Black Spots on Tomato and Lettuce

Q. I have six tomato plants grown from seed, all indeterminate. They were growing in two-year-old, rich soil mix containing compost that produced a lot of tomatoes last year. The leaves of the tomato plants developed okay but then they got spotty and dried up. No blossoms at all. The leafy vegetables grew well but the older leaves at the bottom of lettuce also developed black spots, became yellow and died.

This gardener has been growing tomatoes this gardener has been growing tomatoes for over 30 years in the Las Vegas Valley. He seems to favor Celebrity but he grows them in the same spot year after year. We've got to learn to rotate vegetables so they are not grown in the same spot year after year.

A. I looked at the pictures you sent. Tomato diseases are tough to diagnose with pictures but I think this might be bacterial leaf spot. I first got suspicious when you said you started these plants from seed. Then I considered the wet, cool weather, which is perfect for this disease to develop, and concluded it was probably bacterial leaf spot. 

Bacterial leaf spot in North Carolina

Tomato disorders from Iowa

Google some pictures of this disease on tomato and lettuce and see if you think it looks like the same and let me know. Leaf spot diseases such as bacterial leaf spot can occur on lettuce as well.

Google pictures of bacterial leaf Spot

            Leaf spot diseases can infect the plant from seed contaminated with this disease agent. Most seed will have this disease present so applying a hot water or chlorine seed disinfection helps reduce this disease possibility. Methods for doing this at home can be found on the Internet or I can forward instructions to you.

            Cool and wet weather, perfect weather for this disease, promotes bacterial leaf spot if it’s present. This disease can become a problem if the growing area has not been cleaned up and old fruit and fines are present. 

Also, don’t grow vegetables in the same location year after year (implement crop rotation) to reduce the possibility of this disease, and several others, from occurring. Crop rotation can be as simple as not growing the same vegetable in the same location in a raised bed year after year.

            Indeterminate tomatoes have vines that keep getting longer and longer while determinate tomatoes produce short vines and flower sooner. For earlier production of tomatoes, choose determinate tomatoes rather than indeterminate ones. 

Determinate tomatoes are better for most home gardens in the hot desert anyway because you want to produce tomatoes as quickly as possible. Hot weather can come quickly and air temperatures above 95F can stop tomatoes from forming from the flowers.

            If you select indeterminate tomatoes, and then fertilize them with high nitrogen fertilizers, the plants will grow beautifully but produce few flowers until they get older. When growing indeterminate tomatoes, don’t fertilize plants after planting until they begin to bear fruit.