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Future Orchard Walk November 2014
Spraying apples
David Manktelow freshLearn Ltd email: [email protected]
Summary
Effective and efficient spray application is a critical part of apple production. Spray liquid and sprayer air outputs need to be matched to different tree targets, in order to deliver an effective chemical dose with sufficient target coverage. Timely and economic spraying is a trade-‐off between travel speeds and spray volumes to maximise spraying work rates without compromising target penetration and coverage.
Setting up sprayers to maximise on-‐target deposition will help reduce spray losses as drift. However, sprayer operators have to be able to time and manage spraying operations to minimise drift to sensitive areas.
Calibration and maintenance checks are an essential part of setting up sprayers – calibration sets and confirms travel speeds, spray volume output distributions to different tree targets, operating pressures and spray droplet sizes. Regular in-‐season checks by the operator on filters, agitation, nozzles etc. are needed to maintain and optimise sprayer performance.
Unfortunately spraying is something of a black art, with feedback on poor application coming by way of control failures – and usually much too late to identify and fix potential problems. Simple in-‐season checks on sprayer coverage are recommended to help identify coverage issues and to match sprayers to different target canopies.
Despite the large number of variables and decisions that need to be made, spraying is simple. There are four basic rules to sprayer setup and spray optimisation:
1) Direct the spray output towards the target canopy – the number one problem with spraying is a failure to hit the target. Park the sprayer in a block to be treated and work out which nozzles should be turned on and what proportion of the output is directed to different tree zones. Aim to direct two thirds of the output volume into the top half of single leader trees and into the top third of multi-‐leader trees.
2) Adjust your chemical application rate to match different target canopies. To achieve the same chemical dose per square centimetre of tissue, large canopies and/or close row spacings need higher application rates than smaller canopies and/or wider row spacings. A simple row-‐length based sprayer calibration system can be used to make these adjustments.
3) Penetrate the target by matching air output volumes to travel speed to canopy density and wind conditions. You are spraying the row you are in – try and get the spray plume to project about 1m above and beyond the target canopy on the upwind adjacent row. If it doesn’t either increase air outputs, increase spray volumes, or slow down. If spray is projecting too far either speed up, or reduce air output.
4) Dose without coverage will not provide control – make sure you achieve sufficient coverage for the chemical mode of action and the pest or disease target. Simple coverage-‐monitoring tools include water sensitive papers or tracers such as UV dyes or kaolin clay. Water sensitive papers on fixed targets provide a cost effective and fast way to improve and confirm sprayer performance.
Sprayer Types
Airblast sprayers
Airblast sprayers are the most common general fruit crop sprayer around the world. They are well suited to reliably and cost effectively spraying orchards with a range of canopy sizes and row spacings. Airblast sprayers use an axial fan to generate a large volume of relatively low velocity air. Air is typically drawn into the fan from the rear of the sprayer and turned to generate a radiating plume at an angle of about 15o into the direction of travel. Most fans rotate counter clockwise (viewed from behind) and penetration performance is weakest on the right hand side – sprayers can often be seen to fail to penetrate into a crosswind in the tops of trees on the right hand side.
Some airblast sprayers are fitted with straightening vanes to compensate for the uneven air outputs caused by fan rotation. These are reasonably effective, but traditional vanes require approximately 20% more horsepower (and diesel) to run and increase sprayer noise outputs.
Recent improvements in fan technology with fibre reinforced moulded fan blades have achieved significant improvements in air output evenness and volumes from axial fan sprayers.
A good rule of thumb for axial fans is that they can produce approximately 1,000 m3 of air per horsepower input to the fan. Airblast sprayers in modern apple canopies should be producing between 30-‐60,000 m3 per hour – typically with an air velocity at the nozzles of around 60-‐90 km/hr.
Figure 1: Two modern axial fan air blast sprayers
Air shear sprayers
Air shear spray units use high velocity air (typically
>300 km/hr) to shatter a bleed of spray liquid into fine droplets. It takes significant input power to produce air at these speeds and most air shear sprayers
produce lower air volumes than axial fan sprayers and are more adversely affected by wind and excessive travel speeds.
