Why Are My Tomatoes Turning Brown?

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If you have tomatoes turning brown on the bottom then you are not alone. This time of year we have many calls about brown spots on tomatoes, squash, peppers, watermelons, etc. This is called blossom-end rot (BER), which is a nonparasitic disease of tomatoes and other fruiting vegetables.

The first symptom is a slight water-soaked area on or near the blossom end of the fruit. The affected area soon darkens and enlarges in a constantly widening circle until the fruit begins to ripen. The blossom end turns dark and has a dry, leathery appearance. With peppers the rot looks tan in color and can often be mistaken for sunscald, which is white in color.

The cause of this browning is due to the lack of calcium in the developing fruit. This comes from the lack of calcium uptake from the soil or extreme fluctuations in water supply. Extreme heat and humidity can also play a role in the development of BER. This year our tomatoes and other vegetables have been under tremendous heat stress and we are seeing more BER than we may be used to.

Sometimes there are no quick cures for things like BER. Often the plants tend to correct themselves, and as fruit is formed the problem subsides. If plants experience a quick rate of growth, do not receive uniform watering, or experience high temperatures, then we often see BER show up. There are preventive measures you can take to try to avoid BER. First, make sure you do a soil test to determine if the pH is between 5.8 and 6.2. If not, follow the report and apply the correct amount of dolomitic limestone in order to supply sufficient calcium to the plant. Another source of calcium would be gypsum or you can use calcium nitrate when fertilizing your plants.

Since BER is closely related to extremes in the water supply it is important to try to regulate the moisture supply to the plant. After plants are well established it is best to avoid disturbing the roots since tomatoes are shallow rooted plants. Mulching can aid in moisture retention and help maintain an even supply of moisture. In general, tomato plants need at least one inch of water per week either by rainfall or supplemental irrigation.

The removal of affected fruit will aid in the development of the remaining fruit on the plant. Other things to look out for on tomatoes at this time would be the tomato hornworm and the tomato fruit worm. Good luck with your tomatoes!

For more information about tomatoes or vegetable gardening, contact your local N.C. Cooperative Extension of Franklin County office at 919-496-3344.

Blossom End Rot Tomato

Blossom End Rot on Tomato

Tomato Hornworm

Tomato Hornworm

Tomato Fruit Worm

Tomato Fruit Worm