| Apple -- Fruit Russeting | |||
| Cause:
There are many resons for fruit to russet including cool, wet weather, frost, pesticides, viruses, fungi and bacteria. Golden apples are more susceptible to russeting than red apples. Each cultivar is affected differently by the above factors. The d’Anjou pear is also susceptible to fruit russeting. Russet results from the damage to epidermal cells that occurs within the first 30 to 40 days after petal fall. Once damaged, a brown layer of suberized cells form in the lower epidermal region. As cork cells develop in this area, they push outward and become exposed to the surface as the fruit matures.
Cool (not necessarily freezing) weather and wet fruit, especially from pink-blossom stage until 3 weeks after petal fall can cause russeting. 'Golden Delicious' is most susceptible to russeting. This kind of weather may be the cause or may only encourage growth of the fungi and bacteria discussed below. Many spray materials (including surfactants), especially emulsifiable concentrates and materials containing copper, zinc, or calcium, if not evenly distributed by spray equipment can produce a russet on apples. Several fungi including powdery mildew, Aureobasidium pullulans and Rhodotorula glutinis can russet fruit also. Cultivars such as 'Jonathan' and 'McIntosh' that are susceptible to powdery mildew therefore are affected by this type of russeting. The latter two fungi are common on the surface of apple fruit and leaves. Fruit are susceptible to this king of russet during bloom and at least 4 weeks after petal fall. A study in Hood River found that these later 2 fungi were not major factors contributing to russet of d’Anjou pear fruit. Several different kinds of bacteria including Erwinia herbicola and Pseudomonas sp. that produce high levels of the plant hormone indole-3-acetic acid (IAA). These bacteria have been shown to increase russeting when inoculated onto pear fruit. Fuji apples have a newly described but unknown cause of russeting, which has been called flecking. Severity increases during alternate years. |
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| Symptoms:
Russeting caused by cool weather and wet fruit often is associated with corky lenticels and tan markings shaped like rain-splashed water droplets. These markings are more abundant at the stem end.
Frost russeting usually is characterized by a band that forms either partially or completely around the fruit. Russeting from spray materials is likely to be found where spray droplets accumulate, such as the lowest portions of the fruit. Russeting from powdery mildew is tan to gray and has a netted appearance. |
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| Cultural
control:
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| Chemical
control: Using these products to control scab during bloom also aids russet control.
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| Biological control: Use of BlightBan A506 for control of fire blight may help reduce rusetting on pears due to IAA producing bacteria. It contains Pseudomonas fluorescens strain A506 which does not produce IAA. 12-hr reentry. | |||
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References: Matteson-Heidenreich, M.C., E.A. Corral-Garcia, E.A. Momol, and T.J. Burr. 1997. Russet of apple fruit caused by Aureobasidium pullulans and Rhodotorula glutinis. Plant Disease 81:337-342. Lindow, S.E., et al. 1998. Occurrence of indole-3-acetic acid-producing bacteria on pear trees and their association with fruit russet. Phytopathology. 88:1149-1157. |
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| Content edited by: Jay W. Pscheidt on January 1, 2009 | |||
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