PROBLEMS OF PLANT PATHOLOGY 











F. L. Stevens 



Plant pathology is primarily and essentially an economic 

 subject, and it is mainly from this viewpoint that it will be con- 

 sidered in this paper, attention being called also to the relation 

 which the practice of pathology bears to science. The chief 

 application of plant pathology is to agriculture, and as so applied 

 the main, practical achievements may be summarized briefly as 

 follows: (i) the control or partial control of various fungi, notably 

 of orchard, vineyard, truck, and floral crops by sprays of copper 

 compounds; (2) the substitution in many instances, notably on 

 drupaceous hosts, of lime-sulphur compounds; (3) treatment by 

 excision and the introduction of so-called tree-surgery; (4) the 

 avoidance of susceptible varieties, for example, carnations, pears, 

 strawberries, chrysanthemums, cowpeas, asparagus, and can- 

 taloupes; (5) the development or utilization of disease-resistant 

 or partially resistant strains, for example, asparagus, pears, water- 

 melons, cowpeas, oats, wheat, flax, and cabbage; (6) the prevention 

 of disease through knowledge of necessary alternate hosts, for 

 example, pomaceous rusts; (7) the prevention of disease intro- 

 duction by quarantine and inspection; (8) prevention through 

 knowledge of mode or time of infection, or mode of transference, 

 for example, certain cereal smuts, bean and cotton anthracnose, 

 cabbage blackrot, and potato scab. 



In this enumeration, the first 5 captions cover the major part 

 of the early fruits of pathology, the easily gathered fruits, first 

 ripe, and which could be harvested without deep, scientific knowl- 

 edge. Such practices do not necessarily rest upon subtle principles, 

 but are rather the outcome of cut-and-try methods of experience. 



The accident which led to the experiments which in turn 

 brought into prominence the use of copper sprays and thence led 

 to much that has been done to perfect sprays and dust applications 



'Paper presented at the Botanical Conference held in connection with the 

 Quarter-Centennial Celebration of the University of Chicago, June 1916. 



297] (Botanical Gazette, vol. 63 



