ARSENICAL DUSTING OF CABBAGE 7 



harvest, and also on a sample of Charleston Wakefield cabbage which 

 received the last application of calcium arsenate and lime (1 to 5) 

 28 days previous to sampling. It was exceeded on plants dusted 

 with undiluted calcium arsenate 9 days, and on Stein Flat Dutch 

 dusted with calcium arsenate and lime containing 10 percent and 

 5 percent of arsenic trioxide, respectively, 8 and 15 days previous to 

 harvest. These data show that applications of arsenic must be dis- 

 continued before the appearance of the head or wrapper leaves that 

 will remain attached to the head when it is harvested for market. 

 The results of these experiments indicate that the normal arsenic 

 content of cabbage (whole plant) under South Carolina conditions 

 averages approximately 0.001 grain of arsenic trioxide per pound. 



Several factors influence the quantity of arsenical residue remaining 

 on cabbage treated with arsenicals. The stao-e of plant development 

 at the time arsenical treatments are discontinued is probably most 

 important in determining whether or not the harvested product will 

 contain an excess of harmful residue. The plant-growth study in 

 conjunction with the residue determinations demonstrated that the 

 marketable part of cabbage retaining foliage which had been exposed 

 to the arsenical treatments may contain residue exceeding the legal 

 tolerance, regardless of the period of time elapsing between the last 

 application and harvesting. Normally all cabbage treated after the 

 heads start forming (fig. 1) are included in this category. 



The quantity and character of rainfall are probably second in 

 importance. These studies show that heavy rainfall will remove a 

 large quantity of the deposits on dusted cabbage, but ordinarily not 

 enough to prevent the tolerance limit from being exceeded. 



In addition, the season of the year when the plants are grown may 

 affect the growth of the plants, with special reference to the develop- 

 ment of leaves that may or may not be retained as a part of the 

 marketed head. 



Although records were obtained regarding the insecticidal value 

 of the different treatments reported herein, it may be stated that in 

 general such records were not conclusive, since some of the applica- 

 tions were made under conditions unfavorable for maximum insec- 

 ticidal effects, and in some of the experiments the worm populations 

 were insufficient for obtaining significant results. Throughout the 

 study the worm population consisted principally of larvae of one or 

 more of the following species: The cabbage looper (Autographa 

 brassicae Riley), the imported cabbage worm (Ascia rapae L.), and 

 the diamond-back moth (Plutella maculipennis Curtis). 



SUMMARY AND CONCLUSIONS 



Twelve experiments were conducted, six at Charleston, S. C, and 

 six at Baton Rouge, La., during the seasons of 1932-33 and 1933-34 

 to determine the limitations imposed by residue on treatments with 

 arsenicals in controlling worms on cabbage. Four dilutions (lime as 

 diluent) of paris green and calcium arsenate and one dilution of lead 

 arsenate were employed in two or more of the experiments. The 

 rates per acre per application ranged from approximately 10 to 24 

 pounds, the number of applications of the different insecticides 

 ranged from to 10, and the periods of time from last dusting to 

 sampling ranged from 8 to 100 days. The samples for residue deter- 

 mination consisted of from 10 to 20 plants taken at random from each 



