ERADICATING THE COMMON BARBERRY 31 
iactory chemical for eradicating barberries must be effective in vari- 
ous types of soil and under various weather conditions. It did not 
appear worth while to make a more critical study of the factors 
favoring the action of carbon bisidphide. 
One other fact should be mentioned. Of all the chemicals tried 
in the wood lot near Gurnee, 111., carbon bisulphide did the most 
damage to the trees near the treatments. One large cherry tree and 
two oaks were killed. These trees had trunks from 6 to 10 inches in 
diameter and were 8 to 10 feet from the treated barberry plants. 
PARADICHLOROBENZENE 
Paradichlorobenzene (C 6 H 4 C1 2 ) is a white crystalline substance. 
It is used to a considerable extent as a substitute for naphthalene 
and other moth repellents. It also has been successfully used for 
killing peach-tree borers. Blakeslee (1) and others have reported 
that, when it is used to kill borers in the crown of the tree, injury 
or death of the tree is likely to result when a large dose is used. 
As the dosage for killing borers is 1 ounce or less to the tree, it 
seemed probable that this substance in larger quantities might be 
an efficient herbicide. Guyton and Stear (5) suggest designating 
paradichlorobenzene as PDB. 
In the greenhouse in experiments with barberries in 8-inch pots 
a dose of 5.2 grams per pot caused discoloration and dropping of 
the leaves, but the roots apparently were healthy one month after the 
treatment. An application of 1.25 grams dissolved in 20 cubic 
centimeters of kerosene and applied to a plant killed the tops of 
the plant, but two months after the application the roots were still 
healthy in appearance. 
In the field, treatments were made on two different dates at Mar- 
shall, Wis. On December 10, 1921, 10 barberries were treated with 
one-fourth of a pound each. Half of the bushes were cut down and 
the others were left standing. The chemical was placed in a trench 
5 inches deep and close to the crowns of the bushes. No injury to 
the plants was noted the following year, and on July 27, 1923, they 
apparently were healthy. . 
The second treatment was made on April 20, 1922, when 18 bushes 
were treated with 1 pound each. Here also half had been pre- 
viously cut down. The chemical was placed in a trench 3 inches 
deep close to the crown and covered with earth. No apparent injury 
resulted to any of these bushes. 
SODIUM CYANIDE 
Sodium cyanide (NaCN) in the form of crystals was applied to 
the soil in 8-irich pots of barberries. Death of the plants was caused 
in eight days by 5.2 grams sprinkled on the surface of the soil. 
Although this was a very satisfactory showing, the cost of the chem- 
ical was such that no field tests were made. Calcium cyanide was 
tried in the field, however. 
AMMONIUM PICRATE 
Ammonium picrate (C 6 H 2 (N0 2 )30NH 4 ) in crystal form was ap- 
plied to potted barberries growing in the greenhouse. Applications 
of 5.2 grams to the surface of the soil in an 8-inch pot failed to 
