ANNUAL REPORT, 1946-47 63 



the various numbers of sprays were too small to be significant, the spraying defi- 

 nitely reduced the number of mummies. This work is being continued. 



In the experimental plantings there are a number of bushes infected with blue- 

 berry stunt, a virus disease. These are being kept to watch the progress of the 

 disease. As yet, there has been no evidence of any spread from diseased to 

 adjacent healtny bushes. However, the progress of the disease in an infected 

 bush is much more rapid than had been anticipated. So far diseased bushes have 

 been found in only two varieties, Cabot and Concord. Since the symptoms differ 

 in each variet}', buds from diseased bushes were set in healthy bushes of several 

 other varieties so that the symptoms might be studied as they developed. 



An infestation of a Lecanium scale had been slowly building up, particularly 

 on the variety Concord. Previous attempts to control it had been only partially 

 successful. In the spring of 1947 delayed dormant sprays of DDT emulsion, 

 D-542, and "Peninsula Oil" were applied in cooperation with the Entomology 

 Department. The DDT emulsion had little effect, "Peninsula Oil" killed most 

 of the scale, and D-542 eliminated them almost completely. 



Nutrition of the High-Bush Blueberry, Especially in Relation to Soil Reaction. 



(J. S. Bailey.) For many years it was believed that manure would kill cultivated 

 blueberry bushes. A comparison of horse, poultry, and cow manure over a 

 period of five years has shown that (1) the bushes will thrive where as much as 

 20 tons of horse manure per acre are applied, and (2) there is no significant dif- 

 ference among manures when they are used in such quantities as to give about 

 the same amount of nitrogen per acre. This phase of the work has been con- 

 cluded. 



In the summer of 1946, leaf symptoms of what appeared to be magnesium de- 

 ficiency were observed on a few blueberry plants. Chemical analyses of the 

 leaves of. several bushes revealed that they contained only 0.14 percent mag- 

 nesium or less. With the apple, 0.20 percent is considered the danger line. 

 When the analysis gets that low, an effort should be made to get more magnesium 

 into the tree. This situation in blueberries is being studied further. 



Magnesium Deficiency in Massachusetts Apple Orchards. (J. K. Shaw and 

 W. D. Weeks.) The leaf scorch typical of this deficiency has been little in evidence 

 during the past three years. This is not saying that magnesium deficiency is no 

 longer present. Probably it may interfere with best growth and fruitfulness and 

 still no serious leaf scorch be present. Moderate to heavy applications of Epsom 

 salts were applied to a large number of trees and leaf samples from 110 trees col- 

 lected for analysis. The analytical work is not yet completed, but so far there is 

 little indication of success in getting magnesium into these mature apple trees. 

 The recommended measures to alleviate magnesium deficiency are still 20 pounds 

 of Epsom salts in 100 gallons of the regular spray solution applied in three or 

 four of the earlier foliage sprays for immediate results, and dolomitic limestone, 

 1 to 2 tons per acre, for more lasting results. 



Thinning Apples with Sprays. (W. D. Weeks.) Because of a light bloom in 

 most of the Station orchards and injury to blossoms from spring frosts, extensive 

 trials to thin apples with sprays were not attempted in 1947. However, some 

 results were obtained with a commercial preparation of naphthalene acetic acid, 

 20 p. p.m. Early Mcintosh, Golden Delicious, Red Astrachan, Wealthy, and 

 Lobo were thinned quite effectively; while Kendall, Melba, Blackmack and 

 Richared were thinned excessively. Considerable dwarfing and distortion of the 



