Archive for Thursday, June 29, 2006

Preserve your bountiful tomato harvest by fighting disease, rot

June 29, 2006


There is nothing more delicious than fresh salsa made from vine ripe tomatoes harvested from the garden. And there are few things more disappointing than having to throw away tomatoes because they are spotty, malformed or have a dark patch on the blossom end. Now that we are entering tomato harvest season, gardeners are starting to inspect their crop a bit more closely. Unfortunately, what they are finding is less than desirable. Here is what you can do to stop the rot and disease and enjoy a bountiful tomato harvest the remainder of the summer:

The brown leathery patch on the bottom or blossom end of the fruit is called blossom-end rot. It is not caused by a disease, and chemical sprays will not stop it. It is the result of a nutritional imbalance in the fruit - more specifically a calcium deficiency. Calcium is an important nutrient in the development of tomato fruit. Although there is usually an ample supply of calcium in garden soil, it is not always available for fruit development. Warm spring temperatures cause rapid top growth with limited root growth. As the plant pulls calcium from the soil, it moves the nutrient in the water stream from roots to tops, bypassing the fruit and causing the deficiency. As the plant acclimates to summer weather, tops slow down and roots enlarge, bringing the plant back into balance. Available calcium then can be used for fruit development. Blossom-end rot usually disappears on later fruit.

The best way to stop blossom-end rot is with water. Keep the soil uniformly moist throughout the growing season. Plants that have water are able to take up and move needed nutrients more easily. Next, do not overfertilize. Plants that are excessively lush because of overfertilization are usually more prone to developing blossom-end rot. Slow, sustained growth is better than fast, forced growth. Finally, be patient. Although the first fruit to set does not develop normally and is not very appetizing, eventually, the plant will work the problem out, and you will harvest beautiful, full tomatoes.

There are two leaf diseases that will need to be controlled as well. Septoria leaf spot causes small, brown to black lesions, while early blight results in larger, target-shaped spots. Infected foliage turns bright yellow, then brown and eventually drops from the plant. They initially attack the lower, inner foliage, then progress up the plant, killing more and more leaves. The plant may not die completely, but tomato production is greatly reduced.

Leaf spots can be suppressed by a combination of cultural and chemical methods. Because both diseases overwinter on dead plant debris, a complete cleaning of the garden area is a must. Next, stake or cage plants to increase air movement and reduce conditions favorable for fungal infection. Use straw mulch around the base of the plants to help prevent splashing water from spreading the disease. When watering, only wet the soil around the plant, and try to keep the leaves dry. Wetting the leaves late in the day, coupled with dew formation at night, increases the number of hours the leaves remain wet and increases the chance of getting fungal infections.

Control weeds in the garden. Not only do they compete for moisture and nutrients, they crowd the tomatoes, increasing humidity and blocking air flow. Finally, use fungicides. Applications every seven to 21 days will help slow or even stop the progression of these fungal diseases. Begin applications as soon as the first leaf spots are noticed. Do not wait until you see heavy leaf spotting because it is difficult to stop the disease at that point. Products that have Chlorothalonil as the active ingredient, such as Fertilome Liquid Fungicide and Ortho Liquid Fungicide, work well. Other products to consider are Daconil, mancozeb and copper-based products like Bordeaux. If rainfall washes off the fungicide, you will need to reapply. As always read and follow all the label directions.


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