6 CIRCULAR 409, U. S: DEPARTMENT OF AGRICULTURE 
procedure. In the original treatment of an infested area an average 
of 1 pound of thalgrain per acre is used for the first treatment, and 
one-fifth to one-tenth pound per acre on subsequent treatments. 
Normally 27 g of thalgrain are distributed over an area of 2 to 4 
square feet around ground-squirrel burrows. Since 1 pound of thal- 
grain is sufficient for 16 bait spots, it will actually cover 32 square 
feet, on the basis of the strongest concentration. If the entire acre 
were covered, approximately 13 pounds of thallous sulphate, or 10 
pounds of thallium, would be required. 
In March 1932, on a typical range area in Santa Clara County, 
Calif., 8 quadrats with suitable checks were established, each quad- 
rat 2 feet square. All vegetation in each was listed and mapped for 
density and for percentage of the entire vegetative growth, density 
being tabulated on the basis of 10 as complete coverage. On these 
quadrats the soil was Altamont clay loam, but comparative studies 
with other types of California soil gave identical results. 
The quantity of thalgrain applied to each quadrat and the thallium 
content are given in table 2. There was no rain from March 1932, 
when the thalgrain was distributed, until the followmg December. 
No damage was detected to any plants growing in the quadrats; all 
developed, matured, and died on the treated as well as on the control 
- quadrats. In March 1933, following the winter rains, or 1 year 
after the distribution of thalgrain on the quadrats, the composition 
and the density of vegetative growth was redetermined for each 
quadrat and compared with the original values. 
TABLE 2.—Fffect of thallous sulphate upon density of vegetative growth 
Vegetative den- Vegetative den- 
7 sity Nae | atta, sity Shera 
-_| Thallous cover ar allous cover 
Quadrat no. cheer Sulphate! 28 oes Es |e Quadratino: See ea Sulphate ||esic ees ee beers 
Pp per acre | Pp *~ | per acre 
Origi- | After 1 Origi- | After 1 
nal year | nal year 
Pounds | Pounds Pounds | Pownds 
j a ee OS 0 0 10.0 TSO ia eee ee oe 3. 000 50 8.0 0.3 
2eE ee 1, 000 10 7.0 SHON Gee we oes ae 7, 500 75 8.5 a8; 
SORE Eten: , 000 20 6.0 PaAV || Paranal eet 10, 000 100 8.5 pall 
EI oR a 3, 000 30 7.0 aia ase eee ea ae 20, 000 200 7.0 Aik 
| 
These quadrat experiments show that very high concentrations of 
thalgrain, when left on the surface of the ground throughout a year 
cause inhibiting effects on growth of vegetation. A marked decrease 
in plant growth was observed following the application of 3,000 
pounds or more of thalgrain per acre. Some decrease in vegetative 
growth was observable when 20 to 30 pounds of thallous sulphate 
per acre were applied, corresponding to 2,000 to 3,000 pounds of thal- 
erain per acre. In interpreting these figures it must be remembered 
that in control work the maximum application of thalgrain in the 
original treatment is only 1 pound per acre, but that this is applied 
to so limited a portion of the entire surface that it would correspond 
to approximately 1,000 pounds of thalgrain per acre if the entire 
area were covered. This quantity caused a slight stimulation in 
vegetative growth on the treated quadrat. It must also be remem- 
bered that thalgrain is distributed only when the animals to be con- 
trolled will take it rapidly. Usually nine-tenths of the baits are eaten 
