fusarium wilt.  The best approach is to choose varieties which have resistance to this disease.  Be aware that there are different races of fusarium wilt, and fusarium wilt resistant tomato varieties are not usually resistant to all three races. ‘Better Boy’, for example, is resistant to race 1, but not races 2 or 3.

Bacterial diseases also can affect tomato.  In some years, we have seen problems all around Missouri with bacterial spot.  This disease can affect both the foliage and fruit.  Sprays containing fixed copper are the most effective control measures for bacterial diseases in tomatoes.

Viral diseases are the worst problem, since once the plant has the disease, there is no control.  These diseases are typically spread by insects, especially aphids.  They may feed upon nearby weeds which harbor the disease, and then transmit it to your tomatoes when they start feeding on them.  If you see a lot of aphids on your tomatoes, it’s best to control them as soon as possible.  Eliminating weeds in your area which might host viral diseases is also a good idea.  Examples of viral diseases which affect tomatoes include cucumber mosaic virus and tobacco mosaic virus.

I should also mention another pest which can sometimes affect tomatoes.  Root knot nematodes are microscopic roundworms that feed on plant roots, forming galls in the area that they feed. This inhibits the uptake of water and nutrients. Fortunately, for tomato growers, there are nematode-resistant varieties that you may choose if you have nematodes in your soil.

If you would like more information on growing tomatoes, please call your local Extension center and ask for guide sheet G6461, “Growing Home Garden Tomatoes.”  This guide sheet gives several suggestions for varieties that are resistant to some of the diseases which infect tomatoes.  You can also find it on the web at: