It seems that the incidence of many tomato plant diseases depends on an area's climate. In my research, I also noticed that most of them are cause by fungus. Since I garden in the Pacific Northwest, early and late blight are my highest concerns. I avoid the fungus that causes these problems by:
Seven of the most common tomato plant diseases are described below with information on how to deal with them. They all seem to be caused by fungus so the 5 steps above would be a good start toward avoiding them. More specific info is including on each item below. This information comes from articles published in Organic Gardening Magazine.
Dark spots surrounded by concentric bull's-eye rings on the leaves. Fruits rot inside, starting at the stem. Seedlings may have dark, sunken-in spots around the soil line. This tomato plant disease is actually caused by a fungus that survives the winter on old vines. Clean up and throw away all debris after harvest, rotate crops and plant resistant cultivars. Avoid crowding and prune for air circulation.
Begins as yellow dots that quickly turn into brown zones surrounded by yellow halos. Cells in the center of the spots die and turn whitish. Remove infected leaves to contain.
Leaves take on a mottled yellow appearance and can lead to a stringy growth habit, particularly in cool weather. Transferred via infected plant material and affects many different types of plants. Avoid the use tobacco products while working with plants, and wash hands well prior to touching plants. Choose varieties denoted with a "T" on the seed package or plant marker to further reduce susceptibility.
Plants become wilted and limp (even well-watered ones). Leaf edges may curl and older leaves turn yellow in a uniform manner and start to die between the veins. Stems will have dark centers. Rotate crops. Remove and destroy all debris, do not plant tomatoes where the disease has occurred in the past. Select resistent varieties denoted with the initial "V" on the seed package or plant marker.
Starts as a downward leaf curl--older leaves yellow and die as the branch wilts. Symptoms may only appear on one section of plant. The stem may also have brown or black lesions, and inside there will be dark streaking. Common in the Southern United States. Rotate crops. Remove and destroy all debris, do not plant tomatoes where the disease has occurred in the past. Choose resistant varieties denoted with the intial "F" on the seed package or plant marker.
Produces dark spots on the leaves that turn brown and then papery. Late blight can cause the entire plant to collapse all at once and become a bad-smelling mess. Caused by a fungus that is favored by wet weather--the spores can travel great distances to affect plants. I've also heard that blight can happen after a sudden drop in temperature. Avoid crowding. Enhance air circulation within and among plants by staking or caging and by pruning. Keep leaves dry.
Watery, sunken spots on ripe fruits. A dark center with fungal spores may show up in the center of the sunken spot. Harvest fruit as soon as possible after ripening; remove and destroy severely infected plants. Clean up debris, control weeds and rotate crops.
Consider checking with local gardeners and the college extension service to find out what tomato plant diseases may be prevalent in your area so you can take steps to avoid them.
Common Problems Solved. April 2007. Organic Gardening Magazine.
8 Cagey Culprits. May 2003. Organic Gardening Magazine.
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