Evaluation of Low-volume Sprayers Used in
Asian Citrus Psyllid Control Applications
Clint Hoffmann1,8, Brad Fritz1, Dan Martin1, Ryan Atwood2,
Tim Hurner3, Mark Ledebuhr4, Matt Tandy5, John L. Jackson6,
and Gail Wisler7
ADDITIONAL INDEX WORDS. technology, Diaphorina citri, greening
SUMMARY. The asian citrus psyllid [Diaphorina citri (Sternorrhyncha: Psyllidae)] is
a detrimental pest to citrus (Citrus spp.) crops when it serves as a vector of the
pathogen that causes greening (huanglongbing). Transmission of this disease causes
mottling, chlorosis, dieback, and reductions in fruit size and quality. Citrus
producers have found that many pesticides, when applied properly, are very
effective at suppressing or eliminating asian citrus psyllids in groves. Due to the
threat of greening, several pesticides have been granted Special Local Needs
registration for use in the state of Florida if the product is sprayed with a volume median
diameter of 90 mm or greater. A number of studies involving numerous citrus sprayers
and a.i. were conducted to determine the droplet sizes generated by different
sprayers operating under user-established settings and the adjustments required
to those settings for the sprayers to meet the 90-mm requirement. In the sprayer
tests, it was found that reductions in engine speed or increases in flow rate were
required to increase droplet sizes to meet the product label-required droplet size.
As the equipment tested here represent the most typical application equipment
used in Florida for asian citrus psyllid control, these results will provide applicators,
growers, and extension agents with general guidelines to ensure that spray
systems are operated in a manner that complies with label restrictions.
T
he asian citrus psyllid is a detrimental pest to citrus crops
when it serves as a vector of
the pathogen that causes greening
[huanglongbing (HLB)]. Transmission of this disease causes mottling,
chlorosis, dieback, and reductions in
Mention of a trademark, vendor, or proprietary
product does not constitute a guarantee or warranty
of the product by the U.S. Department of Agriculture
or U.S. Navy and does not imply its approval to the
exclusion of other products that may also be suitable.
This study was supported in part by a grant from the
Deployed War-Fighter Protection (DWFP) Research
Program, funded by the U.S. Department of Defense
through the Armed Forces Pest Management Board
(AFPMB).
1
U.S. Department of Agriculture-Agricultural Research Service-Areawide Pest Management Research
Unit-Aerial Application Group, 2771 F&B Road,
College Station, TX 77845
2
University of Florida, IFAS Extension, 1951 Woodlea Road, Tavares, FL 32778
fruit size and quality (Halbert and
Manjunath, 2004). Once a tree is
infected, there is no cure, and trees
may only live for another 5 to 8 years,
potentially never bearing usable fruit.
It is well established that the presence
of asian citrus psyllids and the vectored pathogen necessitate chemical
control in the form of pesticide applications (Tolley, 1990). Given the
seriousness of the disease, it is important to protect even apparently
disease-free trees (Aubert, 1990),
especially with new growth flush
(Aubert 1987). Recommended treatment intervals range from 10 to
13 treatments per year (Roistacher,
1996) to every 7 to 20 d (Gonzales
and Viñas, 1981), with area-wide
treatments being preferred (Aubert
1990). Supriyanto and Whittle (1991)
recommend high-efficacy pesticides
as essential to provide sufficient control to significantly delay a greening
epidemic. It can be further conjectured that optimal application techniques also are critical to obtaining
maximum biological control of asian
citrus psyllids.
Stover et al. (2002), in a survey
to indentify current spray application
practices on citrus crops in Florida,
identified three predominate sprayer
types, including two airblast sprayers
at mid- and high-volume application
rates and a low-volume application
rate air-assisted sprayer, with spray
rates ranging from 25 to 750 gal/
acre. Sprayer type is generally selected
by the operator based on experience
and/or perceived coverage and deposition of spray material within the
citrus canopy. The selected sprayers
can typically be modified to generate
spray plumes that fit tree contours
through changes in nozzle numbers,
and orientation of and/or oscillation
of airflow (Stover et al., 2003). With
the need for numerous spray treatments for asian citrus psyllid control,
applicators are looking to and adapting for use a number of spray application machines initially targeted for
the mosquito vector control industry.
