It is about this time of year that I get several questions regarding diseases in vegetable gardens. The tomatoes are rotting. The bean leaves are wilting. Something looks stunted. The lower leaves are dying. The upper leaves are dying!
As we move away from our cool moist spring and into the heat of summer, the plants get older and all kinds of diseases tend to show up.
For years I have always been able to rely upon an old publication in our library printed in the early ‘80s called the “Plant Disease Handbook.” The book has been thumbed through for years and years. Sections such as St Augustine turfgrass and the tomato section are especially worn with use.
So, let’s take a look at the common diseases that affect tomatoes. There are no less than four pages in the book that outline diseases common to tomatoes in Texas. They include fungus, bacteria, and viral diseases in addition to nematodes and physiological disorders.
Control for all disease (and insect) pests is first accomplished by your actions of rotating crops, eliminating weeds next to your garden, cleaning up old garden plant debris, and, lastly, treating with a conventional or organic pesticide.
By far, there are more fungal issues than any other problems listed. Because the handbook is made for the entire state of Texas, it will often say a problem is caused by humid weather. Clearly, the author wasn’t’ from East Texas!
Some of the fungal problems specific to tomatoes include Late blight, Early blight, Gray leaf spot, Leaf-mold, Buckeye rot, Nailhead spot, Anthracnose, Fusarium wilt, Verticillium wilt, Gray mold, and Botryosporium Mold, to name a few. Molds are best prevented by crop rotation, eliminating crop residues from previous years, planting resistant varieties, and applying fungicides.
Have you ever seen a tomato variety given on a seed label with some letters following it? Often you will see hybrid tomato varieties on the seed packet followed by “V”, “F”, or “N”. These letters designate that the variety is resistant to Verticillium wilt (V), Fusarium wilt (F), or nematodes (N).
Bacterial problems include Bacterial spot and Bacterial canker. Virus problems include Tobacco Mosaic, Spotted Wilt, and Curly Top. Bacterial and viral problems are especially onerous as they are seed borne and can stay active in the soil for years. Control of these disease issues is best accomplished by starting with disease free seeds, rotating crops, and treating for insects.
Nematodes deserve special mention because they…truly are not a disease but will be listed in every ‘disease’ publication. Nematodes are microscopic roundworms. While there are a tremendous number of beneficial nematodes in our soil, the Root Knot nematode gets all the attention as it pierces the roots of many vegetable plants (including tomatoes) and clogs up the root system. Once you find them present in your garden, it is necessary to use a resistant vegetable variety.
Last, lets discuss a couple of physiological issues: blossom end rot and growth cracks.
Blossom end rot is a disorder that can appear on tomatoes at any time in their development, but most commonly appear when fruits are 1/3 to 1/2 grown. The initial symptoms appear as water soaked spots on the blossom end of the fruit. These spots later enlarge and become black. Secondary infection by other decay causing organisms will usually follow.
The cause of this disorder is considered to be a calcium deficiency in the developing fruit. Extreme fluctuations in soil moisture or excessive nitrogen fertilizer can also result in blossom end rot. The best means of control is to maintain a uniform soil moisture in addition to fertilizing with calcium at planting. ‘Tomato Rot Stop’ sprays at your local garden center can help alleviate the condition if caught and applied early enough.
Growth cracks can result from extremely rapid fruit growth brought on by periods of abundant rain and high temperatures especially following a period of dry weather. Cracks of varying depths will radiate from the stem end of the fruit, blemishing the fruit, and providing an entrance for decay causing organisms. Except by diligence of the gardener to keep the soil moist, no control measures are known.
If you’d like to see more information on these diseases and learn about many more issues that affect our gardens and landscapes, I’m happy to report that you can see the disease handbook online. In your search engine type in ‘Texas Extension plant disease handbook’. Following the links, you will be able to look at turfgrass problems, tree problems, vegetable problems, fruit diseases, and many more.