Vegetable and Field Crops 213 



turity. On young plants the disease often assumes the 

 character of damping-off. 



Aside from the pea this disease attacks alfalfa, bean, and 

 hairy vetch. It was a grave menace in Europe in 1894, in 

 Canada in 1903, in Ohio in 1904. In New York, in 1906, from 

 50 to 80 per cent of the crop was injured. 



Two years' rotation in nonsusceptible crops lessens the 

 evil. Diseased seed should be avoided. 



Bacterial-blight -'^' (Pseud ornonas pisi Sack.). — The stems 

 are discolored, watery, olive-green to olive-brown; the leaflets 

 and stipules appear bruised and yellow. The disease is 

 known in Colorado, Nebraska, Dakota, and Utah, and in 

 severe outbreaks has been known to kill 30 per cent of 

 the plants. 



Wilt (Fusarium sps.). — Two wilts, both due to Fusarium, 

 have been described. They agree essentially with the de- 

 scription under cowpea. 



Minor diseases 



Powdery -mildew (Erysiphe polygoni DC.) develops most 

 conspicuously late in the season, and sometimes becomes so 

 injurious that the plants do not mature seed. Though it is 

 not usually very destructive, 20 per cent injury has been 

 reported from Ohio; 33 per cent from some parts of Nebraska. 

 The fungus hibernates in seed derived from affected pods. 

 Such seed should not be used for planting. Liver of sulfur or 

 Bordeaux mixture is effective in the field. 



Black-mold (Pleospora pisi (Sow.) Fcl.). — Frequently 

 moldy, black spots are noted upon pea pods, leaves, or other 

 parts. This condition is chiefly a secondary disease following 

 some other injury. 



Stem-rot (Corticium vagum) is somewhat injurious, as is 

 also the Root-rot {Thielavia), and Root-knot (nematodes). 



Damping-ofif. See p. 19. 



Rust is rare on pea. See bean. 