Machines that apply agrochemical
products at these low-volume rates
allow applicators to respond to the
need to treat large numbers of acres
repeatedly in a timely manner. These
machines can produce droplets with
volume median diameters that range
from 5 to 210 mm, depending on
spray solution and equipment setup
(Hoffmann et al., 2007a).
The list of pesticides approved
for application to control asian citrus
psyllids in Florida is limited. As a result
of the urgent need for control, applicators in Florida have been granted
Special Local Needs provisions on
a number of insecticides, including
spinetoram (DelegateÒ WG; Dow
3
University of Florida, IFAS Extension, 4509 George
Boulevard, Sebring, FL 33872
4
Ledebuhr Industries, 795 Progress Court, Williamston, MI 48895
5
Curtis DynaFog, 17335 U.S. Highway 31 North,
Westfield, IN 46074
6
Florida Citrus Industry Research Coordinating
Council, 30205 SR 19, Tavares, FL 32778
7
U.S. Department of Agriculture-Agricultural Research Service, National Programs, 5601 Sunnyside
Avenue, Beltsville, MD 20705
8
Corresponding author. E-mail: clint.hoffmann@ars.
usda.gov.
632
Units
To convert U.S. to SI,
multiply by
U.S. unit
SI unit
To convert SI to U.S.,
multiply by
0.3048
3.7854
9.3540
2.54
1
0.4470
70.0532
6.8948
ft
gal
gal/acre
inch(es)
micron
mph
oz/acre
psi
m
L
Lha–1
cm
mm
ms–1
gha–1
kPa
3.2808
0.2642
0.1069
0.3937
1
2.2369
0.0143
0.1450
•
June 2010 20(3)
AgroSciences, Indianapolis), diflubenzuron (MicromiteÒ 80WGS; Chemtura, Middlebury, CT), fenpropathrin
(Danitol 2.4 EC; Valent, Walnut
Creek, CA), and zeta-cypermethrin
(Mustang; FMC, Philadelphia). All
of these Special Local Needs labels
require air-blast or air-assisted sprayers
with application rates of no less than
2 gal/acre and with volume median
droplet diameters of 90 mm or larger.
Most labels allow the addition of
adjuvants or other tank-mix partners
as long as the other restrictions are
maintained; however, fenpropathrin
does not allow use of additional adjuvants. No information is given regarding the reasoning behind the
90-mm lower limit, though it is likely
based on risk assessment analysis for
spray drift. The Special Local Needs
labels also do not specify an upper
limit on the droplet size. Given that
spray droplet size is dependent on and
changes with varying combinations
of spray equipment, equipment setup,
and spray product (Hoffmann et al.,
2007b), the objectives of this work
were: 1) evaluate three sprayers, under laboratory conditions, for droplet
size produced from a.i. formulations
and the necessary equipment adjustments needed to meet the Special
Local Needs label; 2) conduct ‘‘onsite’’ evaluations of production application equipment for droplet size
when operating under normal conditions; 3) adjust the individual sprayer’s
operating parameters to produce a volume median diameter of 90 mm or
greater to ensure compliance with the
Special Local Needs labels; and 4)
document the general operational
modifications required for machine
type to provide guidance for future
spray calibrations.
field-based evaluations were conducted at two locations in central
Florida. Both sets of trials followed
the same testing protocols with the
exception of the field-based trials not
using a.i. formulations. These procedures, along with greater details on the
site-specific testing, are discussed further in the following sections.
GENERAL TESTING PROCEDURES.
To evaluate the droplet size produced
by a particular sprayer and spray formulation combination, the sprayer
was first operated under its normal
factory or user-established settings.
Basically, the sprayer was initially operated as-is. A droplet measurement
system (Sympatec, Clausthal, Germany) mounted on a custom-made
forklift mount was used to measure
droplet size at the sprayer nozzle
outlet. The unit was positioned such
that the location of measurement was
1 to 2 m from the outlet of the
sprayer (Fig. 1). This distance varied
somewhat from sprayer to sprayer
depending on the droplet density of
the resulting spray cloud and the
width of the spray plume. Wider spray
plumes required a closer distance to
avoid depositing spray material on the
lenses of the droplet measurement
unit. Denser sprays required further
distance to insure that the spray cloud
density did not prevent the diffracted
laser light from reaching the measurement sensor. The spray cloud from
the sprayer was directed through the
laser beam for 10 to 20 s during
which time droplet size measurements of the spray cloud were made.
