Heat Stress on Vegetables

The past few weeks I have found and harvested several ugly and distorted tomatoes from my garden. What aren’t my vegetables pretty?

Many of the vegetable problems facing homeowners and farmers in mid-summer are likely weather related and are considered environmental disorders, not diseases. The extreme heat and lack of rainfall typical of July and August can be to blame for some things and greatly affects late season growth and flowering production. However, many of the cosmetic flaws found on the fruit to be harvested may be attributed to drastic changes in temperature and moisture levels during flowering and as well as during fruit development.

Catfacing and rough blossom scars are commonly seen on home-grown tomatoes giving them an imperfect appearance. Catfacing is the term used to describe fruit with deep indentations in the blossom end or fruit with significant distortions. According to Dr. Joe Kemble, Extension Specialist, these problems are more serious with large-fruited varieties than they are with cherry or Roma tomatoes. These disorders are more prevalent if the weather is cool and cloudy at the time of bloom. Unfortunately there is little that can be done for control of catfacing, except selecting varieties that are not prone to the problem.

Cracking fruit is another common environmental disorder found on tomatoes that really frustrates home gardeners at harvest. Dr. Kemble states there are two distinct types of fruit cracking: radial and concentric. Radial cracking is the most common and results in the most fruit damage. Cracking occurs when internal expansion is faster than the expansion of the epidermis, causing the outer skin to split. It occurs more often during rainy periods when the temperature is relatively high, especially when rains follow a long, dry period. Radial cracking can occur at all stages of fruit growth but as fruit mature they become more susceptible, especially as color develops. Concentric cracking begins on green fruits that are fully exposed to the sun. Maintaining a uniform water supply throughout the growing season with drip irrigation, mulches, or both, and maintaining good foliage cover will help reduce fruit cracks.

Other late season woes are probably from heat stress. Mature tomato plants suffering from such stress may produce small fruit, hold its fruit on the plant but not enlarge, or drop its flower blossoms. Regular watering and general care may help improve the situation but it may be best to start new young plants around mid summer for fall harvest rather than relying on the poor vigor of an old and depleted tomato plant. Planting heat resistant varieties of tomatoes is also recommended and worth trying.

For help on other home and garden questions, call the Master Gardener Horticulture Helpline at 1-877-ALA-GROW (1-877-252-4769) or visit us online at www.aces.edu.