ANNUAL REPORT, 1946-47 45 



subirrigated. However, even though sand top-watered was comparable to Ver- 

 miculite in percentage of cuttings rooted, the roots formed in the Vermiculite 

 were 50 percent greater in length and more numerous on individual cuttings. 

 Initiation of roots on cuttings in the Vermiculite does not appear to occur sooner 

 than in sand, but roots grow much more rapidly once they are formed. This 

 striking difference in rate of growth between roots produced in the two media 

 probably is due to a more uniform supply of available moisture to the roots in 

 Vermiculite. Also, there is better aeration due to less tendency of the Vermiculite 

 to pack. 



Since cuttings transplanted from a rooting medium such as Vermiculite have 

 roots with thinner cellular tissue, the soil into which the roots are placed must be 

 kept more moist until they have become established in it. 



Dusting China Asters witti Insecticides for Control of Yellows. (Harold E. 

 White, Waltham.) During the summers of 1945 and 1946 various kinds of 

 insecticidal dusts were applied to China Asters under field conditions to deter- 

 mine the effectiveness of such treatments in control of leafhoppers which carry 

 the yelloup disease. 



In 1945, test plots were dusted at 7 to 10 day intervals with a 2}^ percent 

 DDT-sulfur dust and a 5 percent DDT-sulfur dust. Two formulations of each 

 of these dusts were used, one being a fused DDT-sulfur and the other a mechanical 

 mixture of DDT-sulfur. 



The treatments in 1946 were along similar lines with 1 percent DDT, 3 percent 

 DDT, sabadilla 10 percent, pj'rethrum dusts, and a formulation known as X 

 155 which contained 12 percent nicotine and 7 percent DDT. 



Tests made with these different insecticidal materials on living leafhoppers 

 confined in a cage showed them to be toxic to the insects. However, the field 

 tests made by dusting China Aster plants in the open yielded no significant data 

 Insofar as reduction of the yellows disease was concerned. Apparently these 

 dusts, as used under field conditions, were not sufficiently repellent to prevent 

 leafhoppers from feeding on plants and transmitting the yellows virus. 



From these tests, it would seem that Insecticides applied to asters in order to 

 control yellows must be of a highly repellent nature to keep the leafhoppers 

 from the plants. 



DEPARTMENT OF FOOD TECHNOLOGY 

 C. R. Fellers in Charge 



Incidence of Home Canning Spoilage Bacteria in the Soil. (W. B. Esselen, 

 Jr., G. K. Lycarzyk, and C. R. Fellers.) During the summer of 1945, 325 samples 

 of soil and raw vegetables were obtained from 15 gardens of Amherst and vicinity; 

 and in 1946, 671 samples were collected from 12 gardens of the same locality. 

 The samples were examined bacteriological ly in order to study the incidence and 

 factors Influencing the incidence of thermophiles, putrefactive anaerobes, and 

 flat sour organisms, these being representative of important groups of spoilage 

 bacteria encountered in home canning. 



These three groups of bacteria showed considerable variation in numbers 

 during the season. Rainy weather seemed to favor their development. In 

 general, the number of thermophiles present in the soil samples greatly exceeded 

 the numbers of putrefactive anaerobes and flat sour organisms. Gardens treated 



