MAEKET DISEASES OF APPLES, PEAKS, QUINCES 5 



AMMONIA INJURY 



(See Pears, Ammonia Injury, p. 49 and pi. 12, F.) 

 APPLE-CEDAR RUST 



(Gymnosporanffium jufiiperi-virgifiian<w Schw.) 



Apple-cedar rust occurs in practically all apple-growing sections 

 of the central and eastern United States. It is found onlj^ rarely on 

 the market, and even then merely as a slight blemish, since badly 

 marked fruit is usually culled out before shipment. The varieties 

 most often affected are York Imperial, Wealthy, Jonathan, Ben 

 Davis, and Kome Beauty. The rust fungus belongs to a large group 

 of fungi that must complete different stages of their life on different 

 hosts. The second or alternate host of apple-cedar rust is redcedar, 

 on which the fungus produces the familiar rough, brownish galls 

 known as cedar apples. From these it spreads in the spring to 

 apple leaves and young fruits, but it must pass again to the cedar 

 if it is to continue its development. 



Infection with the rust fungus takes place when the fruit is 

 young. Its result is either to cause the fruits to drop while still 

 undeveloped or so to stunt their development that they fail to reach 

 the average or normal size for the variety and often become notice- 

 ably flattened or otherwise malformed. 



Bust usually appears on the calyx end of the apple as grayish- 

 yellow to yellow areas that yslvj in superficial diameter from about 

 one eighth to three fourths of an inch and extend into the flesh for 

 a fourth to half an inch, or even to the core (pi. 4, D, E). The sur- 

 face of the spots may be smooth, or it may be roughened with the 

 spore-producing bodies of the fungus (aecia), these being in the 

 form either of pimples or of open cup-shape'd receptacles with flar- 

 ing papery edges. None of these will measure over a sixteenth of 

 an inch in diameter. The flesh beneath rust spots is woody and 

 usually greenish in color, though in the AVinesap and the Ben Davis 

 the green is sometimes intermixed with a pronounced browning. 



The disease can be controlled by removing all cedars in the neigh- 

 borhood of an orchard; in practice it has been found necessary to 

 extended the eradication to a distance of li/> to 2 miles, (i^, 25, 81^ 

 82, 100, lU, 122, 168, 160, 183, 195, 208, 209, 219, 223, 226, 229, 230.) 



Quince rust {Gymnosporangimn- glohosum Farl.) sometimes at- 

 tacks apples, producing dwarfing and distortion and an internal con- 

 dition like that shown in plate 4, F, which affects more of the fruit 

 tissue than that caused by apple-cedar rust. Aecia are not usually 

 produced. 



APPLE-MAGGOT INJURY 



{Rliagoletis pomonella Walsh) 



OCCURRENCE, SYMPTOMS, AND EFFECTS 



The injury caused by the apple maggot, which is often found in 

 apples from the northeastern part of the United States, consists of 

 small tunnels winding through the flesh of the apple, although there 

 may be little or no external evidence of infestation (pi. 20, A). 



