Vegetable and Field Crops 183 



Spraying with strong Bordeaux mixture, 4-5-50, with 

 two pounds of lead arsenate powder added is recommended. 

 Diseased vines should be pulled and burned, rotation prac- 

 ticed, and in general the suggestions given under soil dis- 

 eases (p. 26) should be followed. 



Timber-rot '"^^ {Sdcrotinia libertiana Fcl.). — Upon cucum- 

 l^ers and other cucurbits under glass this disease occasions 

 serious loss. It is rare out-of-doors. The first indication 

 is the appearance of a dense mass of white mycelium near 

 the nodes of the stem which is still green. As the disease 

 progresses the stem shrinks and yellows, the softer parts 

 decay, and the stem finally dries up. In the interior of af- 

 fected stems the white mycelium, and later near the nodes 

 or in the external mycelial masses, smooth, slender, black 

 sclerotia may be found. The germination of the sclerotia, 

 described under lettuce drop (p. 197) results in immense 

 numbers of spores. These falling upon dead tissues germinate 

 and form a mycelium which attains such vigor as to enable it 

 to attack healthy tissue and rapidly destroy it. 



To control this disease all infected plants should be de- 

 stroyed by fire before they have had opportunity to form 

 sclerotia, and the places from which they are taken should 

 be sprayed with a heavy application of some fungicide. 



Leaf-blight -^'' (Alternaria hrassicce (Berk.) Sacc. var. 

 nigrescens Pegl.). — Leaf -blight and downy-mildew are the 

 most destructive diseases of the muskmelon in this country. 

 In Florida, in some seasons, nearly the whole commercial 

 crop is lost. Much damage has been reported from Ohio, 

 Indiana, and Colorado. 



Leaf-blight begins as small, round, brown spots usually 

 marked by concentric rings. In the centers of these spots 

 the hyphse develop a moldlike growth. The spots enlarge, 

 to a centimeter or more, coalesce, dry, and cause the leaf to 

 curl and shrivel at the margin. The petioles and veins are 

 also affected. Ripening of the melons is hastened, but the 

 quality is destroyed, the fruit becoming soft, wilted, insipid, 

 and valueless. 



