New York Agricultural Experiment Station. 69 



great as to cause many growers to abandon the crop. Anthrac- 

 nose and the bacterial or wilt disease have been responsible for a 

 part of the damage, but the greater part of it has been caused by 

 the downy mildew, Plasmopara cubensis (B. & C.) Humph. The 

 latter fungus made its first appearance 1 in the United States in 

 1889, since which time it has spread so rapidly that it has become 

 one of the most destructive diseases of late cucumbers. It now 

 occurs quite generally throughout the northeastern United States 

 as far west as Ohio, where it has been very destructive, 2 and ap- 

 pears to be spreading westward. No special effort has been made 

 to determine its distribution in New York, but reports indicate 

 that it is in nearly all parts of the State, although there are still a 

 few localities where it is unknown. Besides the previously men- 

 tioned localities in southeastern New York we have, during the 

 past season, personally observed it at Albany and Geneva, where 

 it was destructive. There are no indications of its abatement; on 

 the contrary, it seems to be steadily advancing. In localities 

 where it has previously occurred it may be expected to reappear 

 to a destructive extent the coming season, and localities in which 

 it has not yet occurred cannot reasonably expect to remain much 

 longer exempt from its ravages. However, the amount of dam- 

 age which it does depends very largely upon the temperature be- 

 tween July 15 and August 15. A high temperature and frequent 

 light rains during this period furnish ideal conditions for the 

 propagation of the fungus. 



PREVIOUS EXPERIMENTS. 



In 1896. — In 1896 the Station made an experiment 3 in which 

 it was shown that this downy mildew can be prevented by spray- 

 ing the plants with Bordeaux mixture. 



1 Halsted, B. D. Some Notes upon Economic Peronosporeae for 1889, in 

 New Jersey. Journal of Mycology, 5 : 201. 



2 Selby, A. D. Prevalent Diseases of Cucumbers, Melons and Tomatoes. 

 Ohio Agr. Exp. Sta. Bui. 89. D. 1897. 



3 The details of this experiment are reported in Bulletin 119. The Downy 

 Mildew of the Cucumber : What It Is and How to Prevent It . 



