Agriculture Reference
In-Depth Information
A prepared dust is a finely ground, dry mixture consisting of a low con-
centration of active ingredient (usually 1% to 10% by weight) combined with
an inert carrier. Because dust particles are finely ground, they may drift long
distances from the treated area even when wind velocities are low. Herbicides
are not formulated as dusts principally because of this potential for drift.
Dusts present a significant inhalation hazard to the applicator and leave a visi-
ble residue on plants. They are of limited importance in ornamental and turf
pest control.
Despite their ease in handling, formulation, and application, dusts are the
least effective and, ultimately, the least economical of the pesticide formula-
tions. The reason is that dusts have a very poor rate of deposit on foliage,
unless it is wet from dew or rain. In agriculture, for instance, an aerial appli-
cation of a standard dust formulation of pesticide will result in 10 percent to
40 percent of the material reaching the crop. The remainder drifts upward and
downwind.
12. Granules
Granules are very much like dusts except that the inert particles are much
larger. Granules are normally made by applying a liquid formulation of the
active ingredient (ranging from 2% to 40% by weight) to particles of clay or
other porous materials such as corn cobs or walnut shells.
Following application, the active ingredient is released gradually from the
inert material. Granules are generally less susceptible to degradation and
leaching than other soil-applied formulations. Because granules are relatively
large, they drift less than most other formulations and there is little inhalation
hazard. However, it is often difficult to accurately calibrate granular spreaders
and to obtain uniform distribution of the granules.
Granular formulations are used almost exclusively as soil treatments.
They may be applied either directly to the soil or over the plants; they do not
cling to plant foliage. They may be used to control pests living at or below
ground level or they may be absorbed by roots and translocated throughout the
plant. The latter are, for the most part, either systemic insecticides or sys-
temic herbicides.
Only insecticides and a few herbicides are formulated as granules. They
range from 2 to 25 percent active ingredient and are used almost exclusively in
agriculture, although systemic insecticides as granules can be purchased for
lawn and ornamentals. Granular materials may be applied at virtually any
time of day, since they can be applied aerially in winds up to 20 mph without
problems of drift, an impossible task with sprays or dusts. They also lend
themselves to soil application in the drill at planting time to protect roots