The time that the spray cloud was
directed through the optical path of
the laser varied between sprayers
depending on the width of the spray
plume generated by the sprayer. The
entire spray plume for each sprayer
was measured by traversing the laser
through the plume using the forklift
(ASTM International, 2009). Three
replicated measures were made for
each unique piece of equipment and
specific set of operational conditions.
DROPLET SIZING SYSTEM. The
Helos laser diffraction droplet sizing
system (Sympatec), which uses a 623nm helium-neon laser, was fitted with
an R5 lens, resulting in a dynamic size
range from 0.5 to 875 mm in 32 sizing
bins. The authors found that when
using the laser system under adverse
conditions (outdoors and mounted
to a forklift), the last channel (i.e.,
sizing bins) of the Helos system
should be turned off such that it is
not factored into the droplet size
measurement results. This channel
represents the largest droplet size
and tends to pick up some ‘‘noise’’
or random signals that typically result
from equipment vibration or scattered ambient light. With this channel
turned off, the dynamic range of the
instrument was from 0.5 to 735 mm.
These channels were not turned off if
any droplets were measured within
two sizing bins of the nearest deactivated channel.
The spray droplet size data were
determined and reported as a mean
and standard deviation corresponding to the data measured during the
three replications for each combination of sprayer and pesticide. Means
and standard deviations of the volume
median diameter [VMD or DV0.5
(ASTM International E1620-97,
2004)], DV0.1, and DV0.9 were determined. The DV0.5 is the droplet
diameter in micrometers where 50%
of the spray volume is contained in
droplets smaller than this value (ASTM
Materials and methods
Sprayer droplet size testing was
completed in two stages: one looking
at three sprayers and five a.i. under
laboratory conditions and the second,
a field-based evaluation of production
sprayers brought to a central location
by local applicators. The first laboratory-based work was conducted at
the U.S. Department of AgricultureAgricultural Research Service (USDAARS) Areawide Pest Management
Research Unit’s Riverside campus facilities in College Station, TX. The three
sprayers to be evaluated were provided
by the equipment manufacturers. The
•
June 2010 20(3)
Fig. 1. Testing setup showing the droplet measurement system with the spray
plume from the citrus sprayer directed through the laser beam of the droplet
measurement system.
633
TECHNOLOGY AND PRODUCT REPORTS
Standard E1620, 2004). Similarly,
the DV0.1 and DV0.9 values are the
diameters at which 10% and 90%,
respectively, of the spray volume is
contained in droplets of these sizes.
ACTIVE INGREDIENT TESTS. For
the laboratory studies, five a.i. along
with water plus a nonionic surfactant
(NIS) were used. The use of a specially
designed scrubbing system allowed
for the use of these a.i. without adverse environmental impacts. Three
liquid-based products were used:
malathion (Malathion 5EC; Drexel
Chemical, Memphis, TN), dimethoate (Dimethoate 4E; Arysta LifeScience North America, Cary, NC),
and fenpropathrin. Two of the products were wettable powders: diflubenzuron and spinetoram. The rates at
which these products were tested are
shown in Table 1. For all a.i. tests,
spray rates were maintained at 3 gal/
acre. For each of the three sprayers
tested, the first step was to run the
sprayer at the factory settings using
water to determine a benchmark for
further modifications. Depending on
the measured DV0.5, engine speed was
modified such that the 90-mm lower
size requirement was met. The goal
for each a.i. formulation tested was to
determine the appropriate engine
speed settings that resulted in compliance with the Special Local Needs
permit.
C ITRUS SPRAYER CALIBRATION
RODEOS. The field evaluations were
organized by the Florida Extension
Service in Lake Placid, FL, and Haines
City, FL. Growers and applicators in
the region were invited to bring their
equipment to these locations for droplet size measurements. Thirty-three
machines were evaluated representing
Table 1. Five a.i. (three liquid and
two wettable powders) and the rates
at which they were used in the
sprayer calibration trials.
Liquid
formulation
Malathion
Dimethoate
Fenpropathrin
Wettable
powders
Diflubenzuron
Spinetoram
z
1 oz/acre = 70.0532 gha–1.
634
Application rate
(oz/acre a.i.)z
9.0
13.9
6.2
Application rate
(oz/acre a.i.)
