340 VEGETABLE FORCING 



Downy Mildew (Peronoplasmopara Cubensis (B. & 

 C.) Cl.) is a fungous disease that attacks the leaves of cu- 

 cumbers. The angular, yellowish spots are followed by the 

 yellowing of the entire leaf and, if the infection is severe, 

 the death of the plant may occur. The cucumbers on dis- 

 eased plants are small and inferior in quality. Under 

 favorable conditions the disease develops and spreads to 

 other plants with marvelous rapidity. It is one of the most 

 destructive enemies of greenhouse cucumbers. Insufficient 

 light and sunshine, high temperatures and high humidity 

 are the conditions which are most favorable to the rapid 

 development and dissemination of this fungous trouble. 

 Spraying with bordeaux mixture is valuable, but sanitary 

 measures and the proper regulation of cultural conditions 

 are most important. 



Powdery Mildew (Erysiphe Cichoracearum, D. C.) is 

 often destructive to greenhouse cucumbers when conditions 

 of heat, light and moisture are favorable to the progress of 

 the disease. This disease makes its appearance on the upper 

 surface of the leaves, where the fungus produces a super- 

 ficial growth which is powdery white in appearance. Severe 

 attacks cause the plants to become sickly and finally to die. 

 Bordeaux mixture, applied promptly and thoroughly, is 

 valuable in checking the ravages of this disease. 



A bacterial wilt (Bacillus tracheiphilus, Smith) is often 

 found on greenhouse cucumbers. Most entomologists 

 believe that the disease is transmitted by the cucumber 

 beetle and the squash bug. The disease causes the plants 

 to wilt as if they were suffering from the lack of water, 

 and they finally die. 



Another wilt (Fusarium niveneum, Smith) is also fairly 

 common in the greenhouse. It is a fungus which works 

 internally in the stem of the plant and finally closes water 

 vessels, thus interfering with the functions of the stem, 

 causing the plant to wilt and die. This disease is also trans- 

 mitted by the cucumber beetle and squash bug, and war 



