ERADICATING THE COMMON BARBERRY 41 
determined only by trial. Second, it is difficult to obtain locally 
in quantity and at short notice. To obtain a sufficient quantity to 
treat several hundreds or perhaps thousands of barberries would 
necessitate waiting until enough accumulated in the mains. Third, 
the odor of drip oil is very persistent and will remain for many 
months about the spot to which the oil is applied. 
WATER-GAS TAR 
Water-gas tar is a heavy residue in the manufacture of water gas. 
It was obtained locally at 5 cents a gallon. No greenhouse tests were 
made, but there were a number of field trials. 
An application of 0.8 gallon of water-gas tar was made to each of 
12 standing barberry bushes on October 1, 1921. In July, 1923, only 
3 of these bushes were dead. An application of 0.7 of a gallon was 
made to each of 18 barberries on the same date. These bushes pre- 
viously had been cut down. All were alive in July, 1923. 
Water-gas tar is a black, viscid, ill-smelling liquid that is very 
disagreeable to handle. It scarcely penetrates the ground but cakes 
and remains on the surface. The shoots and roots of the barberries 
that were touched by the chemical were killed, but the lateral roots 
were healthy outside the area to which the tar was applied, and 
many sprouts arose from them. It would seem that these roots are 
capable of sprouting to some extent even if undisturbed when the 
crown of the bush is killed, unless the killing agent is a chemical 
which penetrates the roots. 
The results of these tests with water-gas tar do not justify anr 
further experiments with this substance. 
SUMMARY OF CHEMICALS STUDIED 
In the foregoing pages the results obtained by treating barberry 
plants with each of 37 different chemicals are reported. It is pos- 
sible that some of the other chemicals might be satisfactory if the 
best method of application was determined by more extensive study. 
This is illustrated by experiments with kerosene, which proved in- 
effective in the greenhouse trials yet were very satisfactory in the 
field. This is further shown in experiments with a concentrated 
sodium-arsenite solution and crystals of sodium dichromate which 
were ineffective, while dilute solutions of both proved effective kill- 
ing agents. Time was a very important item, as hundreds of thou- 
sands of dollars were being spent annually in barberry eradication, 
much of which was being wasted by ineffective methods. A delay 
of a year in reaching a practical solution of the problem of suc- 
cessful eradication would have resulted in a very considerable loss. 
Therefore, efforts were concentrated on those chemicals which gave 
the most promise in the earlier studies. 
Although the results are fragmentary and incomplete, they throw 
some light on what may be expected of different types of chemicals 
when used to kill barberries or other plants. The character and dis- 
tribution of the roots in the soil are all important in the case of 
plants that sprout readily from the crown and roots and therefore are 
not easily killed by sprays or by other methods that merely kill the 
tops. To kill such plants with a chemical, it is necessary to apply 