An important limitation of air shear sprayers is that
the air available is optimised to atomise relatively low volumes of spray liquid – they perform best as concentrate sprayers usually at 3X-‐5X less than runoff
volumes for typical apple canopies. As spray liquid feed rates to nozzles increases the droplet sizes and size range increases and the nozzles start to “spit”. It
is possible to use air shear sprayers to apply high volume sprays to the point of runoff, but they are best used as dedicated low volume sprayers.
Air shear sprayers are simple and reliable, but need to
be operated within the limitations imposed by their available air outputs.
Figure 2: Air shear tower sprayer in apples
Tower and multi-‐row sprayers
Tower sprayers aim to move spray and air delivery vertically up the canopy wall to allow more accurate
targeting of specific canopy areas. Many variations of tower sprayers have been produced and used in apples around the world, usually with claims (often
unjustified) for drift reduction and coverage improvements.
There are airshear, airblast and directed fan versions of tower sprayers on the market. All have different
strengths and weaknesses, but the process for setting up and optimising tower sprayer performance is essentially the same as that for axial fan sprayers.
Two and three row sprayers are starting to be used in
intensively planted apple canopies – typically up to 3.8m tall on 3.5m row spacings. Multi-‐row sprayers usually feature airbags or stacks of directed fans.
Multi-‐row sprayers offer high spraying workrates (hectares treated per hour), but they rely on well laid out blocks of consistent trees. They represent a
significant capital investment and growers considering adopting multi-‐row spraying technology need to plan for backup spraying options in the event of
breakdowns.
Figure 3: Quantum Mist directed axial fan tower sprayer. Note the different head orientations on each side, with the overlapped
outputs on LHS upwards oriented heads giving the
best coverage.
Nozzles and droplet sizes
Nozzles: Most sprayers (except air shear and spinning
disc sprayers) uses high pressures (6 to 25 bar) through small orifice cone nozzles (e.g.: disc-‐core, hollow cone or full cone types) to ideally produce
“fine” (~100-‐150 μm diameter [see footnote and
Figure 4]) spray droplets. Fine droplets rely on sprayer air assistance to carry them to the canopy, but
they can provide excellent coverage on leaves and fruit. In practice most high volume dilute or 2X concentrate spraying on orchards has a wide range of
droplet sizes from “very fine” to “coarse”. The smaller the droplet size, the greater the risk of spray drift, the larger the droplet size the more patchy and
one sided the resulting spray coverage.
Rules of thumb with nozzles; 1) Hollow cone nozzles produce smaller droplet
sizes and a smaller droplet size range than solid cone nozzles.
2) Wide angle nozzles produce smaller droplet sizes than narrow angle nozzles.
3) Lower output nozzles produce smaller droplet
sizes than higher output nozzles – it is usually better to divide outputs between two low output nozzles than to rely on one higher output nozzle.
4) Smaller droplet sizes and wider angle nozzles
are more reliant on sprayer air assistance than jetty high output nozzles.
When spraying in windy conditions or near sensitive areas, larger droplets (>250 μm) are preferred to
reduce the risk of off-‐target drift. Air induction (AI) nozzles, which produce large spray droplets (typically 300-‐ 600μm), can help minimise drift losses in high
risk situations. The use of large droplet sprays is starting to be mandated on some chemical labels to reduce drift risks.
AI nozzles produce droplets containing small air
bubbles, which reduces the mass of the droplets and assists with coverage (compared to droplets of the same size produced by other nozzles). Despite the
advantages of AI nozzles for reducing drift risks, the increase of spray droplet size will almost always compromise spray retention and coverage (compared
to application of finer droplets).
11 μm = microns and is the usual unit for measurement of droplet diameters. 1mm = 1000 μm. Droplet sizes produced by different nozzles are usually described in terms of the VMD or volume medium diameter. At a quoted VMD half of the spray volume from a particular nozzle is contained in droplets with diameters less than the VMD and half is contained in droplets with diameters greater than the VMD.
Figure 4: Classification scheme for nozzles used in agricultural spraying in accordance with
(ASABE) s572 (American society of agricultural and biological engineers).