5.0
1.0
16 different models of sprayers. Water
with 0.25% volume/volume addition
of a NIS (R-11; Wilbur-Ellis, Walnut
Creek, CA) was used during these
tests as there were a large number of
spray trials conducted and a large
number of people involved. This prevented any environmental contamination or adverse health effects. The
water plus NIS solution simulates
most water-based insecticide sprays
well (Hoffmann et al., 2007a,
2007b). Each sprayer tested was initially run at the user settings. Based
on the measured DV0.5, engine
speed and, in a few cases, sprayer
pressure were adjusted until the 90mm size requirement was met. Typically, engine speed was first reduced
to its minimum level and if the
resulting measured DV0.5 was still
less than 90 mm, spray pressure was
increased.
An example of the data reports
that were provided to each of the
applicators is shown in the Appendix
(Fig. 2).
Results
ACTIVE
INGREDIENT TESTS WITH
THREE SPRAYERS. Final equipment set-
tings required to meet the DV0.5 90mm size requirement for each a.i. are
shown in Tables 2 through 4 for the
three sprayers tested. Droplet size at
the factory settings for water and
water plus NIS are also included for
reference. For the London Fog model
18–20 sprayer (London Fog, Long
Lake, MN) (Table 2), initial testing
with water and water plus NIS with
the machine operating at 2810 and
1850 rpm, respectively, and a rate of
1.9 Lmin–1 produced DV0.5 of 57.8 ±
13.2 and 85.9 ± 1.2 mm (mean ± SD of
three replications), respectively. Two
of the a.i. formulations, diflubenzuron and spinetoram, produced
DV0.5 values that were at or near the
90-mm requirement while operating
the sprayer at 1500 rpm while two,
fenpropathrin and malathion, required reducing the engine speed to
1350 rpm. The dimethoate formulation was such that even at the lowest
engine speed setting (1350 rpm), the
90-mm size requirement could not
be met.
For the Curtec sprayer (Curtec
of Florida, Vero Beach, FL), water
and water plus NIS resulted in DV0.5
that were greater than 90 mm at
factory settings. Dimethoate and
diflubenzuron formulation also achieve
the 90-mm requirement at the factory
settings, while the malathion, spinetoram, and fenpropathrin formulation required engine speeds to be
reduced to 4800, 4000, and 4000
rpm, respectively.
For the Proptec sprayer (Ledebuhr
Industries, Williamston, MI), water
and water plus NIS resulted in DV0.5
values that met the 90-mm requirement. Spinetoram and diflubenzuron
formulations also met the 90-mm
requirement at the 5100-rpm factory setting, while malathion and
fenpropathrin formulations required
the engine speed to be reduced to
3500 rpm.
C ITRUS SPRAYER CALIBRATION
RODEOS: SINGLE MACHINE
EVALUATIONS. During the calibration
rodeos, there were 17 unique models
of machines evaluated. Fourteen of
the models only had one machine of
that type that was tested. Two, the
Dyna-Fog Ag-Mister LV-8 (Curtis
Dyna-Fog, Westfield, IN) and the
London Fog model 18–20, had multiple machines of that type tested.
Of the individual machines
tested, eight had a DV0.5 of 90 um
or greater (Table 5). Three of the
remaining sprayers were able to be
adjusted via spray pressure or engine
speed to achieve a DV0.5 near or
greater than 90 mm. One of the
sprayers, MaxCharge ES100 (Electrostatic Spraying Systems, Watkinsville, GA), was designed to generate
droplets with a DV0.5 of between 30
and 40 mm to optimize the electrostatic charge that it imparts to the
spray droplets.
There were 14 Dyna-Fog AgMister LV-8 (LV-8) and six London
Fog model 18–20 citrus sprayers evaluated in the calibration rodeos (Table 6). Each row of data presented
in Table 6 represents a unique machine. These machines were all of
different age, levels of maintenance,
degree of user modification, and standard operating settings thus variation
in spray droplet size among the machine was expected. Of the 14 LV-8
sprayers, four were version 1 (LV-8V1), one was version 2 (LV-8-V2),
and nine sprayers contained some
modifications of pumps and spray
lines that made it difficult to distinguish a specific version. Therefore, all
data are presented by individual machine, with no attempt to characterize
•
June 2010 20(3)
Table 2. Effects of a.i. and engine speed on spray atomization for the London Fog model 18–20 sprayer (London Fog, Long
Lake, MN).
