A number of different varieties of apples commonly show this peculiar spotting of the fruit. The Jonathan, Esopus, Wealthy, Ortley, Wolf River and some other varieties are severely affected; the disease has been noted on several other kinds, including the Nero, Smokehouse, Newtown Pippin, Yellow Newtown, Grimes, Arkansas Black, Peter, Hibernal and Patten. The common occurrence of this disease on the Jonathan has given rise to the name Jonathan spot. In Minnesota the growers call what appears to be this disease the Wealthy spot. Apple orchardists generally hold to the opinion that thin - skinned varieties are most susceptible.
There is no evidence that the Jonathan spot occurs outside of the United States. Attention was called to the disease in Virginia and West Virginia in 1911. It has been under observation in New Jersey since 1912; in that state it is a very troublesome storage disease. The growers of the Jonathan and Esopus varieties in Washington and Oregon have been the heaviest losers on account of this Fruit Spot. It develops both in storage and en route to eastern markets. Fruits leaving the Pacific Coast in good condition may show objectionable spotting when placed on sale in the East. This peculiarity of the disease has impaired the commercial standing of the Jonathan to no small degree.
The spots may appear while the fruit is still on the tree, or after it has been picked. In the latter case they may develop in transportation or in storage. The spots are frequently in great abundance. A characteristic lesion may be described as follows: rarely more than one-eighth to three-fourths of an inch in diameter, it is circular in shape; the color is light-brown at first and with some varieties it remains so for a long time, in consequence of which the spot is inconspicuous. On red varieties the color darkens very early in the development of the lesion. The surface of the affected area is abruptly but slightly depressed. The affected tissue is dry and often only the skin appears to be discolored. In contrast to other Fruit Spots it is more superficial than bitter pit, New England Fruit Spot, and young Bitter Rot lesions.
The cause of Jonathan spot is not certainly known. Several theories and opinions are held in explanation of the causal nature. Some believe that the disease is non-parasitic; others are of the opinion that a species of fungus, an Alternaria, is responsible; and still others champion the opinion that gas causes the trouble. It may be safely stated that none of these ideas and theories are based on conclusive proof. It is very possible that two kinds of spots may occur together on the same fruit; one of which is non-parasitic in nature, and the other caused by some fungus, possibly the one already mentioned. Furthermore, gases such as formaldehyde, sulfur and ammonia may produce spots which are at present indistinguishable from those of fungous or non-parasitic origin. Ammonia from the cooling apparatus has been suggested as a causal factor. It has been acceptably demonstrated that arsenate of lead is not the cause of the Jonathan spot. Spots are found on unsprayed as well as on sprayed fruits. While the cause is yet somewhat obscure it is known that the spotting is more common subsequent to a dry season. The disease was severe following the dry summers of 1910, 1911 and 1914; while after the relatively wet season of 1912 it was less serious. In storage the disease is found most commonly where the fruit is kept in ordinary storage for some time before being placed in cold storage. It also is favored by poor storage ventilation and by improper storage,temperatures. Where a relatively high temperature prevails, spots develop abundantly. Under such conditions the fruit often "sweats" and rapidly respires. Apparently the causal factor comes from an external source and gains entrance through the lenticels and through other small fruit cracks as evidenced by the fact that such points serve as centers of all lesions. Since investigators are not generally agreed as to the causal agent, and since the possibility that two or more diseases are confused under the same name, the cause of Jonathan spot remains to be further investigated.
Fruits which hang on the tree too long show the disease more commonly than in cases where they are harvested at the proper time. Fruits picked at maturity, rushed to storage, and consumed within a few days after removal from cold storage will not develop the disease to any serious extent. Susceptible varieties like the Jonathan are likely to be severely spotted if the apples are withheld from cold storage, or are merely placed in common storage. It has been estimated that the trouble is quadrupled under conditions of cellar storage as opposed to the amount developed in cold storage. In cold storage the spots which do appear are smaller and less conspicuous. It is to be noted, of course, that the cold storage should be properly ventilated and the temperature should be standard (32° Fahr.).
Scott, W. M., and Roberts, J. W. The Jonathan Fruit Spot. U. S.
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1915. Swingle, D. B. Fruit diseases in Montana. Jonathan spot. Montana Agr. Exp. Sta. Circ. 37: 314. 1914. Norton, J. B. S. Jonathan fruit spot. Phytopath. 3: 99-100. 1913. Cook, M. T., and Martin, G. W. Jonathan spot rot. New Jersey Agr. Exp. Sta. Rept. 1914: 500 - 503. 1915. Cook, M. T., and Martin, G. W. The Jonathan spot rot. Phytopath.
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4:102 - 105. 1914. Stakman, E. C, and Rose, R. C. A fruit spot of the wealthy apple.
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