As with any garden season there can be some issues and this year is not any different. There have been several intense rainstorms, very cool weather at times, and extreme heat and humidity at other times creating conditions to promote certain diseases.

Lately, most of the phone calls I have received are about tomato issues. So, I thought I would share some of the more common diseases that may be affecting tomatoes.

Bacterial Wilt is a serious disease. This bacterium survives in the soil for extended periods and enters the roots through wounds made by transplanting, cultivation, insect feeding damage, and natural wounds where secondary roots emerge.

Disease development is favored by high temperatures and high moisture. The bacteria multiply rapidly inside the water-conducting tissue of the plant, filling it with slime. This results in rapid wilt of the plant while the leaves stay green. If an infected stem is cut crosswise, it will look brown and tiny drops of yellowish ooze may be visible.

Control of bacterial wilt of plants grown in infested soil is difficult. Rotation with non-susceptible plants, such as corn, beans, and cabbage, for at least three years provides some control. Remove and destroy all infected plant material. Plant only certified disease-free plants. Chemical control is not available for this disease.

Early Blight is first observed on the plants as small, brown lesions mostly on the older foliage. Spots enlarge and concentric rings in a bull’s-eye pattern may be seen in the center of the diseased area. The tissue surrounding the spots may turn yellow. If high temperature and humidity occur at this time, much of the foliage is killed.

Lesions on the stems are similar to those on leaves and sometimes girdle the plant if they occur near the soil line. On the fruits, lesions attain considerable size, usually involving nearly the entire fruit. Concentric rings are also present on the fruit. Infected fruit frequently drops.

Use resistant or tolerant tomato cultivars and use pathogen-free seed. Use crop rotation, eradicate weeds and volunteer tomato plants, space plants to not touch, mulch plants, fertilize properly, don’t wet tomato foliage with irrigation water, and keep the plants growing vigorously.

Trim off and dispose of infected lower branches and leaves. If the disease is severe enough it can respond well to certain fungicides.

Septoria Leaf Spot can be a destructive disease of tomato foliage, petioles, and stems (fruit is not infected). Infection usually occurs on the lower leaves near the ground, after plants begin to set fruit. Numerous small, circular spots with dark borders surrounding a beige-colored center appear on the older leaves. Tiny black specks, which are spore-producing bodies, can be seen in the center of the spots.

Severely spotted leaves turn yellow, die, and fall off the plant. The fungus is most active when temperatures range from 68 to 77° F, the humidity is high, and rainfall or overhead irrigation wets the plants. Defoliation weakens the plant, reduces the size and quality of the fruit, and exposes the fruit to sunscald. The fungus is not soil-borne but can overwinter on crop residue from previous crops, decaying vegetation, and on some weeds related to tomato.

Most currently grown tomato cultivars are susceptible to Septoria Leaf Spot. Crop rotation and removal of crop debris will reduce the amount of inoculum. Do not use overhead irrigation. This disease does respond to fungicide treatments.

Blossom End Rot is a physiological disorder of tomato. Symptoms are water-soaked spots on the blossom end of the fruit. These spots enlarge and become black. Secondary infection by decay-causing organisms usually follows.

The cause of this disorder is a calcium deficiency in the developing fruit. In Most cases, extreme fluctuations in moisture, rainy or cloudy weather with high humidity, cool temperatures are the primary causes but insufficient soil calcium, root pruning from nearby cultivation, and excessive (NH4 +) nitrogen, potassium, or magnesium fertilization can also increase the chances of blossom end rot, especially early in the season.

Maintaining a uniform supply of moisture through irrigation and adequate soil mulches can prevent this. Mulches will not only keep the soil cooler and more evenly moist but will suppress weeds, thus reducing the need for nearby cultivation that may damage tomato roots. Remove fruit with blossom end rot symptoms from the plants.

Fusarium Wilt is a warm-weather disease. The first indication of disease in small plants is a drooping and wilting of lower leaves with a loss of green color followed by wilting and death of the plant. Often leaves on only one side of the stem turn golden yellow at first. The stem of wilted plants shows no soft decay, but when cut lengthwise, the lower stem will have a dark brown discoloration of the water-conducting vessels.

The fungus is soil-borne and passes upward from the roots into the water-conducting system of the stem. Invasion occurs through wounds in roots growing through infested soil. Long-distance spread is through seed and transplants. No chemical control is available.

There are certainly other diseases that can impact tomatoes, but these would be the more common that we see year to year.

As always, good management and scouting can help in diagnoses and control. I hope you find this information helpful and you have a successful harvest from your gardens.

If you have any questions, feel free to email me at [email protected] or call the Clinton County Extension Office at 937-382-0901.

Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for over 30 years, currently serving Clinton County and the Miami Valley EERA.