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 Sprayer Calibration and the Tree
Row Volume Method
Foliar pesticide spray applications in tree fruit
orchards are made almost exclusively with airblast
sprayers. Thenumber and frequency of sprays needed
each season represents nearly 20% of seasonal production
costs. All aspects of the spraying operation need to be as
cost-efficient as possible. Just because a treatment
provides good pest control does not mean that it is also
efficient. One reason for this inefficiency is that
conventional guidelines for pesticide recommendations
lack precision, and are frequently misunderstood. In this
section we offer guidelines for defining spray volume and
concentration requirements, and for sprayer calibrations to
obtain maximum performance and consistent control.
Tree Row Volume (TRV) and
Determining Pesticide Dosage
The required dosage of any pesticide is the amount
that must be applied per unit of target area that achieves
the desired level of pest control. Determining when a
pesticide dosage is too low is relatively easy since more
pest damage is seen. It is more difficult to tell when the
dosage level exceeds the required amount because there is
often little or no difference in the level of pest damage.
Using too little or too much pesticide is costly.
Excessive rates mean increased costs, excessive worker
exposure, unnecessary environmental contamination, and
disruption of integrated control programs. Pesticide
dosage is determined by two factors: 1) the concentration
of the pesticide in the spray tank (pounds of product per
target unit (gallons per acre).
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100 gallons of water) and 2) the spray volume applied per
Target Definition. Defining the target area as "an acre"
is too variable, and may lead to either too much or too
little pesticide being applied. House painters determine
the amount of paint required for a job by defining the
house in more relevant terms. Thus, painting
recommendations are never stated on a gallons-per-house
basis, but on a gallons-per-1,000-square-foot basis. Fruit
growers face a similar problem in determining how much
pesticide is needed to treat an acre of orchard. The
amount of target area within an orchard acre varies with
tree size, planting density, and the degree of canopy
development.
The "conventional acre" is a two-dimensional unit of
area (43,560 square feet) and is accurate for pesticide
dosage in orchards only when applying herbicide sprays
to ground areas. For tree spraying, the "orchard acre"
needs to be redefined in terms that are relevant to a three-
dimensional target. This is done by using tree row
volume (TRV) to estimate the volume of the target to be
treated. Here, adjustments can be made for differences
among orchards in tree size and planting density. TRV
per acre is calculated by multiplying tree height (H) x
foliar canopy width (W) x the row length (L) per acre,
therefore:
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H x W x L = cubic feet TRV per acre
The row length per acre (L) above is determined by
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dividing 43,560 square feet per acre by the distance
between rows in feet as shown below.
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