Ask the Expert: What disease do my tomatoes have and how do I manage it?

Editor’s note: Throughout the growing season, Mike Hogan, OSU Extension educator for Agriculture and Natural Resources in Franklin County, will answer gardening and home landscape questions submitted by Dispatch readers. Send your questions to hogan.1@osu.edu.

Q: My tomatoes have ripened but have black and brown shrunken areas on the bottom. How can I control this disease?

A: The condition which you describe is called blossom end rot, which is actually a physiological condition, not an infectious disease. Blossom end rot is associated with a low concentration of calcium in the tomato. A fair amount of calcium is needed for the fast-growing tomato to develop normally, and when calcium demand exceeds supply, the tissues break down and the shrunken, dry, leathery, black areas develop on the blossom end (bottom) of the tomato. This condition can also occur on the shoulder and sides of the tomato.

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This is a fairly common condition even when the level of calcium in the soil is adequate to support vegetable growth. This condition typically results from drought stress, excess moisture, or most commonly from fluctuations in soil moisture levels. Typically, the condition affects only the first tomatoes of the season. This condition can also occur in peppers and eggplant, usually on the sides of these vegetables.

To minimize this condition, be sure to water small amounts frequently as opposed to letting the soil dry out completely and then soaking the soil. And be sure to water the soil directly, not the foliage of the plants. Mulching bare soil will help moderate soil moisture as well.

While calcium deficiency in the plant is the cause of this condition, simply applying calcium to the foliage of the plant does not solve the problem if the plant remains under stress. Calcium is relatively insoluble and plants under stress cannot move it to flowers and developing fruit.

Q: While sitting on my deck last night I saw a huge, lime-green-colored, moth-like insect with purple eyes and a purple border on its wings. Is this insect harmful?

A: That sounds like a luna moth (Actias luna), which can have a wingspan of 3-4 inches. The luna moth is in the giant silkworm moth family and is native to the eastern half of the U.S. and southeast Canada. It can be difficult to spot these moths as their color allows them to blend in among the foliage of host trees such as oak, poplar, walnut, cherry, elm, and others.

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Like most moths, luna moths are nocturnal (predominantly active at night). Adult luna moths only live for a week to 10 days while they locate a mate and reproduce. Adult luna moths do not feed or pollinate plants and are not harmful at all. Owls, hornets, and parasitic wasps are predators of luna moths.

Q: Many of my flowers were damaged by hail last week and the leaves have turned brown. The leaves on a small dogwood tree that I planted this spring are completely shredded. Should these plants be pulled out or will they eventually recover?

A: Damage from recent hail episodes has been very spotty in Greater Columbus, with the worst damage occurring in northeast Columbus and portions of Gahanna. Many plants began to bounce back just a couple of days after being damaged by hail. Plants with larger leaves seem to be damaged the most. I have seen elephant ears and cannas decimated by hail. Plants with smaller leaves such as petunia and ferns weathered the hailstorm without damage.

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Remove plant debris, broken stems and dead leaves. For larger leaves, snip off the shredded portions. An application of a low-nitrogen fertilizer can promote new growth and help plants bounce back. Be sure to provide supplemental irrigation if adequate rainfall does not occur.

The dogwood should be fine if the leaves are still green, which means that they can still turn sunlight into energy for the plant through photosynthesis.