. Control of field rodents on California farms. Rodents. the gas several days later to those that have been reopened by squirrels. Others consider that this method takes too much time except on clean-up work. Burrows under trees should be treated only by use of the rodent gun and the gas ignited a few seconds later so none of it remains. Waste balls dripping with carbon disulfide may produce a concen- tration of the chemical that will injure or kill a tree by absorption through the roots. Some earlier vapor pumps required numerous strokes, but forced carbon disulfide vapor more or less through
. Control of field rodents on California farms. Rodents. the gas several days later to those that have been reopened by squirrels. Others consider that this method takes too much time except on clean-up work. Burrows under trees should be treated only by use of the rodent gun and the gas ignited a few seconds later so none of it remains. Waste balls dripping with carbon disulfide may produce a concen- tration of the chemical that will injure or kill a tree by absorption through the roots. Some earlier vapor pumps required numerous strokes, but forced carbon disulfide vapor more or less throughout the burrow; the Demon Rodent Gun re- quires only a single stroke, but tends to leave varying amounts of the liquid close to where the nozzle was inserted and does not force the vapor so far down the bur- row. Sulfur dioxide gas. Sulfur burned in the presence of air generates sulfur dioxide. Machines to produce and force this gas into squirrel burrows have been built and used by California farmers. One has used a gasoline torch with a sul- fur chamber in front of the flame; the draft created by the torch forces the fumes through a nozzle inserted in the burrow. Another type is a cylindrical tank through which air is forced by a hand-driven rotary blower over the burn- ing sulfur; fumes from the sulfur pass into a large hose inserted in the squirrel burrow. The whitish fumes, besides killing squirrels below ground, will reveal leaks from cracks in the ground surface or from other entrances connected with the same tunnel system. Then the operator can shovel earth to close the leaks. Some users of sulfur dioxide report good re- sults, but others believe that this gas is not effective enough. Other gases. Calcium cyanide, in flake or dust form, placed in or pumped into a damp burrow, generates hydro- cyanic acid (HCN), a deadly gas rapidly fatal to all forms of animal life. Many years ago, calcium cyanide was tried by official agencies for ground-squirrel con- trol in California
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