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Getting the best from your Mistblower

Tips for protecting tree crops

The way Mistblowers send clouds of spray onto tree crops can look like a rather hit-and-miss business.

However, taking some time to prepare the machine and understand droplet deposition can bring a good deal of science and accuracy to your spray days. And given the ever-increasing value of both water and chemical, it’s time well spent.

There should be no, or very few, droplets on the papers outside the canopy and an even distribution on the rest. You can measure a 1cm square and count the droplets, or just use the STP examples belowas a guide.

You want at least 20% coverage per piece, but no completely blue or “washed” papers.

“regular attention to detail will help you save money and get the best from your Mistblower.”

The first step is to fine-tune your Mistblower’s air distribution.

The method HARDI recommends is to tie ribbons to poles set in the ground beside some typical trees. Use four ribbons per pole – one each at the upper and lower levels of the canopy, and one each another 0.5m above and below. Then start the Mistblower and adjust the top and bottom deflectors so the air stream hits the two ribbons at the canopy edges, but barely disturbs the two ribbons further away.

You can now be sure you’re only treating the trees, without blowing extra chemical into the air.

Next, back this up with a deposition check using strips of Spray Test Paper (STP) clipped to the foliage or poles. (For large trees, put poles across the row width as well as along the tree line.)

Space the Spray Test Paper at 0.5m intervals along each pole, from 0.5m below the foliage to 0.5m above. Then spray the row of trees from both sides, starting at least 20m before the poles and continuing at least 20m after.

The speckle of blue dots on the paper will show you how and where your spray is landing. 

Larger droplets usually provide heavier deposition and better canopy penetration, but the higher application rates required can also lead to less uniform and ‘bottom heavy’ coverage. Finding the sweet spot means balancing the manufacturer’s recommended application rate with droplet size and spraying speed.



Accurate speed is also an essential part of accurate dosage. If your tractor has non-standard, worn or even slightly deflated tyres the speedometer won’t be reliable.

So at HARDI, we always advise growers to include a speed calibration run when they’re doing these other set-up jobs. The regular attention to detail will help you save money and get the best from your Mistblower.

Summarised from the HARDI Mistblowing Technique guide. You can download a free copy from myhardi.com.au