Oct 21, I918 



Angular-Leaf Spot of Cucumber 



209 



rainy period. Experimentally infection was secured by placing recently 

 infected leaves on the ground beneath healthy plants on a day when 

 there were frequent showers. In the fields at Madison newly infected 

 spots appeared in abundance within five or six days after heavy rains, 

 especially the rains of July 19 and August 3-5. Rain must fall at rela- 

 tively frequent intervals to be effective in spreading the disease. Pro- 

 longed rainless periods check the development of the disease to a great 

 degree, especially if accompanied by high temperatures (PI. 15, C). 



The importance of rain in the development of the disease was clearly 

 shown at Ripon, Wis., in 1914. Owing to favorable rainy weather early 

 in the season angular-leafspot spread throughout certain fields. Two 

 of the infected fields at Ripon and one in a neighboring locality, which 

 were visited on August 11 and 12, presented a striking appearance. 



The vines were so grown together as to nearly cover the ground, but 

 the centers of the rows were clearly marked by the old, angular-spotted 

 leaves in contrast with the healthy green of the later growth which had 

 developed after the last heavy rain. 



Further evidence regarding the importance of rain in relation to the 

 development of the disease was furnished by a comparison of conditions 

 at Madison and Ripon, Wis., in 191 6. The striking difference in the 

 amount and distribution of rainfall for the two places during the month 

 of July can be seen in Table I. 



Table I. — Dates and amounts of rainfall at Madison and Ripon, Wis., in July, igi6 



The time of planting and the earlier weather conditions were similar, 

 and so it is highly probable that the disease appeared in both localities at 

 about the same time, noted first at Madison on July 3. At the end of 

 the month the disease was widespread and affecting leaves of all ages in 

 the Madison fields, while at Ripon only the older leaves at the hill centers 

 showed the angular spots. 



The relation of wind to dissemination by rain spattering has not been 

 studied experimentally, but the comparison of the way the disease 

 spread in differently situated fields throws some light on the question. 



