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 1 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 (As 2 0 3 ) in the soil. The results as a whole indicate that no fear 
need be entertained regarding any detrimental influences toward the 
1 Wilcox, E. V. Killing weeds with arsenite of soda. Hawaii Agr. Exp. Sta. Press Bui. 30, is P- [1911J 
Krauss, E. 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 effect of arsenite of soda on the soil. Hawaii Agr. Exp. Sta. Press Bui. go, 
16 p., 3 fig. 1915. 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
be 
(459) 
Vol. V, No. 11 
Dec. 13, 1915 
B—7 
