By Janice Gestner, Master Gardener
Tomatoes (Solanium lycopersicum) are among the most commonly grown vegetables by gardeners. The joy of using vitamin-rich, low-calorie tomatoes in fresh summer salads, in sauces, and many more ways make it one of the most versatile vegetables grown. The easiest way to avoid tomato problems is by giving them the site, space, and conditions they want as a plant that originated in South America. Tomatoes along with its Nightshade family members, including eggplants and peppers, love the sun-filled days with temperatures between 65°F and 95°F. They love well-drained, fertile soil, pH numbers between 5.5-7, mulches to regulate soil temperatures and moisture, and plenty of space. Cages, stakes and careful pruning help keep plants clean and less prone to disease. Consistent watering until tomatoes are ripening is also important to overall plant health.
Gardeners who carefully follow all of the growing tips for tomato plants will avoid many of the disease and insect issues that can be problems for tender tomato plants. However, sometimes climate conditions, gardening errors, insects and other problems happen. The University of Minnesota Extension site titled “Tomato Disorders” at https://extension.umn.edu/plant-diseases/tomato-disorders provides information about possible disorders. A summary of the information found on this site includes the following:
- Disorders may be caused by varietal choices. If gardeners have provided good management, trying different tomatoes varieties might be the best answer for the location. Seed catalogs can give information on disease resistant varieties.
- Blossom-end rot is an issue where fruit has a tan/black flattened spot on the end of the fruit. This is usually caused by inconsistent watering or possibly too heavy rains. The plant has a calcium deficiency that is not usually caused by soil deficiency but the inability for the plant to take up calcium through the roots. Gardeners should remove all tomatoes with the disorder because they will never develop correctly. New fruit coming on the tomato plant may be okay if watering is carefully controlled.
- Sunscald can be seen on tomatoes that have a pale yellow or white side surface. It is caused by too much sun, the result of leaf loss due to over-pruning, insect damage or disease damage. The spots can be an entry point for decay, and tomatoes should be picked immediately since they will not develop properly. Continue to harvest developing tomatoes.
- Early blight is caused by either of two pathogens called Alternaria tomatophila and Alternaria solani. They attack the plant either by being blown in on the wind, splash up from contaminated soil, humidity, wet weather, or even from human contact. They usually start at brown spots on the lower part of the plant. Safe practices to avoid the contamination include watering low to the ground and adding mulch around the plants to avoid soil splash up. Prune away any leaves on the low part of the plant that you see with brown spots. It is okay to remove up to a third of the bottom leaves if necessary. Be sure to wash your hands and clippers to avoid passing the fungus on to other plants.
- Growth cracks circling the stems on tomatoes may happen because of fast growth. Heavy rains and high temperatures can also cause these cracks. Regulating watering is the best way to try to avoid the condition. Tomatoes can be used if you cut off the cracking area and use the rest of the tomato.
Healthy tomato plants depend upon us to provide the best growing conditions we can provide as described above. Remember to rotate tomato crops to other sunny sections of the garden to avoid leftover pathogen and tomato problems from past years. Last, sometimes gardeners do everything correctly, but weather conditions may still control the harvest outcome. There is always a new year to try again.
You may want to watch the YouTube video about tomato problems.