How to Set up and Operate your Boom Spray
Proper boom spray operation is essential for reliable and effective results. The following 8 factors must be considered.
Boom Height
Correct height is essential for uniform spray coverage and depends on nozzle spacing, nozzle angle and the height of the target. Most modern boom sprays have 110 ° flat-fan nozzles spaced 500 mm apart. These nozzles provide the correct double overlap when the boom is set 500mm above the target.
Set the height from the top of the target, not from the ground; to spray seedling weeds, the correct height is 500mm above the ground, but for weeds in an oat crop 150mm tall, the correct height is 650 mm.
Low boom height leads to uneven strips of spray. It is better for the boom to be slightly too high than too low.
Nozzle Offsetting
Nozzles must not be set parallel to the boom but at an angle of 15°. This prevents disruption of the spray pattern, which occurs if the sprays from adjacent nozzles hit together.
Some boom spray manufacturers provide a special tool to angle the nozzles. Otherwise, use a spanner, placing the nozzle tip in the jaws and turning the spanner until the shaft of the spanner is parallel with the boom. Some boom sprays have bayonet-type nozzles, which offset automatically.
Operating Pressure
A reliable pressure gauge located in the main pressure line to the boom is essential.
Operate at about 200–300 kPa (30–40 p.s.i. or 2–3 bars). Reducing operating pressure below this range is not a suitable way to reduce output. Buy a set of smaller aperture nozzles to apply low water volumes. Ensure that all nozzles are the same aperture and the correct size for the required droplet size and are suited to the operating pressure, speed and rate.
Operating Speed
Most boom spraying is done at 5–12km/h. Changing the speed changes the application rate. Select a speed to suit the most difficult part of the paddock and operate at that speed over the whole paddock.
Water and Chemical Rates
Water rates of 60–120L/ha are commonly used. Lower volume spraying (30–50L/ha) requires a higher degree of application accuracy. Read the recommendations on the product label.
If the boom spray is calibrated to apply, say, 80L/ha, then a 600L tank will cover 7.5 ha (600 ÷ 80). The amount of herbicide to apply at, say, 2L/ha is 15L/tank (2L/ha × 7.5ha).
Mixing Chemicals
When using tank mixes of chemicals, always check to ensure compatibility.
Mixing some chemicals can reduce their effectiveness or increase the risk of pasture damage. Compatibility charts can be found in the NSW Agriculture publication Weed Control in Lucerne and Pastures.
Never mix the concentrates.
Instead:
1. Fill the tank to one-third with water and start the tank agitation.
2. Add the first chemical.
3. Top up the tank to two-thirds with water.
4. Add the second and subsequent chemicals.
5. Add the final lot of water.
6. Always add wetting agent last.
Check the chemical labels for directions on tank mixing as some chemicals must be added in a particular order. For more information, see Agfact P7.3.1, How Much Water to Mix with Herbicides?
Spraying
When spraying, minimise spraying around corners as this leads to under- and oversprayed patches.
Some form of marking is essential for achieving full spray coverage and preventing costly overlaps and spray misses.
Take care and use proper protective clothing, especially when handling the chemical concentrates. Use a tractor with a fan-ventilated cab and appropriate air filters. Avoid spray drift to neighbouring paddocks.
Cleaning and Storage
Careful selection of filters and regular cleaning will reduce the likelihood of nozzle blockages.
Always flush the boom spray unit with clean water after use. Do not leave unused chemical mixes in the tank. To prevent contamination between different sprays, always flush the unit with water and then, using a mixture of 2% cloudy ammonia (1L in 50L water), wash down the inside walls of the tank and run about 20L through the lines and nozzles. Finally, flush thoroughly with clean water.
Caution:
Do not clean with cloudy ammonia after spraying with Ally® or Brush Off® (metsulfuron methyl) or Glean® (chlorsulfuron), as it can cause the release of poisonous chlorine gas. Use household chlorine bleach instead at 300mL in 100L of water.
When storing equipment at the end of the spraying season and after cleaning, run a mixture of water and miscible oil (the type used on lathes) through the pump and nozzles.
