Watch speed to get best nozzle performance

Crop spraying is moving into the fast lane with today's new sprayers. But can nozzles keep up? It's time for a renewed focus on spray pressure to strike the right balance, says Dr. Tom Wolf.

Posted: June 7, 2011

"What nozzle is the best for me?"

This is the question Dr. Tom Wolf of Agriculture and Agri-Food Canada gets from farmers more than any other. Problem is, it's only part of the real question they should be asking.

"It would be nice if you could just pick the right nozzle and get the right results," says Wolf, a leading researcher and thinker in the area of crop spraying "But it's not that simple."

Equally important considerations are the details of how you plan to use the nozzle and how that lines up with the priorities of your operation, he says. Today this needs more attention than ever as advances in new sprayers that enable greater scale and speed are out-pacing the ability of nozzle technology to keep up.

Of most concern for Wolf is that spray operators recognize how higher travel speeds impact spray pressure, which in turn impacts nozzle performance and the overall result.

"Some spray operators assume once they make the 'right' nozzle decision, they can use the nozzle with a broad range of approaches and expect the results they want," says Wolf. "The fact is, travel speed is linked to spray pressure, and the pressure with which you operate a nozzle has a tremendous impact on the result. You may be too coarse or too fine, depending on your travel speed."

Check manufacturer information

Spray operators need to look at the whole picture to determine the right approach, he says. A good starting point is to recognize that each nozzle type has a unique spray pressure range and unique spray qualities within that range.

Pressure affects the spray pattern (fan angle) and the spray quality (droplet size range), he says. Both of these affect coverage, overlap, and spray drift, so it's important to get them right.

"Farmers need to get information that is specific to the nozzles on the spray boom," says Wolf. "This can be found in catalogues from nozzle manufacturers."

Recognize limitations

A key difference in spraying today compared to years past is there is greater potential for variability in results, says Wolf.

"If you go back 20 years or more and we just had pull-type sprayers and we went fairly slowly, the nozzles were able to meet the demands of that kind of an operation quite easily. You set the pressure and you went that speed and that was that. You had consistency - not just in droplet size, but you also in boom height. What we have now with these faster sprayers is a situation where consistency is much more difficult to get."

Today, nozzles are challenged to operate not just at higher speeds but over a wider pressure range, he says. Some nozzles are better suited than others to handle these challenges. Some higher-end options such as variable-rate nozzles are one example. But as a whole it's been difficult for nozzle technology to keep up. "All nozzles become coarser at lower pressures and finer at higher pressures," says Wolf. "We haven't found an effective way around that."

Auto-rate not a silver bullet

Even automatic rate controllers, which are now standard equipment on almost all new sprayers, are limited in their ability to help nozzles perform better at higher speeds, he says.

A rate controller allows the applicator to enter a desired application volume and the controller sets the spray pressure that gives the necessary flow for the application volume and sprayer travel speed being used.

"In practice, this means that higher travel speeds result in higher spray pressure, and vice versa," says Wolf. "But rate controllers aren't smart enough to know how pressure affects nozzle performance. Some nozzles don't work well at low pressures. Others do a poor job at high pressures. Some sprayer pumps may even have a problem generating some of the higher pressures a rate controller calls for."

Develop a balanced strategy

So what's the best approach for producers to take? For starters, spray operators need to know the right spray quality for the job at hand, says Wolf. They should then find a combination of nozzle type and operating approach that can deliver that result.

"Use manufacturers' charts to identify the spray quality your nozzle will likely produce at your expected application volume and travel speed," he says. "If it's a poor match, a different nozzle may need to be found."

Slow speeds out of a nozzle's operating range can also pose a problem, he says. "Operators also need to identify and be conscious of the lowest spray pressure at which their nozzle will still produce the desired result, and figure out at what travel speed they reach that pressure. "If the rate controller calls for 30 psi at a speed of 10 mph, then slowing down any further will very likely result in poor pesticide performance"

Once producers have the right information, perhaps the best advice is to not be afraid of compromise. "For some spray operators using new sprayers, it may be that they need to slow down and spend a bit more time in the field," says Wolf. "That's a compromise worth taking if it means a better overall result."