Ask a Specialist: What is wrong with my tomatoes?
Answer by: Taun Beddes, Utah State University Extension horticulture agent, Cache County
Many gardeners have waited all summer to eat fresh tomatoes. Sometimes though, as the first tomatoes mature, they may be deformed, cracked or somehow have problems. In this case, the weather, not microorganisms, is usually to blame. Four conditions are especially common. These include sunscald, cat-facing, cracking and blossom end rot.
Consider this information.
*Sunscald appears on fruit as a white or yellow patch and is usually found during hot, dry weather. It is especially common when tomato plants are pruned and underlying fruit is suddenly exposed to the sun. There is no foolproof way to prevent sunscald. However, avoiding pruning in mid-to-late summer will help. Additionally, keep foliage as healthy as possible. Sunscald is also common on peppers.
*Cat-facing is a condition that looks like something scratched and damaged the bottom surface of the tomato when it was young and then the tomato scarred over and continued to heal. This condition is caused by extreme temperature fluctuations when the first tomatoes were set earlier in the season. The damaged area can be cut off, and the tomatoes are fine to eat. The condition usually disappears later in the season.
*Cracking occurs when the skin of the tomato is not elastic enough to handle its growth rate. It can occur either horizontally or vertically on the fruit. It is especially common with alternating periods of cool, wet weather and hot, dry weather. Additionally, it is common with faster growing plants and with certain varieties. Over-fertilization and sporadic watering can also cause cracking. For prevention, keep tomatoes evenly moist and do not over fertilize. As with cat-facing, damage can be removed and the tomatoes can be eaten. Smaller tomatoes, such as grape and cherry tomatoes, seem to crack less often than larger varieties.
*Blossom end rot is usually caused by conditions that disrupt calcium uptake in the root-zone of the plant such as abnormally cool weather, irregular irrigation and infrequent summer rainstorms. The condition occurs on the bottom of the tomato's base where a dry rot occurs and the flesh takes on a leathery feel and turns black or brown. More than half of an individual fruit may be affected. Blossom end rot can be prevented by keeping the root zone of plants evenly moist. Allowing the soil around roots to dry too much and then deeply irrigating can cause the rot. Mulch placed around plants helps keep water from evaporating from the soil too quickly and can prevent blossom end rot. Various sprays labeled to prevent or mitigate the condition are available at garden centers, but these sprays are not usually effective.
The best prevention is to irrigate correctly. Blossom end rot can also occur in other plants, such as peppers and eggplant.
Direct column topics to: Julene Reese, Utah State University Extension writer; 435-797-0810 or Julene.firstname.lastname@example.org.