FATE AND EFFECT OF ARSENIC APPLIED AS A SPRAY 

 FOR WEEDS 



By W. T. McGeorge, 

 Chemist, Hawaii Agricultural Experiment Station 



INTRODUCTION 



In certain districts of Hawaii during the rainy season cultivation is 

 impracticable, because of its bad effect upon the texture of the soil. 

 Yet at times this season is abnormally long and especially favorable to 

 the growth of weeds. Weed control is therefore a very important prob- 

 lem for Hawaiian planters. In experiments at the Hawaii Experiment 

 Station * it was found that the most economical means of weed control 

 under such conditions lay in the use of chemical sprays. Careful com- 

 parative tests were made of such chemicals as sodium arsenite, ferrous 

 sulphate, carbon bisulphid, etc. Of these, sodium arsenite proved by 

 far the most effective and was recommended for use. Sodium arsenite 

 sprays have now been used in Hawaii for weed eradication for about five 

 years and have proved to be efficient and economical. Such sprays 

 have not only been used to replace hand labor in the fields, but also as 

 a means of ridding grass lands of undesirable plants. 



In view of the possible injury to soils and crops as a result of the 

 continued use of such sprays, the Hawaii Experiment Station undertook 

 a study of the fate in the soil of the arsenic so applied and its influence 

 upon plant growth and upon ammonification and nitrification. 



EFFECT OF SODIUM ARSENITE ON PLANT GROWTH 



Apparently there is little or no immediate danger to crops from the 

 use of sodium arsenite as a spray. In fact, in experiments with millet, 

 buckwheat, and cowpeas grown on three different types of Hawaiian 

 soils it was found that small quantities of arsenic stimulate plant growth. 

 However, analyses of the plants did show that the arsenic is assimilated 

 and that when it is present in the tissues in sufficient concentration 

 death of the plant results. 



The most surprising feature of the investigation was the influence on 

 the ammonifying and nitrifying bacteria. In one type of soil ammonifi- 

 cation was stimulated even by such excessive amounts as i per cent of 

 arsenic (AsjOj) in the soil. The results as a whole indicate that no fear 

 need be entertained regarding any detrimental influences toward the 



' Wilcox, E. V. Killing weeds with arsenite of soda. Hawaii Agr. Exp. Sta. Press Bui. 30, 15 p. [1911.] 

 Krauss, F. G. Suppression of weeds among pineapples by arsenite of soda spray. Hawaii Agr. Exp. 



Sta. Press Bui. 48, 8 p., 2 fig. 1915. 

 McGeorge, W. T. The efifect of arsenite of soda on the soil. Hawaii Agr. Exp. Sta. Press Bui. 50, 



16 p., 3 fig. 1915. 



Journal of Agricultural Research, Vol. V, No. n 



Dept. of Agriculture, Washington, D. C. Dec. 13, 1915 



be B— 7 



(459) 



