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A
typical spray system applies a single herbicide rate over
an entire area of the field.
This approach generally provides effective weed control,
but with some applications, a significant herbicide waste
may occur. The reason for this is because weeds are not
evenly distributed over an entire field, but occur sporadically.
Selective spraying involves spraying only a portion of the
field where weeds are present. This approach may result
in a significant reduction in herbicide use and save on
input costs.
This
is not a new approach. Spot spraying is a type
of selective spraying, but involves manually directing the
spray towards the weed(s). Automatic devices that sense
the presence of weeds have been available for a number of
years.
From
1974 to 1998,
one can find numerous studies on automated systems. Hanks
et al. (1998) found an average herbicide saving of 78% in
cotton and 51% in soybean over a two year study. Griffin
et al. (1998) reported Roundup savings of 29 to 68% and
5 to 27% in different experiments.
These systems use differences in spectral characteristics
between living plant material and soil. Plant detection
is achieved by sensors measuring red and near-infrared reflectance
from plants, crop residues, and soil. Plants strongly absorb
red wavelengths and reflect near-infrared wavelengths.
Once plants (weeds) are detected, a solenoid/nozzle assembly
is signaled to spray. Applications have been used not only
in agronomic crop land, but in vineyards, orchards, roadsides,
and military and industrial use as well.
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This
project will examine the utility of using a light-activated
sprayer on the Texas Southern High Plains.
An economic analysis will be done comparing weed control
from conventional systems compared to weed control using
a light-activated spray system.
After
one year of research,
we found that this sprayer controlled weeds similar
to conventional spray applications.
Yield
from plots treated with the light-activated sprayer were
also similar to plots treated with conventional applications.
Herbicide savings during three applications ranged from
56 to 85%. Unfortunately, even with these savings, it would
be hard to justify purchasing this equipment at this time.
If an 8 row unit costs $38,000 and herbicide savings are
65 and 80%, it will take about 6 years to pay for this equipment.
Research
will continue in 2001 in cotton and peanut to evaluate the
effectiveness and feasibility of using a light-activated
sprayer to control weeds in west Texas.
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