Formulation
Water
Water + 0.25% NISx
Diflubenzuron
Spinetoram
Fenpropathrin
Malathion
Dimethoate
Engine speed
(rpm)
Rate per
atomizer
(gal/min)z
DV0.1 y
(mm ± SD)
Droplet sizey
DV0.5
(mm ± SD)
2810
1850
1500
1500
1350
1350
1350
0.6
0.6
0.6
0.6
0.6
0.6
0.6
22.3 ± 5.1
30.2 ± 2.3
38.1 ± 0.4
35.1 ± 0.5
38.1 ± 0.7
37.1 ± 1.0
30.0 ± 2.7
57.8 ± 13.2
85.9 ± 1.2
94.0 ± 2.7
86.4 ± 0.6
91.4 ± 0.4
92.0 ± 0.9
79.6 ± 2.8
DV0.9
(mm ± SD)
110.6 ± 22.3
214.7 ± 14.8
305.5 ± 6.5
260.7 ± 12.9
322.2 ± 10.5
279.2 ± 9.9
205.1 ± 52.7
z
1 gal = 3.7854 L.
DV.01, DV.05, and DV.09 = the droplet diameter where 10%, 50%, and 90%, respectively, of the spray volume is contained in droplets smaller than this value. Values represent the
mean of three replications; 1 mm = 1 micron.
x
NIS = nonionic surfactant (R-11; Wilbur-Ellis, Walnut Creek, CA).
y
Table 3. Effects of a.i. and engine speed on spray atomization for the Curtec sprayer (Curtec of Florida, Vero Beach, FL).
Formulation
Water
Water + 0.25% NISx
Dimethoate
Malathion
Spinetoram
Diflubenzuron
Fenpropathrin
Engine speed
(rpm)
Rate per
atomizer
(gal/min)z
DV0.1
(mm ± SD)
Droplet sizey
DV0.5
(mm ± SD)
DV0.9
(mm ± SD)
5100
5100
5100
4800
4000
5100
4000
0.3
0.3
0.3
0.3
0.3
0.3
0.3
41.3 ± 9.4
35.3 ± 5.2
37.9 ± 5.9
31.2 ± 1.3
66.0 ± 23.1
39.9 ± 3.7
44.3 ± 1.7
111.8 ± 12.8
94.9 ± 4.6
96.7 ± 11.0
88.9 ± 0.6
126.4 ± 11.9
105.2 ± 6.4
113.2 ± 2.9
173.6 ± 17.9
149.1 ± 4.2
167.3 ± 11.5
168.7 ± 9.0
200.5 ± 13.1
185.5 ± 11.4
218.6 ± 33.5
z
1 gal = 3.7854 L.
DV.01, DV.05, and DV.09 = the droplet diameter where 10%, 50%, and 90%, respectively, of the spray volume is contained in droplets smaller than this value. Values represent the
mean of three replications; 1 mm = 1 micron.
x
NIS = nonionic surfactant (R-11; Wilbur-Ellis, Walnut Creek, CA).
y
Table 4. Effects of a.i. and engine speed on spray atomization for the Proptec sprayer (Ledebuhr Industries, Williamston,
MI).
Formulation
Water
Water + 0.25% NISx
Malathion
Spinetoram
Diflubenzuron
Fenpropathrin
Engine speed
(rpm)
Rate per
atomizer
(gal/min)z
DV0.1
(mm ± SD)
Droplet sizey
DV0.5
(mm ± SD)
5100
5100
3500
5100
5100
3500
0.36
0.36
0.36
0.36
0.36
0.36
29.4 ± 0.8
33.0 ± 4.2
33.7 ± 1.6
32.6 ± 2.0
31.6 ± 1.1
34.5 ± 0.4
98.4 ± 5.7
94.9 ± 15.8
91.6 ± 4.0
97.6 ± 5.9
93.8 ± 3.8
96.4 ± 2.1
DV0.9
(mm ± SD)
161.2 ± 13.6
193.0 ± 21.6
173.6 ± 3.8
165.8 ± 7.0
172.9 ± 4.1
209.5 ± 11.1
z
1 gal = 3.7854 L.
DV.01, DV.05, and DV.09= the droplet diameter where 10%, 50%, and 90%, respectively, of the spray volume is contained in droplets smaller than this value. Values represent the
mean of three replications; 1 mm = 1 micron.
x
NIS = nonionic surfactant (R-11; Wilbur-Ellis, Walnut Creek, CA).
y
general sprayer model performance.
For each machine tested, the droplet
size under the initial operational settings is presented followed by the
droplet size at the adjusted settings.
