174 Journal of Agricultural Research voi. iv. no. 2 



From 44 plate cultures exposed (2 plates at a time) for 15 to 30 minutes 

 near the open ground surface in various beet fields at different times 

 from June 7 to September 10, 1912, inclusive, at Rocky Ford, Colo., 

 50 colonies of P. hetae were obtained. The fungus was present in the 

 air at temperatures which varied from 68° to 115° F. at the ground 

 surface, with relative humidities from 39 to 71 per cent. These read- 

 ings were taken during the time that the plates were exposed. The 

 organism was not obtained from plates exposed during one night, an 

 experiment which was of necessity limited. Its presence in the air 

 seemed to be dependent on the humidity, a high humidity apparently 

 causing the pycnidia to expel their spores, while a subsequent decrease 

 in the relative humidity caused the spores to escape into the air. 



At certain times P. hetae occurs abundantly in irrigation water. This 

 is particularly true late in August and early in September. The pyc- 

 nidia are well formed on the leaves by this time, and if moistened they 

 burst and many spores are expelled. Samples of irrigation water 

 which was either standing between the rows or had drained to the lower 

 portions of the beet fields about one day after irrigation yielded Phoma 

 in several cases in the tests made in 191 2. Thirty-three colonies of P. 

 hetae in plate cultures were obtained from 23 c. c. of water representing 

 four such samples, while 3 c. c. of water flowing through a field yielded 

 nine colonies in cultures. 



Three species of insects have been found to be carriers of the fungus to 

 only a slight extent. Two culture tests made with the moth of the beet 

 webworm, Loxostege sticticalis L., yielded many colonies of P. hetae in the 

 latter part of July, while cultures made at later intervals gave negative 

 results. Several tests made of the alkali beetle, Monoxia juncticoUis 

 Say, and the larvae of the woolly bear (yellow), Diacrisia virginica Fab., 

 yielded only a few colonies of the fungus. 



Phoma hetae may occur in abundance in the dung present in feed yards 

 where beet tops have been fed. It is not to be concluded that the pres- 

 ence of the organism here indicates that it can survive a passage through 

 the alimentary tract of cattle or sheep, but rather that the fungus is 

 viable in dung after the ordinary method of feeding beet tops where they 

 are not entirely consumed. In one test made early in January, 1913, 

 36 colonies of P. hetae were obtained from nine small drops of strong 

 manure decoction. 



FACTORS INIMICAL TO VIABILILITY OF PHOMA BETAE IN BEET 



LEAVES 



DRY HEAT 



The thermal death point of Phoma hetae in sugar-beet leaf tissue exposed 

 for half an hour to dry heat is between 80° and 90° C. Seventy isolations 

 of Phoma hetae were made from spots on leaves exposed at 70° for half 

 an hour. At 80° two colonies developed in cultures made from approxi- 



