384 AGRICULTURE OF MAINE. 



media. This fact is of great importance to the orchardist. 

 Dead limbs, piles of rubbish and rotted fruit which frequently 

 are allowed to accumulate in the orchard are breeding centers 

 for those fungi which attack the fruit, leaves, and wood of the 

 tree. Hence the first step in removing the cause of disease is 

 thorough orchard sanitation. 



t 



Non-parasitic Diseases. 



Winter Injury. Those parts of Europe and Asii. where the 

 apple is native have very moderate rainfall and are not subject 

 to such wide range and abrupt changes of temperature as in 

 this State. The northern limit of range of the apple except in 

 the case of the very hardy varieties is determined approximately 

 by the lowest winter temperatures, or — 30° to - — 32° F., re- 

 peated at frequent intervals. Some varieties, like the Baldwin 

 and Ben Davis, in Maine apparently are liable to be injured 

 where the repeated minimum winter temperatures are several 

 degrees warmer than this. 



Other conditions also enter into winter killing, such as defi- 

 cient rainfall in spring and early summer followed by a late 

 fall, thus preventing early growth, maturity and ripening of the 

 season's wood. Similarly too, late cultivation and the applica- 

 tion of large amounts of fertilizer rich in nitrogen may also 

 stimulate to late growth and prevent ripening of the wood before 

 cold weather comes on, and predispose to winter injury. The 

 amount of moisture which the plant cells contain at the time 

 the low temperatures are experienced is also a contributing fac- 

 tor. The more water they contain, beyond certain limits, the 

 more likely will they be injured by freezing. This probably 

 accounts for the fact that very frequently in Maine the trees in 

 the more exposed locations have suflFered less from winter-kill- 

 ing than those in more sheltered situations. There was better 

 drainage, the ground frozen more deeply and the roots chilled 

 and inactive and not supplying water to the plant tissues above. 



The severe winter-killing of 1906-7 was probably due to the 

 combined influence of low temperatures alternating with high 

 and a large percentage of water in the tissues of the trees. 

 Weather conditions of January, 1907, were particularly favor- 

 able to this as will be seen by examination of Fig. 56 which 

 shows within a week a record of — 40° F. and — 35° F. with 