Managing and tuning sprayer air assistance
Too much air and/or too great an air velocity tends to reduce deposits on canopy close to the sprayer as spray is blown off the target. Conversely, most of the spray volume projected beyond the canopy in the rows adjacent to the sprayer will be lost to the ground in the inter-‐row space (large droplets fall out, fine droplets drift, but don’t account for much spray volume). An important part of optimising airblast sprayer performance is to match air assistance to the canopy being treated.
You are aiming to replace the air within a canopy with spray laden air. Larger/denser canopies will require more air than smaller/more open canopies. In practical terms this means that you can travel faster in small/open canopies on narrow row spacings than you can in large/dense canopies on wider row spacings.
In all cases it is important to set the sprayer to target just the row that you are in – maximum deposits and coverage will be achieved when you see the spray plume reach at least a meter beyond and above trees in the upwind adjacent row.
Sprayer calibration
There are two distinct parts to sprayer calibration. The first part is the planning phase. This involves decisions on spray application volumes, travel speeds, nozzle types, droplet size, nozzle output arrangement, use of air, and air speed and profile. This part of
calibration is often done in the winter by independent specialists. The second part of calibration is the checking and tuning phase. In most spraying operations the spray nozzles are already fitted, and travel speeds, output volumes and chemical rates have been established. At this stage the operator needs to ensure that the target is adequately covered, to watch for leaks and blocked or damaged nozzles, to check filters and tank agitation and to confirm that application volumes match those expected. If the area or row length to be treated is known, it is possible to estimate how much can be treated per tank and how many tanks will be required to treat the area. Operators need to check these expected figures against the actual volumes used and look to fix any application problems as they occur. This is a very important on-‐going calibration check, it is best done by the operator and effectively requires no calculations. Acceptable errors in calibration and application
A well calibrated sprayer should deliver a chemical volume that is within 5% of that targeted and any differences of more than 10% should be fixed.
For example, a sprayer calibrated to deliver 1,000 L/ha should consistently deliver 950 to 1,050 L/ha and should not go beyond 900 to 1,100 L/ha.
Spray volumes and chemical rates Chemical application rate recommendations are often made in terms of product rates per hectare. This is fine for broad acre boom spraying. However, is not sensible for tree crops where different row spacings and canopies can represent very different spraying targets per hectare.
Chemical labels in Europe prescribe chemical rates per hectare and tree fruit growers have trouble making adjustments on the basis of tree size.
Chemical labels in Australia and New Zealand prescribe a mixing concentration of chemical per 100 litres of dilute spray. This should make it easy to adjust application volumes, and hence chemical application rates, to match the size and density of different target canopies. In practice there is still a lot of confusion as to how best to define chemical application rate requirements for different canopies.
Row-‐length calibration
A method for distance-‐based calibration was developed in Australia, initially for use with wine grapes. This method replaces application volumes per
hectare with application volumes per 100 metres of row. Under this system canopies of different sizes, or at different stages of seasonal development, are
assigned different application volume targets (i.e. different delivery volumes per 100 metres of row length). Once this is done, it becomes very easy to
calibrate sprayers using simple tables in place of the normal calibration formulas and calculations.
The current SprayWise recommendations for apple canopies are that 20-‐25 litres of spray volume will be
required per 100 metres of canopy row per metre of tree height for fungicides and 25-‐30 litres per 100 metres for miticides and PGRs
(www.croplands.com.au).
Canopy volume or Tree-‐Row-‐Volume (TRV) calibration
TRV spraying is similar to row length calibration. It
was developed on American apples over 40 years ago and has since been proven in NZ apples. The base assumption of TRV spraying in apples is that one litre
of dilute spray can wet (cover) something between 11
and 14 cubic metres of canopy volume to the point of runoff – with the 11 m3/l figure relating to dense
canopies and 14 m3/l relating to more open canopies. For very dense canopies, or where the spray target requires full wetting (e.g. scale insects with mineral oil
sprays and some thinning sprays) a greater application volume will be required, and a coverage factor of between 7.5 to 11 m3/l may be required.
It is easy to estimate TRV for a block by measuring; 1) Height of crown, 2) average canopy spread and 3) row spacing (Figure 5).
Figure 5: Simple TRV measurement
Calculating Tree-‐Row-‐Volume
TRV (m3/ha) =
Height (m) x Spread (m) x 10,000 ÷ Row spacing (m)
Example: If crown height = 3.5 m, spread is 2.6 m and
row spacing is 4.5 m.
