Orchard Math
101:
For Proper Spray
Application
1. Calculate GPA (gallons per acre) for the
specific orchard.
Begin with Tree Row Volume (TRV). Refer to diagram on page 3.
TRV = Tree
diameter (ft) x Tree height (ft) x 43,560
Row
spacing (ft)
Use TRV to determine Gallons per Acre (GPA). A dilute constant* should be selected: 0.5 for bare trees, 0.7 for sparse trees
(minimum), or 1.0 for dense canopies (maximum).
GPA = TRV
x (dilute constant*)
1,000 cu ft
Proper GPA should give good coverage without over-dosing
or under-dosing. Refer to page 3 for
recommended adjustments.
2. Select appropriate nozzles to deliver proper
gallonage.
Convert GPA to Gallons per Minute (GPM). Note:
For tractors without a speedometer, MPH calculation on page 3.
GPM = GPA
x MPH x Row spacing (ft)
495
GPM is the total gallonage needed. Now, divide by the number of nozzles.
GPM per Nozzle = _____GPM_____
Number of nozzles
Choose individual nozzles based on the GPM per
Nozzle. Know pump PSI (have a
gauge). Hollow cone nozzles are
recommended for canopy sprays (airblast).
Hollow cone nozzles produce appropriate size droplets for canopy
applications. Flat fan nozzles are used
for herbicides. Ceramic nozzles are most
resistant to abrasion and corrosion.
They are worth the extra cost.
See example Tee Jet
selection guide below.
Check coverage and drift.
Calibrate sprayer. Refer to recommended adjustments section below.
Check coverage, deposition, and drift. Some recommendations include:
ü
Deposition should penetrate tree canopy but not
blow through to the next row.
ü
Monitor deposition with water sensitive paper or
photo paper, attach to poles in the center of tree row, stapled upward every 12
inches. Also, use water sensitive paper
in next row to monitor blow through and drift.
ü
Droplet size should be fine, but not aerosol. If droplets are too big (>300µm), they
will bounce from leaf surfaces. If
droplets are too small (<150 µm) they will drift without sticking. Hollow core nozzles produce droplets within
ideal range.
ü
Droplets density (droplets per cm2)
should range from 20-30 droplets per cm2 for insecticides and 50-70
droplets per cm2 for fungicides.
There should not be streaks or overlapping spots. Refer to label. Sample data sheet from water sensitive paper
attached (page 4-7).
ü
Adjust nozzle direction for best coverage. Monitor by using poles with flagging (air
direction) for even coverage. 70% of
spray should cover the top half of the canopy.
30% of the spray should reach the lower half of the canopy.
ü
Calibrate sprayers annually by 1) confirming
tractor speed (MPH), 2) calculating nozzle output (see page 1), and 3) checking
nozzle outputs (see book Effective Orchard Spraying). Error up to ±5%, adjust pump pressure or
tractor speed. Error over ±10%, replace
nozzles.
ü
Most orchard pumps are too large for modern
canopy architecture. Ideal pressure is
below 150 psi, but centrifugal pumps range from 150 to 200psi. Diaphragm pumps have a wider range of
adjustment, but they are more expensive.
It is critical to have a gauge to measure psi. Lower pressure by
adjusting fan blade pitch, adjusting fan speed via PTO or separate pump. Keep pressure as low as possible; high
pressure creates horseshoe vortex and boundary layer.
ü
Adjust air volume via reducing intake (wooden
donut) or reducing outlet (louvers) to eliminate blow through.
ü
Run a constant speed; faster travel speed causes
turbulence.
ü
Calibrate nozzles and check for wear. Change nozzles if ±10%. Clean tank and nozzles often.
ü
Miles per hour (MPH) can be calculated by
marking a 100 ft row, using a stopwatch to time the drive run, and then
calculating MPH = ___100
ft row x 60__
Seconds traveled x 88
Example: from
Syngenta website
Water-Sensitive Paper
What is
water-sensitive paper?
Water-sensitive paper is a rigid paper with a
specially coated, yellow surface which will be stained dark blue by
aqueous droplets impinging on it. It has been developed for field use by
Syngenta for the quick evaluation of LV sprays. For droplet assessment,
aqueous sprays no longer need the addition of dye. Just place the papers
in the target area before spraying. Following exposure to the spray the
water-sensitive papers will be stained. Retrieve the papers as soon as
they have become dry. Check the droplet pattern. For a quick estimate
compare the exposed collectors with a known standard or count the
droplets either using a hand lens or an automatic image analyzer.
Water-sensitive paper
after exposure. (Courtesy Spraying Systems Co.)
Where to use it
Water-sensitive paper can be used for checking
spray distribution, droplet density from aerial and ground spray
applications and droplet sizing.
Overdosing is a waste of product. With herbicides,
it might result in crop damage and claims. With insecticides underdosing
might not kill the pest. Calibrate the sprayer and check the spray
pattern. Water-sensitive paper helps you to keep the environment clean.
Airblast sprayers in
orchards: staple water-sensitive paper directly onto leaves at the periphery
and inside the canopy at the top, in the center and lower part of the
trees.
Number the collectors consecutively before
placing them on the supports. This will help you to spot irregularities in
your spray system when evaluating the exposed cards.
The correct boom height can also be determined
with water-sensitive paper. Insufficient overlapping of the spray pattern
can be corrected by raising the boom. Excessive overlapping is leveled out
by lowering the boom.
Visual assessment of
droplet densities
Compare your spray samples with some known
standard. The standard cards below and on the following page cover the
range of acceptable droplet densities for coarse and medium LV spray. The
droplet density in the target area should not be less than:
For routine checking of sprays you might also
prepare your own standard cards by selecting spray cards with known
droplet densities from previous spray operations.
Standard cards with a
known droplet density per cm square
Computer-plotted standard cards displaying the
expected number and sizes cards spraying at 3 different volume rates (20,
30, 40 l/ha) and using 3 different droplet spectra (VMD, 200, 300)
assuming waters sprayed and the spread factor is two.
This handout was produced for the
Kentucky Extension IPM Implementation Program,
Fruit Crops Working Group
By
Nicole Gauthier, Extension Plant Pathologist and Ric Bessin, Extension
Entomologist.