MARKET DISEASES OF FRUITS AND VEGETABLES 29 



Northwestern Greening, Rhode Island Greening, Golden Delicious, 

 and Delicious are less commonly affected. 



In the Shenandoah-Potomac valley districts, orchards of Ben 

 Davis, Gano, and Oldenburg are most frequently affected. Yellow 

 Transparent, Jonathan, Rome Beauty, and Grimes Golden have 

 also been found affected in these districts (34). 



In the Pacific Northwest cork has been observed on most 

 varieties. It is probably most serious on Yellow Newtown, Rome 

 Beauty, Jonathan, and Winesap. The Delicious variety may in 

 some cases benefit from boron fertilization even though none of 

 the usual deficiency symptoms are evident. It has been found 

 that where boron is lacking the fruit does not attain its character- 

 istic shape. The apples are inclined to be flat, with little tendency 

 toward prominent lobing at the calyx end (8). 



Apples affected with cork usually ripen a week or two earlier 

 than normal fruits, and their color is dull. When stored they 

 may develop characteristic symptoms of internal break-down like 

 fruit that is overripe when stored. 



Cork is a symptom of boron deficiency in the tree and occurs 

 when the boron supply in the soil is inadequate. There is some 

 evidence that extended drought increases the symptoms, probably 

 by preventing the tree from obtaining sufficient boron for normal 

 development of the fruit. It has been found that root injury 

 resulting from disking or waterlogging of the soil increases boron- 

 deficiency symptoms. 



Control of the disease depends on application of boron in the 

 form of boric acid or borax to the soil or by spraying the trees, 

 when in leaf, with a weak solution of either of these chemicals. 



(See 3, 4, S, 18, 19, 34, 40, 49, 78, 82, 84, 137, 142.) 



Drought Spot 



The name "drought spot" came into use in 1916 when Mix (89) 

 described it along with cork, a disease that had been known for 

 many years. The two diseases were considered to have similar 

 causes. Cork is now generally ascribed to a lack of boron. Boron 

 deficiency is also regarded as the cause or one of the principal 

 causes of certain other symptoms previously identified as drought 

 spot or heat injury. Now that some of the underlying causes of 

 these disorders are better known, and since there appears to be 

 no accurate description of drought spot that sets it apart from 

 cork and heat injury it seems best to discontinue the use of the 

 name. (See Cork (Boron-Deficiency Cork), p. 27, and Heat In- 

 jury, p. 37.) 



(See 13, 84, 89.) 



Fisheye Rot 



(Corticium centrifugum (Lev.) Bres.) 



Fisheye rot occurs on apples grown in the Pacific Northwest 

 including British Columbia and also on those grown in eastern 

 United States. In western apples it is difficult to distinguish from 

 bull's-eye rot. The spots may be only specks or up to 1 inch in 

 diameter, but most of them are less than 1 inch unless several 

 coalesce. The surface of a spot is usually brown and the center 

 pale, but a spot may be cream-colored or uniformly brown. The 



