Select your weapon
For spot spraying, (spraying individual weeds) a knapsack sprayer is adequate. However, if you need to spray woody weeds or vines, such as blackberries or lantana, a powered wand is required. A knapsack is incapable of putting out the volumes necessary to wet big blackberry bushes, for example.
Small boom sprays mounted on ATVs or tractor three-point-linkages (3PL) usually have the option of a hand gun running off the pump.
To spray weeds spread throughout a pasture, the usual equipment is:
- a small boom spray mounted on the back of an ATV
- tanks attached to the front and/or rear carry racks
- a small diaphragm pump running off the battery or a small 3PL boom on a utility tractor
- the pump powered by the tractor’s power take-off (PTO).
It is common for this equipment to include a hand wand for woody weeds and spot spraying. If it is an option, it is worth choosing for the added versatility it provides. Weed wipers are another alternative that can be used to stop weed seed set in crops or pastures.
There area a range of different types of weed wipers including rotary, blanket, wick and rope wipers.
Made to measure
Calibration involves measuring how much spray the sprayer puts out. Labels usually include two mixing rates: a dilution rate, for example, 100mL chemical per 1L water or an area rate, for example, 2L/ha of chemical in a minimum water volume of 50L/ha.
Dilution rates are only suitable for spot spraying. Rather than mix up and spray away, it is useful to know how much spray you are putting out, so you can avoid both over or under-application.
Over-application wastes pesticide and puts excess pesticide into the environment. Under-application generally results in a spray failure.
To calibrate a boom spray, you need to know how much each nozzle puts out, the swathe or spray width of the boom, and the speed of the sprayer. When you have these three figures, it is then a matter of putting them into the formula.
Nozzle output is measured using a measuring jug and stopwatch or tip tester. The swathe is the sum of the width of the boom plus one nozzle spacing.
Sprayer speed needs to be checked by timing the sprayer across 100m, rather than relying on the speedometer.
The correct nozzle needs to be selected to give the droplet spectrum required by the target, and to deliver the required output.
More and more labels specify droplet spectrum, for example, medium to coarse, and most labels will recommend an output or flow rate, for example, 50L/ha. Nozzles can be selected by looking up nozzle charts. These charts are available in hard copy, and also on the web.
You can learn more about calibration in pesticide training courses and calibration sheets are available. Training courses will also teach you how to read and use nozzle charts.