PHYCOMYCETES 171 



comparatively resistant sorts. Soon after the discovery of Bordeaux 

 mixture, and more than thirty years ago, this fungicide was effect- 

 ively used as a preventive of the late blight. By repeated experi- 

 ments under a variety of conditions it has now been abundantly 

 shown that the proper use of Bordeaux mixture will, in ordinary 

 seasons, hold this disease in check, reducing its ravages to a small 

 minimum (compare Fig. 63). It is ordinarily advisable to begin 

 spraying with 5-5-50 Bordeaux when the plants are about six 

 inches high, and at least three thorough applications from ten days 

 to two weeks apart are advised. In some cases two additional 

 applications may be necessary. Again, it should be remembered 

 that the fungus is carried over winter largely, or perhaps entirely, 

 by a hibernating mycelium in the tubers, and that every effort 

 should be used to secure seed potatoes from a field in which no 

 blight or rot has occurred. If this latter could be done in connec- 

 tion with a system of rotation, there is no apparent reason why 

 the disease might not be practically stamped out in any con- 

 siderable region. 



XX. DOWNY MILDEW OF LIMA BEANS 

 Phytophthora Phaseoli Thaxt. 



Clinton, G. P. Downy Mildew, Phytophthora Phaseoli Thaxt., of Lima 



Beans. Conn. Agl. Exp. Sta. Rept. (1905): 278-303. pis. 20-22. 

 Halsted, B. D. The Downy Mildew of Lima Beans. N. J. Agl. Exp. Sta. 



Built. 151 : 18-24. figs. 6-g. 1901. 

 Sturgis, W. C. The Mildew of Lima Beans (Phytophthora Phaseoli Thaxt.). 



Conn. Agl. Exp. Sta. Rept. (1897): 159-166. (Also Bot. Gaz. 25: 191- 



194. 1898.) 

 Thaxter, R. Mildew of Lima Beans (Phytophthora Phaseoli Thaxt.). Conn. 



Agl. Exp. Sta. Rept. (1889): 167-171. 



Occurrence. Since the discovery of this fungus, in 1889, near 

 New Haven, Conn., it has been, nearly every year, of sufficient 

 importance to merit special attention in some one or more of the 

 North Atlantic States, and it is also reported from Russia. It is 

 found upon dwarf and pole sorts of the lima bean, Phaseolus 

 lunaUts, and has been reported on no other host. The fungus is 

 more commonly observed upon the pods, but it also attacks buds, 

 leaves, and shoots. Upon the pods conspicuous patches of the white 

 conidiophores are produced, mostly on the side least protected 



