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DISEASES OF ECONOMIC PLANTS 



Fig. 75. — Grape ne- 

 crosis as it appears 

 on the canes. Af- 

 ter Reddick. 



shoots and leaves exhibit a dwarfing, with 

 leaves small and often crimped about the 

 margin ; leaves of nearly normal size but 

 blanched ; apparently healthy vines with 

 leaves and fruit shriveling and dying in 

 the summer ; fleshy or corky longitudinal 

 excrescences on the stem, which in the 

 autumn dry down and become reddish 

 brown and the following spring slough 

 off ; the presence of minute black pustules 

 on a dead spur, l^ark, or wood under the 

 bark ; small reddish brown spots 3-4 mm. 

 long on the green shoots. 



The disease is conveyed to new tissue 

 by spores from the pycnidia, also pro])ably 

 by pruning tools which cut sound wood 

 after cutting into diseased tissue. It may 

 also enter the older parts through wounds. 

 Cuttings bearing the fungus prol^ably 

 sjji-ead the disease. 



Spraying shoots when from 72-15 cm. 

 long will probably reduce infection. Dis- 

 eased vines should be pulled and burned, 

 or if the root crown be still sound, they 

 may be cut back to near the ground, 

 and the renewal will be healthy. In the 

 spring and summer it is well to mark sick 

 vines for future eradication. Cut off the 

 diseased parts, using tools separate from 

 those used in ordinary pruning. 



Root rot, dematophorose (Deniatophora 

 necatrix Hartig). — This rot attacks a 