TRV = 3.5 x 2.6 x 10000 ÷ 4.5
= 20,222 m3/ha (or around 20,000 m3/ha)
Estimating required application volumes
Dilute spray volume (l/ha)
= TRV (m3/ha) ÷ Coverage factor (m3/litre of spray)
Example: If TRV = 20,000 m3/ha and the coverage factors selected are 14 m3/litre spray for fungicides
and 11 m3/litre for thinning sprays.
Dilute spray volume required for fungicides = 20,000 ÷ 14 = 1,428 l/ha (round to 1,500 l/ha) Dilute spray volume required for thinners = 20,000 ÷ 11 = 1.818 l/ha (round to 1,800 l/ha) In practice it is sensible to establish three or four TRV groupings for different canopies on your property, each with a similar spray volume requirement. You
should then work out how best to achieve the different application volumes for the different blocks (by turning off nozzles, by varying travel speed etc.).
Deposit variability Well setup sprayers on regular canopies in full leaf can
deposit as much as 90% of the output spray volume on the target canopy. Spray deposition efficiency in the early season is much lower, with dormant
canopies only capturing 5-‐10% of the applied spray volume.
Spray deposits through trees will always be variable. When dilute spraying to the point of runoff, outer,
easily sprayed, canopy zones typically receive 2X higher deposits than lower inner canopy zones and 3X higher deposits than upper inner canopy zones.
Similar variability is seen with low volume concentrate sprays, but a lack of runoff in outer canopy zones often results in 5-‐fold variations in deposits through
trees.
The lack of runoff losses from concentrate sprays at 3X or greater results in average deposits that are 10-‐15% higher than those achieved from dilute spraying.
The deposit variability patterns above relate to
average deposits in different zones of trees. Deposit variations on individual fruit and leaf surfaces can be significantly higher. However, in most cases chemical
efficacy is achieved because there is some chemical movement from the point of initial deposition.
Despite being able to live with significant deposit variability, spray coverage visualization is an
important tool to help identify application problems and to improve sprayer performance.
Dilute versus Concentrate spraying Chemical labels for tree crops in New Zealand and
Australia prescribe a tank mixing concentration of chemical per 100 litres of spray mix. This concentration is expected to control the target pest or
disease when the spray is applied “dilute to the point of runoff”.
The point of runoff is quite subjective, but it assumes that target surfaces are sufficiently covered with spray
to retain a high enough chemical dose to achieve control. In most canopies, when spray begins to drip from the outer exposed canopy (the point of runoff),
the inner canopy will have received approximately half to a third of the dose of the outer canopy.
A majority of chemical labels make provision for
sprays to be applied using volumes below the point of runoff. Water is just a dilutent and carrier for the chemical, and modern adjuvant technology can
actually improve coverage and retention of low volume sprays. Low volume spraying can greatly reduce the down time of repeated tank fills.
However, there is definitely some safety in volume and most low volume spraying in apples is undertaken at a half, a third or a quarter of the runoff volume.
It is important that the chemical application rates that
would be used in a dilute spray application are maintained. If half of the runoff spray volume is used, the chemical mixing concentration should be doubled
(2X concentrate). If the spray volume is reduced to a quarter of the runoff volume, the tank mixing concentration should be increased by a factor of four
(4X concentrate) etc.
Spray coverage estimation using water sensitive papers to optimise sprayer performance
Water sensitive papers are yellow sheets of card
(usually 75mm X 25mm) that turn blue on contact with water. They are an excellent indicator of spray coverage and also provide a lot of information on
spray droplet sizes.
Papers go grey on exposure to high humidity and are easily marked by fingerprints. They need to be kept in a sealed packet in a dry place. When handling the
papers it is usually best to wear latex gloves, although they can be used without gloves provided you are careful to just touch the edges or backs of the cards
(Figures 6a, b, c).
Figure 6a: Handling water sensitive papers. Take 10 papers, turn one to face the others to reduce finger prints
Figure 6b: Fold in half and gently pull the inner paper out from the stack
Figure 6c: Clip papers onto horizontal and vertical holders (the wire clips shown work well but bull dog clips are ok)
For coverage testing in any crop it is best to place the papers in areas where poor coverage is suspected to occur. In apples we have found the use of a fixed
target spray pole located approximately half a metre along the row from a tree trunk will provide a good indication of inner canopy spray deposits.