Typically, for the LV-8 and LV-8-V2,
decreasing the engine rpm resulted in
increased droplet size such the 90-mm
size requirement was met. There were
•
June 2010 20(3)
several of the LV-8 machines that,
even with maximum reduction of
the engine speed, the 90-mm level
was not met. Each of the individual
machines tested had unique lower
engine speed, again due to variability in machine age, maintenance,
and level of modification. For the
LV-8-V1 machines tested, similar
adjustments in engine speed did not
result in sufficient increase in droplet
size. The LV-8-V1 has a smaller
pump and small diameter tubing leading to each of the spray nozzles,
which limits flow output and thereby
the ability to generate larger droplets.
The London Fog model 18–20
citrus sprayers followed similar trends
635
TECHNOLOGY AND PRODUCT REPORTS
Table 5. Spray droplet size measurements from sprayers in the citrus spray calibration rodeo with the original setting results
followed by the adjusted setting results for a water plus nonionic surfactant solution. The sprayers were adjusted to comply
with the droplet size requirements of the Special Local Needs permits granted to some insecticides in the State of Florida.
Original settings
Liquid
Air
pressure pressure
(psi)y
(psi)
Sprayerz
Model no.
Nozzlez
Spray
rate
(gal/acre)y
Adapco
AirTec
Curtec
Curtec
Curtec
Curtec
London
Fog
ESS
190GS
CAB1000
648 D
648 D
C3000
P400D
2D MaxiPro
Standard
Albuz
Curtec coarse
Curtec fine
Curtec coarse
Proptec coarse
Standard
2
25
10
10
21
2
2
15
2
1 gal/miny
4
2800
540 - PTOw
2100
1500
540 - PTO
2100
2500
MaxCharge
ESS100
Standard
15
20
30
440 - PTO
3
7
1700
3
5
5
10
8
1700
2500
450 - PTO
1700
Proptec
Proptec
Rears
Rears
Sides
PulBlast
PulBlast
Spectrum
Proptec
coarse
Proptec fine
Rotary
Albuz ATR-80
Ogee shear
3
70
50
150
42
Adjusted settings
Air
Liquid
pressure pressure
(psi)
(psi)
Engine
speed
(rpm)
Engine
speed
(rpm)
Sprayer
Model no.
Nozzle
Targeted
rate
(gal/acre)
Adapco
Curtec
Curtec
London
Fog
ESS
190GS
648 D
C3000
2D MaxiPro
Standard
Curtec coarse
Curtec coarse
Standard
2
10
21
2
0
3
15
1 gal/min
0
4
1900
1500
440 - PTO
1640
MaxCharge
ESS100
Standard
15
30
25
540 - PTO
5
0
7
1300
5
0
7
1300
Proptec
Proptec
Proptec
coarse
Proptec fine
Droplet size in first testx
DV0.1
DV0.5
DV0.9
(mm ± SD)
(mm ± SD)
(mm ± SD)
17.2 ± 1.5 51.1 ± 5.8
37.3 ± 0.3
99 ± 1.2
30.4 ± 0.4 75.5 ± 0.8
31.6 ± 1.0 87.1 ± 3.7
27 ± 0.4 70.9 ± 0.6
63.2 ± 4.8 149.2 ± 12.2
121.4 ± 13.8
173.7 ± 4.5
133.8 ± 2.3
159.7 ± 17.6
130.6 ± 4.2
335.8 ± 79.7
17.6 ± 0.2
38.4 ± 0.1
79.4 ± 6.2
14.3 ± 0.3
41.9 ± 0.3
102.9 ± 1.1
31.5 ± 1.8 75.5 ± 6.7
31.6 ± 0.4 80.7 ± 4.2
131.6 ± 8.3 278.9 ± 16.9
56.4 ± 0.8 131.4 ± 0.4
38.6 ± 2.3 99.7 ± 8.2
147.3 ± 28.1
139.3 ± 4.5
390.7 ± 25.7
214.9 ± 1.0
184.8 ± 27.4
Droplet size after adjusting sprayerx
DV0.1
DV0.5
DV0.9
(mm ± SD)
(mm ± SD)
(mm ± SD)
39.2 ± 1.1
31.9 ± 0.8
33.3 ± 2.1
107.6 ± 4.5
79.1 ± 1.8
95.7 ± 2.7
227.2 ± 14.8
142.1 ± 4.5
180.2 ± 1.0
29.4 ± 2.1
76.7 ± 5.6
177 ± 11.5
13.3 ± 0.5
34.7 ± 1.4
83.9 ± 3.0
31.3 ± 1.8
37.4 ± 2.0
75.5 ± 6.7
88.7 ± 3.6
147.3 ± 28.1
162.9 ± 13.1
z
Adapco (Sanford, FL); AirTec (AirTec Sprayers, Winter Haven, FL); Curtec (Curtec of Florida, Vero Beach, FL); London Fog (Long Lake, MN); ESS (Electrostatic Spraying
Systems, Watkinsville, GA); Proptec (Ledebuhr Industries, Williamston, MI); Rears (Rears Manufacturing, Eugene, OR); Sides (Goldthwaite, TX); Albuz (Spirit River, AB,
Canada); Ogee (Spectrum Electrostatic Sprayers, Houston).
