Vegetable and Field Crops 187 



to be susceptible, but the disease is not identical with those of 

 bean, tobacco, tomato. Mosaic is regarded as the most 

 serious disease of the cucumber in the Middle West, and it 

 ranges from California to Virginia and Texas. Mosaic on 

 squash and pumpkin appears to be a distinct disease. 



Powdery-mildew -•^■^ {Erysiphe polygoni DC). — ^This mil- 

 dew on cucurbits generally has the common characteristics 

 of the powdery-mildews, a whitish flourlike coating upon the 

 leaves and stems; at first in circular spots, but later diffuse. 

 Its presence on cucumbers in America was first announced 

 by Humphrey. It has since frequently been observed in the 

 field and occasionally under glass. 



The fungus appears chiefly upon the upper leaf surfaces 

 and is most developed upon the older leaves. It renders the 

 fruits bitter and distorts them. If it occurs in the greenhouse, 

 flowers of sulfur applied to the hot water or steam pipes in the 

 form of a i:)aste is useful. 



Stem-end-rot -''^ {Diplodia sp.).- — In transit watermelons 

 often shrivel and develop a wet, slimy rot, which may progress 

 lJ/2 inches in a day. Many cars reach their destination with 

 75 to 95 per cent of their contents spoiled. In one day 100 

 cars showed an average of 25 per cent loss. Diseased refuse 

 should be destroyed, clean culture and deep plowing practiced, 

 and cutters in harvesting must avoid spreading the contagion. 

 It is recommended that the freshly cut stem-end be coated 

 with an antiseptic paste; hot water, 3)^ qts., copper sulfate, 

 8 oz.; add to starch paste, 4 oz. to 1 pt. of cold water. 



Leaf-blight, fruit-spot "^^ (Cladosporium cucumerinum E. 

 & A.) . — This spotting on cucumbers was first noted at 

 Geneva, N. Y., in 1887, where it was so abundant as to 

 ruin the pickle crop. It is occasional on melons. 



The spots begin, when the fruit is only 2-5 cm. long, as gray, 

 slightly sunken areas with delicate, velvety surfaces. They 

 are about 3 mm. in diameter, but coalesce into irregular 

 patches, particularly toward the flower end. As the spots 

 age they darken to greenish black, and a gummy exudate 

 often appears. 



