350 Diseases of Economic Plants 



(Lag.) Arth.) is reported on the leaves from Florida, Cuba, 

 Porto Rico, and British Guiana. Cluster-cup-rust {Mcidium 

 gossypii E. & E.). — An outbreak of this disease occurred in 

 southern Texas in 1917, causing large defoliation, with an 

 estimated loss in yield of 20 per cent. It is conunonly present 

 in the South to a degree, but usually does not assume destruc- 

 tive proportions. Crown-gall {Pseudomonas tumefaciens) 

 does some injury. 



Mosaic, black-rust. — The first signs of this disease are 

 yellowish spots which give the leaf a checkered appearance. 

 The discoloration occurs first in small areas, which are 

 roughly rectangular owing to limitation by the veins, and 

 which are situated at jioints most remote from the main feed- 

 ing veins. Usually the centers of these spots soon turn 

 brown, and the brown part enlarges and shows a series of 

 concentric markings. In later stages these weakened areas 

 may be overgrown by Alternaria or other saprophytic fungi. 

 If very dark-colored fungi grow upon these spots, they soon 

 become black-coated and take the popular name "black 

 rust." 



Kainit, used as fertilizer, often reduces the damage from 

 mosaic. 



Red leaf-blight. — This reddening, resembling autumnal 

 coloration, occurs most frequently toward the season's end 

 and is most common upon poor soil. It is due chiefly to 

 lack of nourishment. 



Attack of mites produces a similar appearance. 



Shedding. — This occurs chiefly following extremes of 

 either dry or wet weather or following a change from one ex- 

 treme to the other. 



FLAX 



Wilt ■'^"'^ {Fusarium lini Bolley). — A condition of soil 

 known as "flax sick" has prevailed in many sections of the 

 country to such an extent as to cause the abandonment of 

 flax culture. This is notably true in Iowa, Minnesota, North 



