130 Journal of Agricultural Research voi. xii. no. 3 



OTHER PHYSIOLOGICAL SPOT DISEASES OF THE APPLE 

 DROUTHSPOT 



The term "drouthspot" (2) has been applied to certain fairly large 

 areas of dead brown tissue usually occurring near the surface of the apple, 

 but sometimes found deeper in the flesh. The disease may appear 

 at almost any stage in the development of the apple, but the fruit 

 appears to be more susceptible after it is one-third grown. The spots 

 are usually located on the blossom half of the fruit. In typical cases 

 the trouble first appears as large, irregular, water-soaked spots that 

 often have a reddish margin and are usually covered with drops of a 

 yellowish, sticky ooze that is sweetish to the taste, and later hardens 

 into a brittle, crystalline-like deposit (PI. 3, D). At this stage the spots 

 resemble fireblight infection (caused by Bacillus amylovorus) and are 

 sometimes mistaken for it. Upon cutting the apple open a very shal- 

 low layer of dead brown tissue is found in the region of the vascular 

 network just beneath the skin. Occasionally brown streaks follow the 

 vascular bundles deeper into the apple pulp. The afifected tissue is 

 very bitter to the taste. The skin of the apple over the diseased area 

 finally regains its normal appearance; but growth is arrested at this 

 point, and the enlargement of the surrounding tissue soon gives rise 

 to a much misshapen apple (PI. 3, E, F). On account of its manner 

 of development, the disease has sometimes been referred to as "spot- 

 necrosis" {13). Mix {14) has given a full discussion of the characters 

 of the disease as it occurred in the Champlain Valley of New York. 



The above description applies particularly to the trouble as it has 

 been observed on Winesap and Stayman Winesap apples in the irrigated 

 sections of the West. It was first produced experimentally at Wenatchee, 

 Wash., in 191 3, by subjecting Winesap trees to a sudden and severe 

 drouth when the fruit was about i inch in diameter. At about the 

 same time it was observed at Peshastin, Wash., on Ben Davis trees that 

 had suffered from a similar drouth. It occurred again at Wenatchee in 

 1 91 4 and in 191 5, always on trees that had been subjected to a sudden 

 and severe drouth and that had been making a normal or vigorous 

 growth earlier in the season. The drouth periods resulted from trouble 

 with the irrigation canals. The affected trees were usually located on 

 shallow soils or on soils underlain with coarse gravel at a slight depth, 

 thus making them peculiarly susceptible to drouth. 



In 1 91 5 a series of drouth periods occurred, the first and most severe 

 coming the latter part of June and the first of July, the second the latter 

 part of July, and the third about the middle of August. At the time of 

 the first drouth even the trees on deep soil began to suffer, and those on 

 shallow soil lost a large percentage of both their foliage and fruit. The 

 fruit that remained on the trees was much shrunken in size, sometimes 

 being reduced to two-thirds its normal diameter. White Pearmain ap- 



