262 MANUAL OF FRUIT DISEASES 



SHELLING 

 Cause somewhat obscure 



Grape-growers in certain parts of America have known this 

 trouble for at least fifty years. It has been reported especially 

 from Connecticut, central and western New York, and 

 Michigan. What appears to be the same disease has been 

 observed in Australia (Queensland) and in many parts of 

 France. In France there appear to be two forms of shelling : 

 one in which there is a failure of the flowers to set fruit in some 

 or all parts of the cluster, known to the French as coulure ; the 

 second form, in which the fruits fall or shell. The latter type 

 is the more important in this country ; the losses at times being 

 serious. Fifty per cent of the fruit may drop when affected 

 with shelling, or rattling. 



Symptoms. 



Affected grapes fall two or three weeks before maturity. 

 Those diseased berries, particularly of the green varieties, 

 exhibit a peculiar though indistinct mottling of the surface. 

 The skin becomes abnormally thick, and the whole berry is 

 harder than healthy berries of the same age. The interior of 

 such a fruit shows a brown zone just beneath the skin. The 

 taste of shelling berries is noticeably insipid as compared to 

 the tart, astringent flavor of the healthy, unripe berries. Shel- 

 ling grapes separate easily from the stem, leaving the latter 

 as if cut with a knife; no such phenomenon occurs with un- 

 affected berries. Generally those berries at the lower end or 

 at the extremity of the shoulder are first to fall from the bunch. 

 Shelling is not always accompanied by foliage discolorations, 

 nor is a browning of the leaves a certain indication of the disease. 



Cause. 



The cause of grape-shelling is obscure, although a great 

 many suggested causes have been eliminated by close students 

 of the trouble. Among the excluded primary causal factors 



