304 Diseases of Economic Plants 



The causes of these rots have not been fully studied, but 

 they are probably due to fungi or bacteria or both. 



Minor diseases 



Spotted-blight (Macrosporium sp.). — Small black spots 

 of mold upon poorly filled grains sometimes occur, occasion- 

 ally affecting field areas of considerable size. 



Speck, pip (Saprophytic fungi and bacteria). — The grain 

 in some instances bears one or more discolored, often sunken, 

 circular areas, 1-3 mm. in diameter, bounded by dark mar- 

 gins with gray or pale-buff centers and often with a minute 

 dark spot in the very center. In other cases the grain is 

 shriveled and distorted without any definite spot. The 

 interiors of the grains are chalky and brittle, and of such 

 inferior quality as to be largely depreciated in value. Not 

 infrequently from 10 to 25 per cent of the grain is affected, 

 and in some cases nearly 100 per cent. The germinating 

 power is much reduced. 



The disease is caused by the invasion of saprophytic fungi 

 or bacteria into wounds caused by sucking bugs. Methods to 

 control these insects have not been thoroughly worked out. 



Rust (Physiological). — The leaves die gradually, begin- 

 ning with the tips of the lower ones. Red spots and streaks 

 usually appear before the leaves lose their green color. The 

 roots are poorly developed, the plants dwarfed, and the heads 

 small and light. 



RYE 



Ergot {Claviceps purpurea (Fr.) TuL). — Ergot is widely 

 known as a black or purplish body, several times larger 

 than the seed of the affected plant, which displaces the 

 ovary or grain. Ergot occurs commonly upon rye and 

 many other species of grass, as wheat-grass, wild ryes, blue- 

 joint, Kentucky blue-grass, Canada blue-grass, red-top, 

 timothy, and rye-grass. Of the last named, one farmer 

 reports 1000 tons of hay so badly affected as to be worthless. 

 Ergot is occasionally injurious on wheat. 



