Why are some (not all) of my tomato forming black ulcers?

by Dwight Cosper
(Philadelphia, PA)

Q. I was very successful last year: 210 lbs of bright red, edible fruit in a patch only 5 feet by 14 foot behind my apartment. This year I have staked plants all plants (last year about half of plants thus staked), so they must grow vertically, not horizontally. I apply Miracle Grow fertilizer every two weeks. At the beginning of the season, before planting, I applied mixed potting soil and time release fertilizer.

All vines are healthy, and about five feet tall now. However half of fruit being produced has black ulcers leading to very soft or rotten fruit, and half is perfect. How can I treat fruit to prevent further loss of fruit?

A. From your description, sounds like your plants are suffering from one of two conditions: either blossom end rot (BER), a common tomato problem associated with growing conditions, or anthracnose, a fungal disease.

Tomatoes impacted by BER suffer from a calcium imbalance. Even if the soil has adequate calcium, plants struggle with even uptake. Tomatoes absorb calcium through water. But calcium isn’t fast-moving. If a tomato grows quickly, or if other conditions slow water absorption, then calcium doesn’t have enough time to travel through the whole piece of fruit. Tissues break down and leave dark, leathery spots on the tomato's blossom end - the part of the fruit furthest from the stem end, to which water must travel furthest.

Several conditions can contribute to BER: inconsistent watering/rain, extreme temperatures (too hot or too cold), too much nitrogen or too many salts in the soil, and pH imbalance (soil too acidic or too alkaline). Plants are especially susceptible to BER when fruit is developing or even mid-size.

How to deal with BER
Make sure plants are watered consistently.

You can preserve affected plants by applying calcium immediately. You can use these natural products specifically developed to treat, prevent, and slow blossom end rot in tomatoes: Enz-Rot Blossom End Rot (a concentrate that can make up to 8 gallons) and Tomato Rot-Stop (in a ready-to-use spray bottle.) Follow package directions for application.

Another possibility: Anthracnose
Your tomatoes could be affected by anthracnose. Look for small, watersoaked, circular, sunken, dark spots under the skin of fruit as it ripens. While BER forms on the blossom end of tomatoes, anthracnose can affect tomatoes on any part of the fruit. Spots can develop jelly-like ooze, splitting with excessive bruising, and soft decay. Maturing and ripe fruit are especially vulnerable to developing anthracnose. The disease is caused by a fungus. Treat plants with a biofungicide like Serenade, beginning just as plants form fruit.

Good luck and happy gardening!
Your friends at Tomato Dirt