May 15, 191S Phoma Betae 



175 



mately the same amount of material, and at 90° and 100° none were 

 obtained. It is evident, therefore, that the fungus would be rendered 

 harmless when infected beet tops are dried in a pulp drier. 



OVERWINTERING UNDER FIELD CONDITIONS 



Phoma hetae has been found to be present to a slight extent in the soil 

 of old sugar-beet fields. It was isolated from samples of finely divided 

 soil taken during March and April, 191 2, from fields near Rocky Ford, 

 Colo., which had been in sugar beets for several years. Four colonies 

 were obtained from 0.05 gm. of a surface sample, while from cultures 

 made from 0.25 gm. representing two different first-foot samples eight 

 colonies were obtained. No growth of the fungus occurred in cultures 

 made from second- and third-foot samples. Although the tests were 

 continued throughout May, June, July, and the first part of August, 

 no further isolations were made. 



About the middle of October, 191 2, sugar-beet leaves which were 

 infected with P. hetae were mixed with soil to the depth of 6 inches in a 

 box and left exposed to outdoor weather changes. No cultures of the 

 organism could be obtained from these leaves after 3 months. However, 

 different results were obtained when the leaves were buried at various 

 depths in the ground. It was found that the fungus was viable at the 

 end of 3 months in leaves which had been buried at depths of i to 5 

 inches or had been kept in the interior of a pile of hayed beet leaves. 

 The organism w^as isolated from leaves buried at depths of i to 5 inches 

 after 5 months, but there was no development from the leaves buried 6 

 to 8 inches. At the end of 12 months no growth of P. hetae was obtained 

 at any depth, and the leaves were practically all disintegrated. How- 

 ever, the viability of the fungus was not impaired in dried leaves stored 

 under herbarium conditions for over 2 years. 



The maximum temperature of the air from October, 191 2, to September, 

 1913, inclusive, the time of the overwintering experiment, varied from 

 4° to 102°, the minimum from —20° to 72° F. The maximum tempera- 

 ture of the ground at a depth of 5 inches from December, 191 2, to May, 

 1913, inclusive, varied from 42° to 92°, the minimum from 22° to 51° F. 

 During the 12 months of the experiment there was 9.34 inches of rainfall 

 and snow, mostly during April, May, June, and July. There was no 

 precipitation during November and December of 191 2, but there occurred 

 0.2 inch in January, and 0.4 inch m October, 191 3. During this time the 

 lowest soil and air temperatures were registered. 



It appears, then, that the results on the viabihty of the organism 

 obtained from covering the leaves with soil in boxes are not comparable 

 to those obtained under field conditions. The temperature of the air 

 varies from that of the soil to such a degree that accurate results for 

 field comparison can not be obtained in such an experiment. A period 

 of one year seems sufficient to eliminate Phoma bctae from infected beet- 

 leaf material left in the field, although there is a probabiUty that the 



