314 MANUAL OP TREE DISEASES 



resembles. One of the main differences noted in the field which 

 will distinguish this blight from frost-injury (see page 12) is 

 that not all the twigs of a given tree are uniformly affected. 

 Also the more or less definitely affected areas in the seed-bed 

 point to its spread from an original center of infection. Al- 

 though this disease has not been found in this country on older 

 trees, the symptoms are included in this discussion and are 

 not materially different from the effect produced in seedlings. 



Symptoms. 



The blight becomes apparent in seedlings and on older spruce 

 trees early in the spring while the tissues of the rapidly growing 

 shoots and new leaves are succulent. Infection may take 

 place at any point in the new growth, usually at some distance 

 back from the tip. The affected area of the shoot turns brown 

 and shrivels and the leaves die and fall off. The shoot is 

 weakened at the point of infection and the weight of the still 

 healthy tip causes it to bend over. Infection may occm* at the 

 base of the new shoot and the entire shoot will droop. The 

 diseased condition soon advances the entire length of the shoot, 

 however, and the leaves are shed. The com-se of the disease is 

 confined to the period of two or three weeks after the new growth 

 is completed. Small black pustules break through the dead 

 bark or appear at the leaf-scars during the summer. 



Cause. 



Twig-blight of spruce is caused by the fungus Ascochyta 

 piniperda, formerly called Septoria parasitica. Only the conidial 

 stage is known and this appears on the dead twigs. The spores 

 are formed in the black fruiting-bodies mentioned above. Pre- 

 sumably these spores over-winter and produce primary infection 

 of the new growth the next spring. Some ascospore stage may 

 be expected to be found on the dead needles or cast-off twigs on 

 the ground and these spores may also function in carrying the 



