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More on Tomatoes


Sun, Aug 27th, 2000
Posted in

Monday, August 28, 2000

Was last weekís article enough on tomatoes? Almost, but not yet. A few more diseases of tomato that you should be aware of are Bacterial Spot, Verticillium Wilt and Fusarium Wilt. Remember when all tomato tags of hybrid tomatoes had the little letters VFN? These are the diseases were talking about. Except N, which stands for nematode, and thatís another article in itself. Now that open pollinated or heirloom varieties are becoming more popular, itís even more important that good cultural practices are followed to avoid seeing more of these diseases. Sometimes planting hybrids can make us a little less careful; tomatoes need all the special pampering we can give them to grow their best. See last weeks article for more specifics on care.

Bacterial Spot is a fungal type of disease. Symptoms are more noticeable on the fruit but also may be present on the leaves. Infected green fruits have slightly raised spots that are up to one inch in diameter and brown with rough surfaces. Ripe fruits will not be infected if disease onset is late. Most infection takes place during seedling stage and spreads to green fruit during wet weather.

In Fusarium Wilt, the first symptom is wilting of the oldest leaves. Frequently, the leaves on only one side of the stem turn yellow first, followed by yellowing and wilting of younger leaves and resulting in death of the plant. If plants are infected early in the growing season, and if warm air temperatures are rather high for an extended period, little or no normal fruit will be produced. Older plants infected with Fusarium wilt will sometimes produce normal clusters of fruit on the lower portion of the plants, but fruit produced in the upper portion will be small and inferior.

When a wilted plant is removed and the stem sliced near the soil line, a brown discoloration of the woody tissue can be seen between the pith and the outer, green part of the stem. The brown discoloration can extend to the top of the plant if wilting is severe.

Verticillium Wilt symptoms are yellowing of older leaves and wilting of young shoots during the day with recovery at night. Plants infected with Verticillium species are uniformly affected, whereas leaves of Fusarium-infected plants wilt and turn yellow on one side of the stem. Yellow blotches appear on the lower leaves; in time these areas turn brown, resulting in dead tissue. Infected plants are often defoliated and stunted and much of the crop is lost due to sunscald. Inspection of a sliced stem near the soil line will reveal brown streaks in the water-conducting tissue of the plant. However, unlike Fusarium, the discoloration rarely extends to the top of the plant.

Laboratory diagnosis is necessary to determine with certainty which organism is causing the disease.

Control of Bacterial Spot, Fusarium and Verticillium is difficult since both organisms can survive in soil for an indefinite length of time. Plants are infected in the seedling stage; spread to green fruits takes place during wet weather. Copper-containing fungicides help hold this spread in check.

Crop rotation of at least four to six years may be helpful for control of both diseases, but the most effective method is to plant disease-resistant varieties. These may be open pollinated or heirlooms or hybrids. Trials in your home garden may be the best method for you.
Extra Produce to Food Shelf

Do you have lots of extra produce? Baseball bat sized zucchini? Containers of carrots? Millions of melons or scores of squash? You can help neighbors less fortunate than yourself by donating to your local food shelf. They would love to receive your donation. Please call ahead, Preston area (507) 765-2761, Rushford area (507) 864-7741, Spring Valley area (507) 937-3350.

Virginia Cooper gardens and battles tomato blight from her farm in Mabel. She can be reached at the Extension office at (507) 765-3896, or via email: virgcoop@yahoo.com

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