4 CIRCULAR 409, U. S. DEPARTMENT OF AGRICULTURE 
Barnum (1) showed that the concentration of thallous sulphate 
proving effective was 1 pound per 1,000 pounds of grain, or one-tenth 
of the concentration needed for effective control in California. He 
furnished the following statement: : 
The observed and much heralded destruction of vegetation which has been 
reported from Hawaii was induced unintentionally by myself as follows: At the 
request of Dr. H. L. Lyons of this Station, poison bait was prepared in July 
1931, to control a small population of mongoose in the Manoa Arboretum. 
These animals threatened extinction of a number of imported birds released 
sometime prior in this region. The preparation was made by mixing 1 lb. of 
ground fresh meat with 32 gms. of TlSO,. From the mixture torpedoes, each 
containing 1 full spoon of the mixture, were made of small sheets of paper. The 
torpedoes were distributed in suitable places, near wooden markers, in the 
Arboretum. Some were eaten; others remained and decomposed in the grass, 
kept green by the daily rains. Small areas of grass surrounding these uneaten 
torpedoes were killed and the areas remained denuded for several months. I 
have never seen the same effect following thallium-wheat applications in corn- 
fields. The dosage in the meat balis was much higher than that commonly used 
in treatment of grain. The protein mixture may have been toxic in itself. 
A small test was laid out wherein 0—-5-10—-15 gms. of Tl,SOs per L. of water 
were applied to grass spots of approximately 1 sq. yd. each, but no permanent 
toxic herbicidal values were obtained. 
Of personal communications received from a number of individuals 
who have used thallous sulphate mixtures, a typical report is that of 
John T. Moir, manager of the Koloa Sugar Co., Koloa, Hawaii: 
We have never noted any damage to field crops attributable to the thallium- 
sulfate-poison rat baits. The bulk of our rat bait is distributed along field edges. 
As a result the same areas have received repeated doses although not in the 
same exact spot, perhaps. No killing of vegetation has been noted. In fact, 
weeds continue as strong as ever. ; 
While this investigation was in progress, Crafts (8) published an 
abstract of his studies on the effect of thallous sulphate on four Cali- 
fornia soils. He found that soils varied in their power of fixing thal- 
lum. Thalgrain had no effect on the germination or growth of oats 
one-half centimeter away; if one-fourth centimeter away, growth was 
reduced. ‘‘Except where the dosage was excessive, oat seedlings were 
unaffected by the application of treated barley to the soil, followed 
by irrigation.”’ The heaviest application, equivalent to 27 pounds of 
thallous sulphate per acre, reduced growth less than 50 percent. The 
application of 5,000 pounds of poisoned grain per acre might sterilize 
the top 1.5 inches. However, the average initial dosage of poisoned 
erain is only one-third pound per acre, and this is decreased later to 
one thirty-fifth pound or less. He concluded: 
The success of this material should permit similar reductions in other regions, 
so that the amount of chemical becomes totally insignificant so far as soilsteriliza- 
tion is concerned. The writer observed no loss in fertility in range lands success- 
fully treated for 5 successive years. The only denuded areas found were the 
open burrows, fresh mounds, and beaten trails of squirrels in untreated fields. 
Regardless of other objections to thallium compounds in rodent control, the 
possibility of losing agriculturally valuable land through sterilization seems 
remote. 
EXPERIMENTS 
In order to determine the effect of thallium on plant growth under 
controlled conditions, a double investigation was undertaken, one 
part in the laboratory and the other in the field. : 
2 Personal communication, Sept. 12, 1933. 
3 Personal communication, Apr. 2, 1932. 
