Since tomatoes are the favorite crop of home vegetable gardeners, it comes as no surprise that they are frequently vexed by tomato troubles. Many of these woes are abiotic disorders. This means that they are not caused by insects or plant diseases. Most abiotic problems are related to weather, watering, soil fertility, or other gardening practices.
Blossom End Rot: Blossom end rot on tomatoes is arguably the most common disorder that bothers gardeners. Blossom end rot first appears as a brownish water-soaked area on the blossom or bottom end of the tomato. This area develops into a dry, brown, leathery lesion as the fruit matures and ripens. Blossom end rot can also show up on other veggies including peppers and eggplant. While “rot” seems to imply it is a fungal disease, it is actually caused by low levels of calcium in the fruit.
In some regions of the country, the underlying cause of blossom end rot is low levels of calcium in the soil, but most of our local soils have plenty of available calcium. When blossom end rot shows up here, it means that something, usually a water imbalance, has interfered with the uptake of calcium. Persistently very wet soil or very dry soil or widely fluctuating soil moisture are often the true cause of blossom end rot. Other practices that can be at fault include planting early in the season before the soil warms up, high nitrogen levels in the soil, restricted roots, or root damage from cultivating too close to the plants.
Thankfully, blossom end rot tends to only effect the earliest fruit of the season. However, it is best to always keep your garden soil evenly moist. You should also avoid planting your tomatoes early in the spring when the soil is still cold, even if you can provide the plants with frost protection. When planting tomato transplants, be sure to loosen the roots in the root ball so they do not stay root bound, and be careful when cultivating near your tomatoes.
Fruit Cracking: Longitudinal cracking or the splitting of tomato skin occurs when the inside volume of the fruit is expanding faster that the skin can grow. These cracks typically start at the stem and move downwards. A rapid uptake of water by the fruit after heavy irrigation or rain, especially when the soil was very dry, is usually the cause of the problem. Fruit is more apt to crack when excessive nitrogen fertilization has promoted lush growth. Tomato plants with a light crop or with fruit exposed to direct sunlight are also predisposed to developing cracks. Plus, certain varieties of tomatoes are prone to cracking.
To prevent cracking, keep the soil evenly moist, do not heavily prune or fertilize your tomato plants, and select crack-resistant varieties.
Sunscald: Sunscald or sunburn of a tomato is sometimes confused with blossom end rot. However, sunscald shows up on the side of the fruit exposed to the sun and initially appears as a whitish to tan area that later turns leathery. Sunscald tends to occur when fruit are at the mature-green stage or when they are just starting to show some color.
While sunscald is most common with peppers, it also occurs on tomatoes. It happens because skin tissues are killed from sudden exposure to sunlight or from tissue-killing temperatures caused by high heat and intense sunlight.
Maintaining adequate foliage to shade the fruit provides the best defense against sunscald. This can be accomplished by keeping the plants healthy and by not pruning the plants.
Blossom end rot, fruit cracking, and sunscald are the most common abiotic disorders you will encounter in your efforts to grow delectable and luscious tomatoes. The good news, is that by maintaining healthy plants with proper watering and fertilizing and by not pruning your tomatoes, you can usually avoid these problems.
For more information on tomato problems in local gardens go to bit.ly/TCHtomprob.
Marianne C. Ophardt is a retired horticulturist for Washington State University Benton County Extension.