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Common Tomato Fruit Disorders

Thomas A. Zitter, Professor, Department of Plant Pathology, Cornell University, Ithaca, NY,
and
Steve Reiners, Associate Professor, Horticultural Sciences, NYSAES, Geneva, NY

(Reissued May, 2004)

Blossom-End Rot (BER) - Characterized by a large, leathery brown or black spot on the bottom of the fruit. (Fig. 1). In some cases, internal BER can occur within fruit. It generally occurs on the first fruit cluster. 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. If growing on bare ground, avoid cultivating too close to plants to prevent root damage and the need to maintain deep root development. Varieties will vary in their susceptibility so if you have a problem with a particular variety, choose a new one next year. When side-dressing 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. The same problem can occur on pepper and eggplant.

Fig. 1 Blossom-end rot Fig. 2 Graywall, external symptoms Fig. 3 Graywall, internal Fig. 4 Blotchy ripening

Internal Browning (IB), Graywall (GW) or Blotchy Ripening (BR) - A complex of disorders, hence the various common names applied, that result in irregular ripening, yellowing or internal browning of fruit. Tobacco or tomato mosaic viruses (TobMV, TomMV) have been implicated in some cases of GW, but plants free of virus and those resistant to virus also develop GW. GW typically develops on green fruit prior to harvest. It appears as black to dark brown necrotic tissue in the walls of the fruit. (Fig. 2). The outer walls are most frequently affected as seen when fruit are cut. (Fig. 3). Blotchy ripening. (Fig. 4). gets its name because the fruit ripens unevenly, with the patches that don't ripen or do so after the rest of the fruit is over-ripe. 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. (Fig. 5). Extended periods with temperatures of 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 extended over the mid-season 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). (Fig. 6 a, b) , or radial (radiating out from the stem). (Fig. 7). To overcome the problem, choose crack resistant varieties like Mountain Pride or Mountain Delight and maintain uniform soil moisture by mulching and steady watering.

Fig. 5 Catface on variety Celebrity Fig. 6a Concentric crack Fig. 6b Concentric crack Fig. 7 Radial cracking

Fruit Russeting or Shoulder Checking - Also known as weather checking, this malady is due to the presence of water (irrigation, rain, dew) on the surface of the fruit for extended periods. (Figs. 8, and 9). Cool mornings later in the summer are ideal conditions for russeting to develop. Good air circulation around plants by growing on trellises can help.

Figs. 8 and 9. Fruit russeting (skin checking or weather checkin) on Count II Fig. 10 Zippering

Zippering - A thin longitudinal scar extends from the stem scar to the blossom end. (Fig. 10). The longitudinal scar has a series of transverse scars which resemble a zipper. Sometimes a hole opens to the locule as shown in this picture. This defect happens when the flower anthers fuse to the ovary wall of developing fruit and occurs most commonly when fruit set takes place in cool weather. Varieties can vary in their susceptibility to this malady.

Yellow Shoulders - The tops of the fruit never ripen completely, especially on fruit that are exposed to direct sunlight. (Fig. 11). 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!.

Fig. 11. Yellow shoulders Fig. 12. Sunscald Fig. 13. Excessive heat in the greenhouse or high tunnel

Sunscald. and Excessive Heat - Symptoms appear as a yellowish to white water soaked area on the side of the fruit exposed to the sun. (Fig. 12). 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. Excessive heating can buildup dramatically in greenhouses and high tunnels on sunny days, particularly if no ventilation is provided. This can lead to direct death of young tissues on the fruit surface and may extend deeply into the fruit wall. (Fig. 13).

Stink Bug and Tarnish Plant Bug Feeding - Pale, yellow, cloudy spots on the fruit surface with shallow, white pithy areas in the flesh are caused by stink bug feeding. Stink bugs range in size from 3/8 to 5/8 inches (mean ½ inch), and are brown or green in color. (Fig. 14). Such feeding will result in tomatoes showing cloudy spot. (Fig. 15). Adult tarnished plant bugs are about ¼ inch long and are brown, tan or greenish with darker markings on their wings and back. TPB will feed on newly formed fruits that are succulent, and secrete a toxic substance from their salivary glands which kills the cells surrounding the feeding sites. (Fig. 16). As the fruit enlarges, healthy tissue will expand while the dead tissue does not, which results in distorted and malformed fruit. Such fruit may also be invaded by common fungi such as Alternaria alternate. (Fig. 17). Alfalfa is a preferred host, and when alfalfa is harvested, this stimulates lygus migrations into tomatoes that are unprotected when the sides of high tunnels are raised. Control bugs to minimize the problem.

Fig.14. Stink bug leading to Fig. 15. Cloudy spot Fig. 16. Tarnish plant bug injury leading to Fig. 17. Alternaria alternata.

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