Agriculture Reference
In-Depth Information
After atomization, droplets must travel to the target and be deposited uniformly
on the target so that the biochemical mechanisms have the high probability of effec-
tively controlling the pest of interest. Uniform deposition is dependent on nonvary-
ing factors such as the nozzle spacing and the type and characteristics of nozzles
installed on the sprayer. It is also dependent on factors that vary in the field including
nozzle distance from plant canopy, nozzle pressure, ambient temperature, humidity,
and wind speed and direction.
10.2.3 L
IMITED
O
FF
-T
ARGET
A
PPLICATION
OR
D
RIFT
Another important performance requirement, which is related to uniform deposi-
tion, is that deposition occurs on the target to which the chemical is intended to be
applied. Movement of the chemical to off-target locations is called drift, and it is a
major problem with chemical application systems. Grover et al. (1997) performed
in-field trials to quantify the extent of spray drift for typical row crop applications.
Drift was defined as the percentage of the applied volume drifting beyond the boom
edge of a boom sprayer for a single sprayed swath. For an extended range flat fan
nozzle (Teejet XR 11002, Spraying Systems, Wheaton, IL) at low wind speeds (7.7
km/h measured perpendicular to the sprayer's travel path), 8.23% of the applied vol-
ume drifted beyond the boom edge. Increased wind speed (14.9 km/h) with the same
nozzle increased drift to 12.7%. High wind speed (28 km/h) resulted in 35.6% of the
applied volume drifting beyond the edge of the boom. The result of this off-target
deposition is damage to nontarget organisms, environmental concerns, as well as
reduced target application rates. Drift losses in orchard spraying with an air-blast
sprayer can be between 8% and 45% for typical applications (Planas and Pons, 1991;
Siegfried and Raisigl, 1989; Pergher et al., 1996).
As shown within the Grover study, spray drift is directly related to wind speed.
Nuyttens et al. (2007) found that the drift distance of a droplet—and thus the result-
ing magnitude of drift distance for an application—is highly correlated to canopy
distance from the droplet release point, droplet size, nozzle pressure, temperature,
and humidity. Droplet size has been found to be the overall most significant factor
affecting the magnitude of drift (SDTF, 1997). Very fine droplets (those less than
150 microns) reach terminal velocities nearly instantaneously after release, causing
them to become suspended in the air and thus highly displaceable because of cross
winds. Best management practices to reduce spray drift include spraying with large
diameter droplets, low canopy distance, and under low wind speed conditions.
10.2.4 H
EALTH
AND
S
AFETY
OF
O
PERATORS
Another important performance requirement is that the health and safety of chemi-
cal applicators be protected from exposure to the chemicals being applied for pest
control. The main means of accomplishing this requirement is to reduce off-target
drift and to separate the operator from the environment where accidental exposure
could occur. Applicators contact pesticides both during the addition to and mixing of
the active ingredient of the pesticide with the carrier volume and during the applica-
tion itself. A study by Cruwin et al. (2002) found that only 75% of farmers wear any
