34 ■ MISC. PUBLICATION 16 8, U.S. DEPT. OF AGEICULTURE 



months have been found to favor the disease. Fruit from the in- 

 terior shaded portions of the tree is more susceptible than that from 

 the exposed portions, and fruit from trees bearing a light crop is 

 more susceptible than fruit from trees bearing a heavy crop. (<§, 22^ 



mo, im, 126, 127, 111, 239.) 



JONATHAN SPOT 



Jonathan spot occurs on apples grown in all parts of the United 

 States and is also loiown to occur in other parts of the world. The 

 variety most commonly affected and on which the disease was first 

 described is Jonathan; other varieties showing spots so similar they 

 are generally classed as Jonathan spot are Esopus Spitzenburg, 

 Wealthy, Yellow Newtown, Grimes Golden, Gravenstein, Ortley, Ar- 

 kansas Black, Twenty Ounce, and Wolf River. 



The spotting is apparently not caused by either fungi or bacteria. 

 It is common after a dry season and in some years is more common 

 on large apples than on small ones. It is occasionally found on ripe 

 apples before picking, but is most prevalent on apples in transit or 

 storage, especially if temperature and humidity are high and ventila- 

 tion is poor. 



Jonathan spots appear in the early stages as brown, roughly cir- 

 cular areas one sixteenth to one eighth of an inch in diameter which 

 are abruptly but only very slightly sunken; in later stages they 

 become somewhat more sunken and show as irregular lobed areas 

 sometimes a quarter of an inch across (pi. 5, A). In early stages the 

 spots are confined to the color-bearing cells of the skin, but under- 

 lying tissues become affected as ih^j dry out after the skin is killed. 

 These spots sometimes become infected with Alternaria or other rot 

 fungi, and when this happens they wdll be found to overlie a brown 

 spot that extends into the flesh for an eighth of an inch or more. 

 Naturally, the depth of such spots depends on how long the fruit is 

 exposed to conditions that favor decay. 



The disease is of importance chiefly because of its effect on the 

 appearance of the fruit, although it is sometimes followed by decay, 

 as mentioned above. Its most serious characteristic is a tendency to 

 develop in transit or storage to such an extent that marked damage 

 results to fruit that was apparently in good condition when shipped 

 or stored. 



Brown spots that resemble Jonathan spot are sometimes seen on 

 Rome Beauty apples. These, however, seem to occur only at lenti- 

 cels ; they have a blurred indefinite edge, and are rarely sunken, even 

 as slightly as typical spots on the Jonathan variety. Nothing is 

 known of their relation to orchard or storage conditions except that 

 they do not usually develop until late in the storage season. In the 

 absence of evidence to the contrary, it seems best to consider them a 

 form of Jonathan spot. 



The most effective method of controlling Jonathan spot is to move 

 the apples promptly into cold storage, avoiding delavs at warm 

 temperatures. {18, 22, 26, 62, 80, 100, lU, 168, 176, 179, 180, 186, 217.) 



KING DAVID SPOT 



King David spot occurs on apples of the King David variety. The 

 spots appear as black or dark-greenish areas up to about one fourth 



