Gardening

Weather conditions can affect tomato fruit

By Dr. William M. Johnson, Galveston County Extension Agent - Horticulture

May 24, 2006

Tomato harvest is a highly anticipated event in our gardens. While tomatoes are not difficult to grow, some problems (such as fruit cracking, shown above) are more prevalent this spring due to soil moisture conditions.

Photo credit: William M. Johnson.

Texans have been pursuing the perfect tomato for a long time. Tomatoes are the most popular and most widely grown crop in home gardens across the state. In fact, nine out of 10 home gardeners try their hand at growing tomatoes.

If you garden, then chances are you are growing tomatoes this year. Neighbors will vie for the earliest, the largest, the tastiest, and the brightest red tomato on the block. And unlike the case when you start to experience an overabundance of squash from the garden, your neighbors and friends are not likely to lock their doors and close their curtains when they see you coming over with your surplus production of tomatoes.

While tomatoes are not difficult to grow, they are sensitive to extremes in environmental conditions and we’ve certainly had some notable extremes in weather this spring. Plant diseases can occur and fruit and foliage problems can be a challenge to manage.

Many common tomato problems are caused when environmental conditions are less than ideal for plant growth. In most cases, they will pass when growing conditions improve. The physiological effects on the tomato fruit, however, are determined by how long the unfavorable environmental factor lasts.

Since the primary causes of these problems are not insect nor disease related but rather are related to environmental conditions, they are usually referred to as tomato disorders (as opposed to insect and disease problems).

Temperature, plant nutrition, and soil moisture conditions are the most serious environmental factors that affect tomato fruit. Hence, fungicides and insecticides are of no help. Although it is possible for the gardener to make adjustments and corrections in plant nutrition and to some extent soil moisture, there's little we can do to control unfavorable temperature or weather conditions.

Here are some of the most common physiological problems or disorders that local tomato gardeners may experience over the season and some measures to take to avoid or reduce their occurrence:

CATFACE. This is the name applied to misshapen fruit with irregular bulges at the blossom-end of the fruit that may extend to the stem area. Catface is commonly found on first-formed fruits. This disorder is caused by an abnormal development of the flower pistil and is aggravated by prolonged cool weather during blossoming. Due to the unusually cool weather conditions of that occurred in April, don't be surprised to see a few cases of this disorder this spring.

LEAF ROLL. The edges of the leaves will roll or curl upward and inward in this common but temporary disturbance. In severe cases, rolling continues until the margins of opposite leaf sides touch. Growth of the plant is usually not inhibited.

Leaf roll is often a physiological response to an irregular water supply or will occur during bright sunny days following a period of cloudy weather. The leaf-roll syndrome is usually temporary and does not harm the fruit. Some tomato varieties are much more likely to develop leaf roll than others.

BLOSSOM-END ROT. This occurs under conditions of severe water stress and heavy fruit load. Blossom-end rot begins as a small, bruised-like area around the blossom-end of green or ripening fruit. Lesions darken and enlarge rapidly and become depressed and eventually black in color and leathery-like in texture. Usually, blossom-end rot occurs on the first fruits formed or on clusters of fruit formed during prolonged hot, dry periods.

Blossom-end rot is closely associated with moisture availability. This means that gardeners should try to avoid fluctuations in soil moisture during fruit set and fruit development. Mulching can be very helpful in stabilizing soil moisture around the plants.

Some references indicate that a calcium-deficiency contributes to blossom-end rot, but calcium is seldom deficient in our Upper Gulf Coast soils.

FRUIT CRACKING. It can be disheartening to find the fruit cracked and rotted after tending to the plants for an entire season. Either circular cracks or radial cracks (or both) develop at the stem end. The cracked areas are avenues for bacterial and fungal pathogens that cause fruit rots.

Fruit cracking is a common problem when a heavy rain occurs after an extended dry spell. Under these conditions, the interior of a fruit will typically absorb more water and expand at a faster rate than the skin (cuticle) of the fruit. Mulching and proper irrigation during dry spells will significantly reduce the occurrence of cracking.

SUNSCALD. This occurs when green or ripening fruits are exposed to hot sun for several days. A yellowish-white area of sunken tissue appears on the side of the fruit facing the sun. Sunscald on fruits is much more likely to occur after plants have suffered premature defoliation caused by disease, or during an extended period of cloudy weather followed by bright, hot sun. Avoid severe pruning of plants to provide adequate foliage growth to shade fruit from the hot afternoon sun.

Regardless of these and other problems associated with growing tomatoes, the tasty reward of having fresh, vine-ripen fruit makes all our gardening troubles worthwhile.

Dr. Johnson is a horticulturist with the Galveston County
Extension Office of Texas Cooperative Extension, Texas A&M University. Visit his web site at http://aggie-horticulture.tamu.edu/galveston/index.htm

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