Usually 10 folded papers (giving 20 coverage surfaces)
are all that is needed to identify patterns in spray coverage and differences in sprayer performance.
Examples of the sort of coverage you can expect to see are shown in Figures 7 and 8.
Figure 7:1600 l/ha to standard 4.5m tall Royal Gala trees in December.
Note: Runoff in lower papers and lighter coverage in tree tops (second paper from the top). A little more of
the output should have been directed into the tree tops, but these papers show excellent coverage.
Figure 8: Application of 450 l/ha (dilute) for fruitlet thinning to just the tops of dwarf (4m tall) Royal
Gala trees using just the top nozzles on the sprayer.
Note: Good coverage in the tops, but not to the point of runoff.
There is not much point putting papers in the outer canopy as most coverage problems occur in the inner
and upper canopy zones. Spraying is best done using water, although it can also be done when the sprayer is being used in a chemical spray round.
Retrieve the papers as soon as possible after spraying and keep some notes that describe the sprayer setup
and application volume, the target canopy and the weather conditions at the time of spraying. Either staple or glue (a glue stick is good) the recovered
papers to this notes sheet (see template at the end of these notes).
Making a judgment on coverage performance
Placing all of the papers systematically onto a record sheet allows you to make an overall assessment of
spray coverage. Look for both poor coverage and excessive runoff (too much spray volume for the target requirements).
It is useful to score the number of paper surfaces out
of the total that have inadequate coverage. Experience in wine grape spraying suggests that pest and disease control is likely to be compromised in
canopies where 20% or more of papers placed around bunches show poor coverage.
Improving spray coverage
Each coverage test with water sensitive papers should take only about ten minutes. If you are unhappy with the spray coverage achieved try and identify the most
likely limiting factor and test whether an adjustment to this improves coverage. It is best to make only one adjustment at a time and then retest, as that way you
can identify what factors have the greatest effect on your spray coverage. Factors that you might consider testing to improve fruit coverage include:
• travel speed – usually you may need to slow down in big dense trees, but with large fans in small trees speeding up can improve coverage.
• sprayer air output -‐ change fan gear, fan pitch or PTO speed to adjust air outputs
• droplet size – increase pressure to get finer
droplets or change to fine droplet hollow cone ceramic nozzles
• compare deposits from one sprayer with another • fruit exposure – thin to singles
• halve the application volume and make a pass in both directions along the row
• Note that water sensitive papers do not provide a
reliable indication of spray droplet spreading on plant surfaces – especially where super-‐spreader spray adjuvants are used.
What to look for
The papers represent a repeatable, fixed-‐position
target. Given that leaves are free to move in the sprayer air stream it is quite likely that leaf deposits will be better than those seen on the papers.
However, the papers are not unlike fruit or branches which do not move as readily and the deposits on the papers can be regarded as a worst case look at
deposits from your sprayer.
There are four important things to look out for:
1) Major gaps in spray coverage – yellow papers where the spray is failing to penetrate or reach.
2) Uneven coverage – some papers heavily or totally
blued, while others are still mostly yellow. Even if there is an even spread of droplets on the poorly covered areas this area is underdosed relative to the
areas with greater coverage.
3) Droplet sizes and distribution – there is a useful guide available with the water sensitive papers that provides information on this area.
4) Runoff – (totally blue papers with streak marks),
especially if this occurs with concentrate spray applications.
Figure 9: A 5m tall spray pole with fixed target water senstive paper clips in a dormant apple tree Note use of folded vertical and horizontal papers at
approximately metre height intervals, with full blue wetting of visible papers from a high volume spray.
A template for recording water sensitive paper results is given on the following page.
LOCATION………………………………………………DATE………………..RUN # ……..
Block Mark Pole Position Sprayer
X marks trees X X
Water Rate (l/ha) X X Travel Speed (km/h)
Indicate wind direction with an arrow
X X Wind speed Direction Temperature of travel X X Orientation Facing/Upwind Distant/Downwind Top Surface Bottom Surface Height
…
…
…
…
…
