Horticulture News: As tomato harvest time nears, some issues arise

By Kim Cowherd Published:

Tomato time is almost here!

Many home vegetable gardeners will begin harvesting this tasty fruit soon and there are beginning to be local field-grown tomatoes to choose from at the Farmers Market, produce stands and roadside stands.

I am beginning to get questions regarding tomato plant and fruit problems coming into the Extension Office. Dr. Tim Coolong, University of Kentucky Vegetable Specialist, talks to us about some of the problems that we may encounter with growing tomatoes and how to prevent these.

Coolong’s comments

Tomatoes are susceptible to a variety of non-pathogenic (non-disease) fruit disorders.  These disorders are not infectious, but are generally the plant’s response to adverse environmental conditions.  Some non-pathogenic disorders can be corrected by adjusting water, temperature, or shading.

Others are not fully understood or may be an interaction of genetic and physiological problems that are difficult to correct.  Cultivars vary in their susceptibility to these non-pathogenic disorders.

Cool temperatures are a contributing factor to some tomato disorders, such as catfacing and puffiness. Other non-pathogenic tomato disorders are related to nutritional imbalances or deficiencies in the soil. Some problems can be started by high humidity, an over abundance of rainfall, or high temperatures. Disease often is a secondary problem, following the initial issues begun with environmental conditions.

Common organic soil management practices can reduce the risk of some of these disorders.  Organic amendments and mulching can reduce the magnitude of soil moisture fluctuations, an important contributing factor to blossom end rot and cracking.  Adding organic matter, such as compost, will aid in tomato plant health.

The following are some common problems tomato growers may encounter as the fruit ripens. Knowing about these problems in advance of fruit set, may help you correct deficiencies ahead of time so that the tomatoes may have the best chance of normal development.

Common problems

Dark brown or black sunken areas at the blossom end of the fruit characterize blossom end rot.  The lesions are a direct result of a localized calcium deficiency at the blossom end. Although calcium deficiencies are sometimes responsible for blossom end rot, much of the time, blossom end rot is the result of plant water stress.  Calcium moves primarily in water-conducting tissues of the plant so when water movement is restricted, calcium deficiencies develop.

Regular watering that avoids extreme fluctuations in soil moisture can prevent problems.  Good soil drainage, mulching, and preventing root damage also help. Other soil factors may contribute to blossom end rot.  High soluble salts, low calcium and high cation (potassium, magnesium or ammonium) levels in the soil out-compete calcium on soil exchange sites, making it unavailable to the plant.

Having your garden soil tested at the beginning of the season can help monitor these soil issues. 

Cracking of fruit can be either radial or concentric.  In both types of cracking, cultivars vary considerably in their susceptibility.  Radial cracks form near the stem and may extend almost to the bottom tip of the fruit.  Tomatoes are more susceptible to this type of cracking as they ripen, particularly heirloom varieties.

Radial cracks are often the result of rain or excessive watering after a prolonged dry period.  Maintaining even soil moisture will help prevent cracks.  Concentric cracks form on the shoulders of the fruit, often appearing as rings of brown scar tissue.  A form of concentric cracking called weather checking, fruit russeting, or shoulder checking, results from water droplets on the fruit shoulder being exposed to full sun, often due to a lack of leafy cover and overhead irrigation.  Maintaining ample healthy foliage and keeping fruit dry can prevent shoulder checking.

Catfacing is a condition that distorts fruit growth at the blossom end.  The fruit develops deep, scar-like indentations that can extend the length of the fruit.  In catfacing, the female part of the flower develops abnormally due to low temperatures during flowering. Extended periods of cool daytime temperatures (60-65 degrees F) and cool nighttime temperatures (50-60 degrees F) can lead to catfacing.

High tunnels, row covers, or other protections that warm air temperatures can reduce damage during flowering if field conditions are cool.  Cultivars also vary considerably in their susceptibility to catfacing.

Zippering is characterized by the presence of brown tissue (resembling a zipper) running down the sides of tomatoes, often from the stem to blossom end. Zippering is the result of a flower anther remaining attached to newly forming fruit. Some theorize it is also associated with incomplete shedding of flower petals when fruit is forming. There is little that can be done to prevent zippering, except selecting varieties that are not prone to this disorder.

Sunscald occurs in fruit exposed to direct sun in hot weather.  Bleached and blistered areas develop on the exposed surface, eventually becoming dry and papery.  The best prevention is to maintain healthy foliage by protecting against defoliating diseases, avoiding excessive pruning, and using a closer plant spacing.

Puffiness results from poor pollination and leads to oddly-shaped fruit.  The locular gel (the liquid that surrounds the seeds) fails to fill the fruit’s inner cavity resulting in a fruit with flattened sides that lacks firmness.  Although eating quality is poor because of the lack of gel, some cultivars have been bred to be puffy so they can be stuffed more easily.

Ripening disorders

Several ripening disorders also affect tomatoes: blotchy ripening, yellow shoulder, and gray wall.  Tomatoes with blotchy ripening ripen unevenly with yellow or orange discolored areas on their surface or shoulders.  Yellow shoulder describes fruit discolored with green-yellow patches on the shoulders and may be accompanied by coarsely-textured fruit walls.  This disorder is usually caused by heat injury and insufficient potassium.

Tomatoes with gray wall have grayish-brown discolorations on the fruit wall and may also exhibit internal browning.  Gray wall typically appears on green fruit before ripening.  Factors that increase the severity of these disorders include cloudy weather, wet and cool conditions, high nitrogen, low potassium, and compacted soils.  Good irrigation management and organic soil and nutrient management will reduce the risk of these disorders. 

Another type of ripening disorder is caused by the Silverleaf whitefly (Bemisia argentifolii). Silverleaf whitefly larvae inject toxins into tomato fruit when feeding, leading to irregular ripening that can cause significant losses. Affected fruit will not ripen.

For more information on tomatoes log on to uky.edu/Ag/Horticulture/homeveggies.html or contact the Franklin County Extension Office by phone, 695-9035 or email DL_CES_Franklin@Email.Edu.UKy.

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