Diseases Cause Problems With Homegrown Tomatoes
Keith Hansen
If you have a backyard vegetable patch, chances are good that tomatoes occupy a prominent place in the garden.
Homegrown tomatoes are so tasty and good for you too, being very high in the beneficial antioxidant lycopene. Just a few well-grown tomato plants can produce enough to easily feed a family.
So, red flags are quickly raised when the fruit or plants don't look right or start having problems. Rotting fruit and yellowing foliage are two common tomato complaints.
We've already had several inquiries concerning tomatoes with black spots on the bottom of the fruit, which translates into Blossom End Rot. The black or dark spot which appears on the blossom end or bottom of the fruit is usually not soft or mushy, but a somewhat firm rot. Decay going up into the center of the fruit will be a dry rot, unless the fruit is also touching the ground, allowing other rotting organisms to enter the fruit.
Blossom end rot is not caused by a fungus or other disease-causing organism.
The problem stems from a calcium deficiency in the developing fruit. But, it is brought on by fluctuating soil moisture levels, root pruning and/or excessive nitrogen fertilization, lack of calcium in the soil, or a combination of these factors.
Eggplant and melons can also occasionally suffer from blossom end rot.
Blossom end rot can occur at any time during fruit development, but is most common when fruits are one-third to one-half grown (or just turning ripe), usually in early June.
Large-fruited tomatoes, especially types that are somewhat flattened on the bottom, are much more seriously affected than smaller types. Come to think about it, I don't recall ever seeing blossom end rot on cherry tomatoes.
Abundant, soaking rain, interspersed with dry conditions, occurring during fruit development is usually responsible for this problem. Even for folks with sandy soil, if the tomatoes are grown on the flat, the soil can get waterlogged for a short period of time which can be long enough for problems to start. This is why tomatoes are often recommended to be grown on raised beds or on hills rather than on the flat.
What can you do about blossom end rot? Since it is not a pathological disease, the problem must be addressed through cultural practices.
First, pick off all of the affected fruit. The best control for blossom end rot is to maintain a uniform supply of moisture through irrigation and mulching. Mulching will keep the soil more uniformly moist during dry periods. And, as mentioned above, provide cultural conditions that allow for good drainage. Raised beds or rows are ideal. Avoid prolonged wet/dry cycles.
Also, do not deeply cultivate the soil around the plants while weeding. This can destroy tender roots and therefore interfering with water uptake. Excessive nitrogen fertilization can also combine with other factors to create conditions favorable for blossom end rot development.
You might try adding gypsum or agricultural limestone the next time you prepare the soil before planting to provide a source of calcium.
Ag lime or dolomite lime will raise the pH, and should be added based on results of a soil test to correct strongly acidic soil. Gypsum does not affect the soil pH. Commercial products are available for spraying calcium (calcium chloride or calcium nitrate) if blossom end rot symptoms appear. Be careful, though, because these products, especially calcium chloride, can burn foliage under hot conditions. Calcium sprays are not a substitute for proper irrigation and fertility management.
The good news is that the next set of tomatoes to ripen should be okay provided the plants' water needs are met.
Another tomato problem we occasionally see is plants showing excessive twisting, curling and deformed shoots and leaves. This could be either one of the tomato viruses, or exposure to hormone-type broadleaf herbicides.
One way to determine whether these symptoms are caused by disease or herbicide injury is to see what percent of the plants are affected.
One plant here and there randomly affected would indicate a viral disease, whereas a whole block or row of tomato plants affected would point to herbicide injury.
There is nothing that can be done for virus-infected plants other than to pull them from the garden to prevent the further spread of the disease. Herbicide injury can be from direct exposure to drift, or, as has often been the case, from hay or grass used as a mulch from a pasture or lawn recently treated with broadleaf herbicides. Even manure can be the source of herbicide if the cattle had recently grazed treated hay.
Keith Hansen is Smith County Horticulturist with Texas AgriLife Extension Service.
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