PLANT RESPONSES TO INSECTICIDES IN THE SOIL 33 



increasing amounts of DDT in the soil, none of the amounts above 

 25 pounds produced significantly greater weight than the 25- 

 pound treatment. This result suggests that the increased growth 

 resulted from the control of some soil-borne pest rather than 

 from any direct stimulation. Even if there is no stimulation, corn 

 appears quite tolerant to the amounts of DDT used in these tests. 



The results on the two varieties of garden peas were not con- 

 sistent. The Alaska variety appeared tolerant up to the 200- 

 pound treatment, while the Thomas Laxton showed a significant 

 reduction in yield on that treatment. Both varieties showed a 

 little higher plant plus pod weights on the 25- and 50-pound plots 

 than on the controls, but further experience is needed with these 

 and other varieties of peas to help evaluate these data. 



Beans, cabbage, and potatoes from certain plots in the field and 

 beans from the coldframes were cooked and tested for flavor by 

 a group of fellow workers. In a few instances samples from high- 

 DDT plots were reported by some of the judges to be somewhat 

 lacking in the characteristic flavor exhibited by the controls. 

 Other judges were unable to detect differences due to treatment. 

 No foreign or objectionable flavor was ever detected. Those sen- 

 sitive species that were seriously depressed in growth and yield 

 might well show such lack of quality as is characteristic of any 

 crop that has made very poor growth and yield because of infer- 

 tile soil, disease, insect attack, or bad weather. 



Incidentally, in this connection, we have noted no reports prov- 

 ing that DDT can enter the plant from the soil and thereby affect 

 the quality of edible portions by its presence in the tissues. Plant 

 materials from these studies have been analyzed for DDT by 

 workers in the Bureau of Entomology and Plant Quarantine. No 

 DDT was found in any of the tissues analyzed. 



GREENHOUSE STUDY OF ORCHARD SOIL 

 Materials and Methods 



One of the peach orchards at the Plant Industry Station had 

 received the recommended quantity of DDT in the spray schedule, 

 approximately 25 pounds per acre of technical DDT in wettable 

 powder, % pound per tree, per year from 1946 to 1949, inclusive. 

 In 1946 6 pounds of the gamma isomer of benzene hexachloride 

 had also been used per acre, applied in the form of technical BHC 

 in a wettable powder in two foliage sprays, and involving some 

 50 pounds per acre of the technical product. For a dozen years 

 the orchard had received lead arsenate in the spray schedule, to 

 a total of about 300 pounds per acre, and some 400 pounds of 

 zinc as zinc sulfate in zinc-lime spray. 



In the fall of 1948 there was serious difficulty in obtaining a 

 stand of a cover crop of Abruzzi rye beneath the trees of this 

 orchard, although good stands had been obtained in preceding 

 years. Growth was acceptable in the "middles" between the trees, 

 but the plants failed completely within roughly circular areas that 

 coincided with the spread of the branches. Because of the recent 

 finding that Abruzzi rye is highly sensitive to DDT it appeared 



