210 AXNUAL REPORTS 01>" DEPARTMENT OF AGRICULTURE. 



A study of the ability of the sweet potato to foini a ptotective cover- 

 in<j: over wounds and the factors that infliu'iuv this healing process 

 has been made. Tlie ellec'tiveness of the healed surface in preventing 

 infection has been investigated and is being given further study. 

 An improved method for the disinfection of sweet potatoes for bed- 

 ding has been worked out. Heretofore, in the absence of sufficient 

 experimental data, it has been recommended that the mercuric- 

 chlorid solution be discarded after 3 or 4 bushels of potatoes have 

 been treated. It is now known that by adding two-fifths to one-half 

 ounce of the chemical after each 10 bushels have been treated, 50 

 bushels may be treated before it is necessary to discard the solution. 

 A considerable saving in time and money is thus made possible for 

 the grower. 



CLOVER NEMATODE. 



Investigations have been inaugurated during the past year of the 

 nematode {Tylenchus dipsacl), which has become a serious pest 

 of the clover crop in the Pacific Northwest. This nematode has been 

 found to be responsible for extensive damage in the large seed- 

 growing areas of red clover in Idaho and other Northwestern States, 

 and there is danger that it may be carried to the important red-clover 

 growing sections of the Central and Eastern States, to which hun- 

 dreds of carloads of clover seed are shipped annually from the in- 

 fested localities in the West. It has been definitely proved that the 

 disease can be carried on the seed and that infection of the plant can 

 occur by this means. This nematode also attacks many other plants, 

 to some of which it causes serious injur3\ The investigations of the 

 trouble are conducted in cooperation with the Idaho Agricultural 

 Experiment Station, with field headquarters at Jerome, Idaho. They 

 include studies of the symptoms, methods of infection, distribution, 

 and methods of control. A preliminary survey has been made in 

 Idaho, and a successful method of seed treatment has been found. 



CASTOR-BEAN DISEASES. 



Investigations of castor-bean diseases, which were undertaken in 

 1918 at the request of the War Department, were brought to comple- 

 tion within the past year. Major attention was given to the gray 

 mold, or spike blight, which was found to be the cause of serious 

 losses in the castor-bean plantings, comprising 100,000 acres or more, 

 in the Southern States. The life history of the fungus causing this 

 disease, which was found to be a hitlierto undescribed species of 

 Botrytis, was completely worked out, including the discovery of its 

 perfect stage. Observations were made on the effect of temperature 

 and moisture on the dcvelopm.ent of the disease in the field, and an 

 extensive series of control ex))eriments was carried out and practical 

 recommendations given to the growers. It was determined definitely 

 that the disease originated in seed imported from Bombay, India. 

 The wilt disease of castor bean, also found to be destructive in 

 Florida, was studied, its cause determined, and a number of field 

 experiments looking toward the relationship of different conditions 

 of the soil to the disease wei'e carried out. 