y
1 gal/acre = 9.3540 Lha–1, 1 psi = 6.8948 kPa, 1 gal = 3.7854 L.
x
DV.01, DV.05, and DV.09= the droplet diameter where 10%, 50%, and 90%, respectively, of the spray volume is contained in droplets smaller than this value. Values represent the
mean of three replications; 1 mm = 1 micron.
w
Power take-off.
as the LV-8s. With a single exception,
reducing the engine speed increased
DV0.5 values such that the 90-mm size
requirement was met.
Conclusions
In response to the need for accurate droplet size assessments of
application equipment used in the
control of the asian citrus psyllid in
Florida, a variety of field application
sprayers were evaluated to determine
if the applied sprays met the Special
Local Needs labeling requirements of
volume median diameters of 90 mm
or greater. Initially, a series of studies
was conducted across three typical
636
spray systems and five a.i. to determine typical machine operating characteristics and resulting droplet sizes.
From these tests, it was found that for
typical air-blast type sprayers, reductions in engine speed were required to
reduce air-shear atomization to increase droplet sizes to the required
size. For air-assisted sprayers, this also
held true with the addition that increased flow rate also potentially increased droplet size. Following these
initial assessments, a series of droplet
sizing rodeos were held in Florida
to measure spray droplet size from
applicator- and grower-owned citrus sprayers operating in ‘‘as-is’’
conditions. Based on the resulting
spray droplet size, the sprayer settings
were adjusted such that the resulting
droplet size would comply with the
label requirements. Following the
trends seen in the initial round of
testing, the majority of the sprayers
was adjusted via the engine speed or
spray pressure such that the resulting
spray’s volume median diameter was
greater than or equal to 90 mm. As the
equipment tested here represent the
most typical application equipment
used in Florida for asian citrus psyllid control, these results will provide
applicators, growers, and extension
agents with general guidelines to
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June 2010 20(3)
3
5
3.5
2.5
3
2.4
3
3
3
2
3
1
2
5
0.4
1
2
1.8
1.8
3
LV8
LV8
LV8
LV8
LV8
LV8
LV8
LV8
LV8
LV8-V1
LV8-V1
LV8-V1
LV8-V1
LV8-V2
18–20
18–20
18–20
18–20
18–20
18–20
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
Dyna-Fog
London Fog
London Fog
London Fog
London Fog
London Fog
London Fog
4
7
6
6
10
8
7
9
9
9
6
7
6
7
7
7
2260
2500
2500
2600
2600
2600
2600
2600
2140
2600
1670
2600
2600
2500
2600
2850
2720
2600
2600
2500
Engine speed
(rpm)
23.6 ± 3.9
21.1 ± 2.7
16.1 ± 1.6
15.8 ± 0.9
20.4 ± 0.6
22.4 ± 0.1
24.8 ± 0.4
26.5 ± 2.1
24.4 ± 0.7
14.6 ± 0.8
18.3 ± 0.7
13.2 ± 1.8
14.2 ± 0.8
27.2 ± 1.6
12.4 ± 0.6
18.9 ± 0.1
22.8 ± 0.7
31.6 ± 1.6
