654 INSECTS AFFECTING VEGETATION 



PEA DISEASES. 



Pea Blight. A close examination of the diseased plants showed 

 that the stems had been attacked at many points, frequently as high 

 as one and one-half feet from the ground, though most severely near 

 the ground where the disease starts. In the beginning, dead areas 

 were formed on the stem in the shape of oval or elongated lesions. 

 At a point from the top of the ground to two or three inches above 

 ground, these lesions were so numerous and had spread so rapidly, 

 as to become continuous, leaving the stem encircled by a dead area. 

 In some cases, the woody part of the stem was also dead, though the 

 greater number of such plants still remained green above. On the 

 leaves were orbicular or oval dead spots, one-eighth to one-half inch 

 in diameter. These areas are darker at the circumference. Below, 

 the leaves \yere badly spotted, causing them to die. In the green- 

 house experiments, the spotting of leaves failed to develop to any ex- 

 tent, though the attack at germination, and later, at the base of the 

 stem, was more severe than out of doors. In such indoor grown 

 plants, the dead areas at the base do not often extend much above 

 the surface. The base of the stem is dead and shrunken as is usual 

 when attacked below the ground. A little higher up (even with 

 the first leaf) may be seen the ordinary lesion due to the fungus. 

 The growing tip is also often attacked. This is frequently the case 

 where no trace of the disease occurs below r . The injury to the origi- 

 nal sprout or stem will cause one or more secondary shoots to appear. 

 This explains many cases of the so-called freak peas. If the injury 

 to the tip be on larger plants, a side branch may be developed pre- 

 maturely and become the leading shoot. 



These effects do not always result from Ascochyta alone, for any 

 severe injury to the stem may cause the growth of secondary shoots. 

 Such plants as are not killed by the fungus before the time of flower- 

 ing, develop pods in proportion to their vigor. The pods usually be- 

 come badly attacked and exhibit spots. (Ohio E. S. B. 173.) 



Perhaps the most important thing in connection with the life 

 history of the fungus is, that the vegetative part of mycelium, infect- 

 ing these spots of the pods, grows through the husk into the seed. 

 Frequently it grows entirely through the pod, forming similar spots 

 on both sides. When the fungus grows into the seed, brown spots 

 may be formed on the surface. In the worst cases, half the surface 

 is frequently discolored and the seed adheres to the pod. These 

 areas are much more striking on green colored peas, such as the 

 Market Garden variety, than on the yellowish varieties, such as the 

 Admiral. Pea seed may be badly affected with this fungus and yet 

 escape ordinary observation, as only the most badly diseased ones 

 will show serious spots. When the pea is exposed for a few days 

 to considerable moisture, then spots appear. 



Recommendations. The germination of such diseased seed 

 is very poor. Of those selected as being very badly affected, only 6 

 per cent germinated. It has been previously demonstrated that the 

 fungus passes over to the young plant from the seed. The severity 

 of the attack may vary very much, even when such seeds do germi- 



