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Wheeler: Preventing blossom-end rot in tomatoes

POSTED: May 4, 2012 1:30 a.m.

I know it is a bit early in the season to be talking about tomato fruit diseases, but blossom-end rot is a disease that can be prevented with a little TLC.

Blossom-end rot is a symptom of calcium deficiency in tomatoes, which may be caused by low soil calcium, low levels of calcium in the fruit, or other factors like fluctuating soil moisture.

In tomatoes, decay is visible on the blossom end. The initial symptom of the disorder is a small darkened or water-soaked area around the blossom end of the fruit, appearing when the tomato begins to ripen.

As the tomato matures, the spot darkens, enlarges and becomes sunken. Over time, the affected area becomes infected with other diseases, which may cover the initial signs of blossom-end rot.

The calcium deficiency producing blossom-end rot is mostly a result of climatic or cultural problems. It is related to several factors, including calcium, nitrogen, and soil moisture levels.

Even if you have adequate calcium levels in the soil, moisture stress will cause most of the calcium to be deposited in the leaves and not in the fruit, where it is needed to help form the skin of the tomato.

Prevention of blossom-end rot is the best route to take because it is almost impossible to correct once it has occurred. Spraying calcium on the leaves will not correct blossom-end rot once it has appeared.

Cultivars that grow quickly and produce large amounts of foliage tend to be more susceptible to the disease. Reducing the amount of nitrogen used may help reduce blossom end rot as well.

The use of 1-2-3 or 1-2-2 ratio fertilizers in place of 1-1-1 ratio fertilizers will help balance the level of nitrogen with other nutrients, especially calcium. Examples of fertilizers to use are 6-12-12 or 5-10-15.

Here are just a few things to keep in mind to help prevent blossom-end rot:

Select sites that have deep, well-drained soils. A large, well-formed root system will allow the plant to take up more calcium and other minerals.

Make sure to maintain a soil pH of 6.0-6.5. Check the calcium level in your soil every year. This is easily done by testing your soil through our office.

Mulch plants to conserve moisture and to provide a uniform water supply. Mulching may also prevent soil borne diseases by keeping soil from splashing up on the leaves and lower stems of the plants.

Avoid severe pruning and keep the plants well watered. Plants typically require 1-1 « inches of water per week during the summer. Remember to water deeply and less often to promote good root growth.

Pruning encourages the plant to put a lot of resources into growing new stems and leaves, not fruit.

Michael Wheeler is county extension coordinator for the UGA Cooperative Extension in Hall County. You can contact him at 770-535-8293, www.hallcounty.org/extension. His column appears weekly and on gainesville times.com/life.


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