Jan. ax, is»i8 Irrigation Experiments ou AppleSpot Diseascs 133 



affected tissue, but with negative results. Close observations have been 

 made on the work of insects in orchards where the disease was serious, 

 but no evidence has been secured to indicate the association of any insect 

 with the production of the disease. Orchards affected with rosette are 

 sometimes also affected with cork, but the latter disease occurs in orchards 

 that are free from the former. In nearly every case where the disease has 

 been observed either in the East or West, its occurrence in the orchard 

 has been closely correlated with certain peculiar soil conditions; some- 

 times an excess of alkali or an outcropping of slate, but more often a 

 shallowness or openness of the soil. In most sections cork has been most 

 serious when there was a shortage in soil-water supply, either resulting 

 from light rainfall or a lack of irrigation. 



An orchard at Entiat, Wash., that has been seriously affected with 

 cork has been under close observation for the past three years. The 

 orchard is located on a low bench near the Columbia River, and has had 

 a permanent cover crop of alfalfa. Soil samples from the orchard showed 

 that in the sections where spotting had been most prevalent the surface 

 soil was only about 3 inches deep and was composed of a coarse sand 

 with only a small percentage of humus. The subsoil, which was more 

 than 6 feet deep, differed from the surface soil only in the absence of the 

 humus and was underlain with coarse gravel. In sections of the orchard 

 where spotting had been less prevalent, the soil was found to be a much 

 finer sand, and in sections where no spotting had occurred it was a typical 

 volcanic ash, very fine in texture, closely compacted when wet, and very 

 retentive of moisture. Soil-moisture determinations made soon after 

 the spring rains showed that while the surface soils in the different orchard 

 sections retained their moisture fairly well, the subsoil in the first section 

 dried out quickly and that in the last section was very retentive of its 

 moisture. It will be seen that the occurrence of the disease varied with 

 the character of the soil, particularly with the water-holding capacity of 

 the subsoil. 



The irrigation of the orchard was inadequate. The furrows were 5 

 feet from the tree rows, and alfalfa growing near the trees and in the tree 

 rows was yellow, frequently wilted, and very evidently suffering from 

 lack of water. The trees suffered from drouth, especially in the spring, 

 before the irrigations were begun. In 191 6 the first irrigation was made 

 several weeks later than usual and the trees became very dry. Later 

 the apples developed an unusually high percentage of cork, the disease 

 first appearing in blister form soon after the petals had fallen. The con- 

 ditions in the orchard indicated that the soil-water supply was at least 

 one important factor in determining the amount of disease. 



The circumstances under which cork and drouthspot have occurred 

 in the Champlain Valley have been quite fully described by Mix {14). 



A special form of cork known in certain sections as "Yorkspot" and 

 in others as "hollow-apple" has been found particularly common on 



