228 DISEASES OF TROPICAL PLANTS 



CH. 



The organisms are carried from season to season in 

 the seed and in the soil. When a field is once in- 

 fected the organism gains entrance to healthy plants 

 through wounds. The only consistent method of 

 control which can be recommended at this time is the 

 careful selection of seed and the rotation of crops. 



Downy Mildew. This disease is due to Phytoplithora 

 phaseoli, Thax., and thus far has been reported only 



FIG. 81. Beans affected with anthracnose, Colletotrichum lindemuthianum. 

 (Photo by C. W. Edgerton.) 



from Northern United States and Eussia. Whether 

 it will prove to be a strictly northern parasite or will 

 follow the lead of its close relative, Phytophthora 

 infestans, De Bary, of the potato (page 208), and work 

 into the warmer climates remains to be seen. This 

 possibility makes it worthy of brief mention at this 

 time. It is most abundant on the pods, but will attack 

 any part of the plant above ground. On the pods it 

 causes prominent patches, containing abundant coni- 

 diophores, and finally causes a wilting and dying of 



