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COMMON TOMATO FRUIT DISORDERS

Steve Reiners

Associate Professor in Horticultural Sciences

(see below)

Blossom-End Rot (BER) - Characterized by a large, leathery brown or black spot on the bottom of the fruit. In some cases. internal BER can occur within fruit. BER is caused by a lack of calcium in the fruit which causes the fruit to die back creating the characteristic spot. What can you do to prevent it? Have your soil tested to make sure calcium is present in adequate amounts. Chances are the calcium level will be fine but if it is not, add limestone (for acid soils with a pH below 6), or gypsum when the soil pH is in the 6 to 7 range. If calcium levels are okay, the next most important control is to maintain optimum soil moisture. When tomatoes experience the slightest bit of drought, BER may result. Using mulches will usually significantly decrease BER as excessive evaporation from soil is reduced. Varieties will vary in their susceptibility so if you have a problem with a particular variety, choose a new one next year. When sidedressing plants, using a nitrate type fertilizer like calcium nitrate is preferable to ammonium based ones like urea. Finally, don't bother to use calcium sprays. They are worthless in combating the problem.

Internal Browning (IB), Graywall (GW) or Blotchy Ripening (BR) - A complex of disorders that result in irregular ripening, yellowing or browning of fruit. Tobacco mosaic virus (TMV) has been implicated in some cases of IB but conditions can develop with out TMV being present. Symptoms often develop in the interior of dense plants with lots of foliage. Cloudy, wet and cool conditions, high nitrogen, low potassium and compacted soils will increase the severity.

Catface - Seen as severe scarring on the blossom end of the fruit, usually more severe on the first fruit harvested in the summer and on very large fruited varieties. Extended periods with temperatures 60-65F during the day and 50-60F at night cause the problem. The temperatures do not directly affect the fruit but instead the flowers when they are very small. Protection of some kind (row covers, wall of waters, hot caps, etc.) will minimize the problem as will changing varieties. Although we normally think of the early fruit being affected, cool nights over the next few weeks could cause the problem in later plantings.

Fruit Cracking - This is due to rapid uptake of water by the fruit, as a result of heavy rain or heavy watering. The water can move to the fruit through the roots and also directly into the fruit around the stem scar. Cracks may be concentric (around the stem), or radial (radiating out from the stem). To overcome the problem, choose crack resistant varieties like Mountain Pride or Mountain Delight and maintain uniform soil moisture by mulching and steady watering.

Fruit Russeting — Also known as weather checking is due to the presence of water (irrigation, rain, dew) on the surface of the fruit for extended periods. Cool mornings later in the summer are ideal conditions for russeting to develop. Good air circulation around plants by growing on trellises can help.

Yellow Shoulders - The tops of the fruit never ripen completely, especially on fruit that are exposed to direct sunlight. The area under the yellow shoulders will be corky as well as discolored. This is partly a genetic problem that can be lessened by growing plants with the uniform ripening gene. Maintaining good foliage cover so fruit are shaded will also help. Remember, tomatoes do not need direct sunlight on the fruit to ripen!

Sunscald - Symptoms appear as a yellowish to white water soaked area on the side of the fruit exposed to the sun. It is more severe on fruit that have been heavily shaded and then suddenly exposed to the direct rays of the sun. Secondary bacterial or fungal infections can invade the sunscald area. To avoid this problem, ensure your plants are adequately fertilized so healthy foliage shades fruit. Also, don't prune plants later in the season after fruit have formed.

Stink Bug Feeding — Pale, yellow, cloudy spots on the fruit surface with shallow, corky areas in the flesh are caused by stink bug feeding. Stink bugs range in size from 3’8 to 5/8 inches in size and are brown or green in color. Control bugs to minimize the problem.

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