Nov. la, I92I Plum Blotch 369 



In 19 19, spores obtained from apple twig cultures and suspended in 

 sterile distilled water were applied to fruit, foliage, and twig of Abundance 

 plums on May 15. Where cultures originally obtained from plum fruits 

 were used, two fruits were found with two typical blotches on each of 

 them; three leaves were found with scattering spots, each spot typical 

 of the disease and each bearing a single pycnidium with the character- 

 istic spores of Phyllostida congesta. Like results were obtained by the 

 use of cultures obtained from the leaves; one fruit showed three typical 

 blotches with pycnidia and two others showed one; seven leaves were 

 successfully infected. From all these artificially inoculated parts, the 

 fungus was reisolated and proved to be P. congesta. 



No lesions were found on the twigs. 



Inoculations made upon Japanese plums with spores from pure cul- 

 tures of Phyllostida solitaria gave negative results in 1918, 1919, and 1920, 

 though the spores were applied to fruit, foliage, and twigs at frequent 

 intervals throughout the spring. 



Though the inoculation experiments herein reported upon are suffi- 

 cient to prove Phyllostida congesta the cause of plum blotch on leaves and 

 fruit and show the fungus on the fruit to be identical with that on the 

 leaves, they are not as complete as the writer should wish. All the inocu- 

 lation work was done at Arlington, Va., under conditions probably un- 

 favorable to the fungus, since it has been found naturally only in regions 

 much farther south. 



It is planned to carry on further inoculation work with both the plum 

 blotch and apple blotch Phyllostictas. The writer expects eventually to 

 obtain successful inoculations on plum twigs using Phyllostida congesta as 

 inoculum. 



CONTROL MEASURES 



No attempts to control plum blotch have been made. One would 

 expect that control might be had by spraying with a strong fungicide at 

 intervals beginning shortly after the petals have been shed as is the case 

 with apple blotch. Dilute lime-sulphur solution and Bordeaux mixture 

 injure Japanese varieties of the plum so severely as to preclude their use 

 during the growing season. It is also doubtful whether or not dilute 

 lime-sulphur solution would control severe cases of disease, since it will 

 control only mild cases of apple blotch. Self-boiled lime-sulphur can be 

 used with safety on the Japanese plum, but it is a fungicide which is 

 even weaker than dilute lime-sulphur solution. It seems probable, 

 therefore, that should this disease ever become an important one, its 

 control will present a problem of considerable difficulty, though it is 

 realized that the reasoning by analogy in which the writer has just 

 indulged may easily lead to wrong conclusions. 



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