SWEET PEA DISEASES AND THEIR CONTROL 137 



what more abundant when the plants have passed all usefulness. 

 The writer had the opportunity of collecting specimens at random 

 from six large houses, and from three acres of outdoor sweet peas in 

 Massachusetts and from a similar three acre plantation in Penn- 

 sylvania. So far, the writer has only met with the conidial or 

 oidium stage. On our own sweet pea field, we have carefully 

 watched for a perithecial stage but without success. Late in the 

 fall, badly infected leaves have been collected and put away to 

 winter over, but that material has failed to develop perithecia. 



Recently Blodgett ^ claimed to have found the perfect stage of 

 this mildew, which he referred to the species Microsphera aim 

 (Wallr.) Salm. . 



Physiological Troubles. 



These troubles are usually induced by improper conditions of 

 the soil. Root burn, for instance, may be induced by the excessive 

 use of wood ashes applied with the manure. It is not uncommon 

 for growers to use wood ashes at the rate of 1500 lbs. to 4500 

 square feet of bed space. This would be equivalent to nearly 

 seven and one-half tons per acre. Under such conditions the roots 

 actually burn up because of the strong alkalinity of the soil. More- 

 over hard-wood ashes contain about 30% caustic lime and from 5 

 to 12% potash. Both of these elements in excess in soil render it 

 too alkaline for plant growth. To remedy this trouble, use acid 

 phosphate followed by a good drenching of water. This will help 

 to neutralize the alkalinity and restore the balanced food ration. 



Bud drop. As the name implies the young flower buds at a 

 very early age turn yellow and drop off. This drop should not be 

 confused with the drop produced by the anthracnose disease. 

 In the latter case, the flower develops into a normal spike but it is 

 attacked soon by the fungus Glomcrella rufomaculans which girdles 

 it at a point of attachment between the flower and the peduncle. 

 Here the flower often drops off, leaving behind the beheaded 

 peduncle. In the latter case, however, the minute young flower 

 bud never develops, instead it turns yellow and drops off. There 



1 Blodgett, F. M. Sweet pea Powdery mildew. Phytopath. 5: 237, 1915. 