32.2 ± 2.6
24.9 ± 5.6
64.5 ± 11.9
55.5 ± 6.4
47.1 ± 3.3
39.6 ± 2.1
53.1 ± 2.7
64.1 ± 2.1
76 ± 4.7
76.8 ± 4.4
69.8 ± 2.3
50.1 ± 12.7
44.2 ± 2.1
35.3 ± 1.7
35.4 ± 1.9
76.7 ± 1.5
25.9 ± 2.0
46.8 ± 0.1
62.0 ± 0.1
83.1 ± 3.7
89.9 ± 4.0
65.1 ± 17.7
Original settings
Droplet sizex
DV0.5
DV0.1
(mm ± SD)
(mm ± SD)
130.6 ± 23.9
112.9 ± 11.4
101.7 ± 3.5
79.8 ± 7
106.3 ± 10.3
131.5 ± 16.5
185.4 ± 0.1
176.3 ± 19.2
160.9 ± 8.3
157.9 ± 31.3
90 ± 1.4
69.2 ± 4.3
70.9 ± 5.3
166.7 ± 21.4
57.1 ± 18.4
85.0 ± 0.3
130.6 ± 3.5
177.9 ± 13.9
190.2 ± 4.4
134.7 ± 23.8
DV0.9
(mm ± SD)
2260
1800
1350
2100
1800
2040
1400
2120
2000
1600
1350
2300
2000
2020
1900
1800
1800
2400
2400
1500
29.7 ± 1.1
27.3 ± 0.3
33.5 ± 1.1
28.6 ± 0.6
34.1 ± 0.9
37.3 ± 2.3
42.2 ± 1.7
35.2 ± 0.7
31.1 ± 0.1
21.5 ± 0.4
22.1 ± 1.6
17.5 ± 0.5
17.2 ± 0.4
33.1 ± 2.6
24.1 ± 1.1
37.0 ± 0.4
48.1 ± 0.8
35.8 ± 2.3
30.2 ± 0.6
49.1 ± 1.9
87.8 ± 0.9
71.8 ± 0.4
95.5 ± 6.9
73.3 ± 2.9
98.9 ± 4.8
113.7 ± 11.9
123.8 ± 13.9
107.2 ± 4.0
98.8 ± 2.7
55.6 ± 0.5
56.1 ± 3.8
44.8 ± 0.2
45.7 ± 1.9
97.3 ± 1.8
61.1 ± 2.5
90.3 ± 1.9
117.9 ± 0.1
96.1 ± 3.1
93.2 ± 3.4
124.4 ± 6.1
Results after adjusting sprayer
Droplet sizex
DV0.1
DV0.5
Engine speed
(mm ± SD)
(mm ± SD)
(rpm)
219.5 ± 19.7
151.4 ± 1.2
240.1 ± 11.1
154.8 ± 2.8
197.3 ± 24.9
239.5 ± 33.7
277.3 ± 62.7
226.8 ± 11.0
242.3 ± 38.9
117.4 ± 2.4
112.2 ± 12.8
88.1 ± 2.5
93.5 ± 7.6
234.2 ± 16.0
104.2 ± 4.5
167.0 ± 9.6
237.8 ± 4.0
202.4 ± 15.8
221.6 ± 26.7
246.5 ± 7.6
DV0.9
(mm ± SD)
LV8 and LV8-V2 have 3/8- to 1/2-inch tubing to each nozzle, LV8-V1 has 1/8-inch tubing to each nozzle; 1 inch = 2.54 cm.
y
1 gal/acre = 9.3540 Lha–1; 1 psi = 6.8948 kPa.
x
DV.01, DV.05, and DV.09= the droplet diameter where 10%, 50%, and 90%, respectively, of the spray volume is contained in droplets smaller than this value. Values represent the mean of three replications; 1 mm = 1 micron.
z
Spray rate
(gal/acre)y
Model
no.z
Sprayer
Air
pressure
(psi)y
Table 6. Spray droplet size measurements for Curtis Dyna-Fog LV8 (Curtis Dyna-Fog, Westfield, IN) and London Fog model 18–20 (London Fog, Long Lake, MN)
sprayers in the citrus spray calibration rodeo with original setting results followed by the adjusted setting results for a water plus nonionic surfactant solution. The sprayers
were adjusted to comply with the droplet size requirements of the Special Local Needs permits granted to some insecticides in the State of Florida.
insure that spray systems are operated
in a manner that complies with label
restrictions.
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Appendix
Fig. 2. Handout given to applicators at the citrus sprayer calibration rodeos to explain the results of the tests;
1 mm = 1 micron, 1 gal = 3.7854 L, 1 psi = 6.8948 kPa, 1 m/s = 1 mS21 = 2.2369 mph.
638
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