Part article taken from Crop Production Magazine
Written by Robert Harris
Most spray booms are carried too high, compromising efficacy and leading to excessive drift, reckons Chris Martin of Agrovista. The reason, he says, is that booms are getting wider, with too little thought being given to stability, while forward speeds are also increasing to maximise work rates, making the boom less stable. “The key to optimum performance is to get the nozzle close to the target, while still achieving the correct spray pattern. The biggest problem these days is that the opposite is happening. Not only are many booms unable to spray below 60-70cm, they’re actually being carried higher.” As boom height increases, the spray pattern suffers and drift increases rapidly –– as much as eight times higher at a boom height of 100cm compared with 50cm, he explains. “If you can reduce your boom height below 50cm, that’s a real step in the right direction.” To achieve optimum coverage you want higher water volumes while retaining a finer spray quality, especially important on difficult targets such as small blackgrass, he continues. “Using 25cm spacing, rather than 50cm, means you can double the water volume being applied across the boom without losing spray quality. Because the boom is so close to the target you can use an 02 or 025 nozzle without drift becoming a major problem. “You have 64 times as many droplets using a fine nozzle with a droplet diameter of 100 microns than a coarse one with droplet diameter of 400 microns at the same water volume. This achieves much more even coverage as the spray almost paints the target rather than relying on big droplets spreading out.” This can make a huge difference, for example Agrovista trials over many years have consistently shown that up to 50% better blackgrass control can be achieved from the same pre-emergence products through using better application. Forward speed can also be increased when nozzles are close to the target without sacrificing performance, Chris Martin adds.
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