Another chemical found to be even more effective as a larvicide is
powdered borax. This substance is available in commercial form in all
parts of the country. It has the advantage of being comparatively
nonpoisonous and noninflammable and is easily transported and handled.
The minimum amount necessary to kill fly larvæ was found to be 0.62
pound per 8 bushels of manure, or about 1 pound per 16 cubic feet. Best
results were obtained when the borax was applied in solution, or when
water was sprinkled on after the borax had been scattered evenly over
the pile. Borax is not only effective in killing the larvæ, but when it
comes in contact with the eggs it prevents them from hatching. When
applied at the rate of 1 pound to 16 cubic feet it was found to kill
about 90 per cent of the larvæ, heavier applications killing from 98 to
99 per cent.
Borax has no injurious effect on the chemical composition or rotting of
the manure. However, when added in large quantities with manure to the
soil it will cause considerable injury to growing plants. A number of
experiments have been conducted to determine the effect on crops of the
use of manure treated with borax as herein recommended. When applied at
the rate of 15 tons per acre it appears that no injury as a rule will
follow. Some crops are more sensitive to borax than others, and also the
tendency to injury appears to vary on different soils. It is necessary,
therefore, to repeat the warning issued in connection with a previous
bulletin[11] on this subject, that great care be exercised, in the
application of borax, that the manure does not receive more than 1 pound
for every 16 cubic feet, and that not more than 15 tons of manure so
treated are applied to the acre.
In view of the possible injury from the borax treatment as a result of
carelessness in applying it, or from other unforeseen conditions, it is
recommended that horse manure and other farmyard manures which are to be
used as fertilizer be treated with hellebore. Borax, on the other hand,
is such a good larvicide that it call be used with advantage on the
ground of soil-floor stables, in privies, on refuse piles, and on any
accumulations of fermenting organic matter which are not to be used for
fertilizing purposes.
[Footnote 11: Department Bulletin 118, U. S. Department of Agriculture,
p. 25.]