582 ANNUAL REPORT OF THE Off. Doc. 



I have tried to enlarge my limited observations for the past season 

 by seeking information from apple groAvers in the four states nam- 

 ed. The majority of these reports show that red cedars have grown 

 very near badly infected orchards and there is abundant and strik- 

 ing circumstantial evidence of their relation to outbreaks. Some- 

 times the cedar trees are reported at a distance of ^ to 1 mile. This 

 is no bar to their being a source of infection. Estimates indicate 

 that a "cedar apple" is capable of producing upwards of 30,000,000 

 infection spores; this would furnish 50 for every square foot of 

 a 20-foot fence encircling the tree at a distance of one mile from 

 it; and ordinarily an infected cedar tree produces quite a number 

 of cedar apples. Of course the chances are against most of the 

 infection spores being carried as far as a mile; but certainly many 

 are carried farther by strong winds. The vast majority will chance 

 not to lodge upon a proper host, and of those that do, many will 

 perish in the absence of favorable conditions for germination. But 

 there are enough infection spores formed to insure a certain number 

 finally meeting with conditions suitable for growth. 



More anomalous are cases of apples near cedars rusting less than 

 those farther away. Three conditions might bring this about. The 

 varieties growing nearer the cedars might be non-susceptible ones; 

 winds prevailing at the proper time for transferring spores might 

 carry them away from the nearer trees, and towards trees further 

 away in another direction; and thirdly, the cedar trees that were 

 in mind may not be infected with any of the three dangerous species 

 of rust, while some unnoticed cedar nearer the infected apples 

 might be the real source of the rust. For the rust species, although 

 common, do not necessarily infest every cedar tree. In our class 

 work in freshman botany, we have occasion to use a good many 

 cedar apples annually, and we go to three or four lots of cedar 

 trees where they may be had in greatest abundance; all of these 

 have susceptible pomaceous plants growing near. 



Two or three correspondents do not know of any cedar trees in 

 their localities, and yet have the rust. If there is no confusion of 

 other apple troubles with the rust, the question arises whether after 

 all a close search might not reveal a few cedar trees that have passed 

 unnoticed. 



While some striking cases have been reported of prevailing spring 

 winds carrying infection from cedars to apple, it must be remember- 

 ed that an occasional blow from an unusual quarter, if at just the 

 right time, may be more potent than days of wind when conditions 

 are not suitable for infection. The question of how far spores may 

 be carried in quantity, is the question of how far any dust-like 

 particles may be carried, and depends upon the force of the wind, 

 its upward or downward path, and the encountering of obstacles. 

 A mile or two seems not at all impossible. 



Kemoval of cedar trees near apple orchards has frequently given 

 highly satisfactory results. The efficiency of this measure will be 

 greatest when the cedars removed are the sole or main source of 

 infection for this particular orchard. Wherever valuable though sus- 

 ceptible varieties of apples grow, cedar trees should be removed 

 from the vicinity as completely as is practicable. Wild pomaceous 

 plants, susceptible like the apple, may grow among the cedars and 



