APPLE DISEASES 33 



and is also unfavorable to bitter-pit. Most alert commercial 

 fruit growers practice thinning. It is an operation essential to 

 regularity of bearing. It makes yields regular and bitter-pit 

 is consequently reduced. Trees with a light crop and un- 

 usually large-sized fruit are most subject to pit. Again, over- 

 crowding favors the disease. Manuring has a bearing on the 

 development of stippen. The practice is commendable in that 

 it not only supplies food, but neutralizes toxic substances in 

 the soil. It also affects the moisture content of the soil and 

 thus transpiration is modified. The water-elimination process 

 in its relation to bitter-pit has been emphasized. Although 

 long years of experimentation are necessary to determine the 

 effect, if green-manuring were practiced in non-irrigated or- 

 chards the disease would probably be reduced. Cover-crops 

 are planted by many of the leading apple-growers. These 

 crops aid in regulating the water-supply of the apple, and 

 when plowed under will conserve the soil moisture. The ques- 

 tion of drainage should not be overlooked. This disposes of 

 excessive water during the days of heavy rainfall, and conserves 

 moisture during drought-periods. The disease is worst in 

 low, wet portions of an undrained orchard. Moderation should 

 be practiced in the matter of irrigation. The heavy applica- 

 tion of water following a drought-period is favorable to stippen 

 development. Excess should be avoided, and the aim should 

 be to maintain uniformity of moisture conditions. Thorough 

 orchard cultivation is advised. This operation affords proper 

 aeration of the soil and consequent normal and efficient root- 

 action. It conserves moisture during periods of dry weather, 

 and as a result transpiration is properly regulated. Spraying or 

 dusting operations have an important bearing on the problem ; 

 for, if neglected, the foliage is almost sure to be diseased and 

 therefore less efficient both in the manufacture of food and in 

 transpiration. It has been found that diseased leaves trans- 

 pire less than healthy ones. 



