70 MANUAL OF FRUIT DISEASES 
the return of dry air they are promptly carried to the apple. 
It is clear, then, that following a short rain it is but a question 
of a few hours before the fungus is actually inside the apple 
leaf. 
The relation of the development of G. Juniperi-mrginiane 
to the weather is very striking, and is a question of great im- 
portance as well as of great interest. From what has been said 
it is obvious that the weather factors concerned are moisture, 
temperature and wind. Moisture is necessary for sporidial 
production. Winds and warmth aid in evaporation and in 
sporidial liberation. Moisture again is necessary for germina- 
tion of sporidia, seciospores and teliospores. ‘Temperature is 
likewise a limiting factor in this connection. Winds appear 
to be the only agents of inoculation. It is not necessary that 
the winds be strong, since the spores are very light and float 
easily in air currents. 
Control. 
The simplest and most effective method of handling apple- 
rust consists in the eradication of the red cedars. This is 
practiced by larger growers where the disease has become 
important. This work must be done thoroughly. All red 
cedars within a radius of at least one mile about the apple 
orchard must be destroyed. The cost of this work has been 
found to be less than forty-eight cents an acre in West Virginia. 
It has been found that galls may produce teliospores and 
sporidia two months after the trees are cut. It is therefore 
advisable to burn any red cedars which are cut later than 
March first. The removal of galls from the red cedars is a 
commendable practice only when the cedars are more desired 
than the apples. Such may be the case in public parks and 
on private estates. The galls should be removed in advance of 
sporidial production, that is, before March first, to make sure 
of effectiveness. The work must be done every year. Spray- 
ing the cedars likewise is to be done only where the cedars are 
