Minimising summer spray drift risk

Nozzles, timing key factors in minimising summer spray drift risk


Nufarm spray expert Bill Gordon says farmers need to know best practice principles for summer spraying to avoid the risk of spray drift.

Nufarm spray expert Bill Gordon says farmers need to know best practice principles for summer spraying to avoid the risk of spray drift.

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There's been a lot of talk about chemical drift over the summer, but it is an issue that can be managed according to a spray expert.

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WITH a series of high profile instances of group I herbicide (phenoxy)  symptoms appearing on cotton and horticultural crops this summer, the result of  off-target  movement of spray droplets, a leading spray expert is calling for farmers to make good choices regarding summer spray programs.

Nufarm spray application specialist Bill Gordon was part of a series of workshops across the country over summer designed to educate farmers on best practice in terms of summer spraying.

“Summer spraying is a valuable practice for growers, but things can go pear shaped very quickly if things are not done at the right time, with the right sprayer setup,” Mr Gordon said.

He said in the case of inversions, chemical could be carried for more than 40 kilometres on the breezes that occur at night.

In the evening, the ground cools through back radiation promoting surface temperature inversions. As the air near the ground cools, the air flows over the surface becomes less turbulent meaning the air doesn’t mix as much, and droplets left in the air tend to stay in the air for a long time.

“This is why it is so important people know that the risks associated with spraying are very different during the day, compared to night when it comes to spray drift,” Mr Gordon said.

He said the hot temperatures in the middle of the day in summer often scared growers off spraying during the day.

However, he said with the correct assessment of the condition of weeds, particularly when soil moisture is still available, farmers could spray effectively during the day.

“If the weeds are not at the point of stress, then you can probably go longer during the day.”

In some cases, such as with tough summer weeds such as heliotrope, spraying during the heat of the day is actually more effective.

Overall, however, Mr Gordon said a lot of summer spraying was done in the cooler, often more humid night time air.

He said this could work well in terms of efficacy and plant uptake, but added it was critical spray applicators understood how conditions varied.

Bill Gordon demonstrates spray techniques to a group at Longerenong College, near Horsham in Victoria.

Bill Gordon demonstrates spray techniques to a group at Longerenong College, near Horsham in Victoria.

“We ran a trial near Narrabri where the same spray rig, with the same nozzle set-up worked at day and at night and it was found there was five times as much chemical in the air when the spray was applied at night due to the air movement.

“A lot comes down to how the air moves across the surface and the change in the type of wind speed required to create turbulence.”

“During the day, when the sun is heating the ground you can get turbulence at more than 4kph, but at night with cool ground that rate can increase as high as 12kph.”

“A t night you may need to be moving  at least 12kph just to help bring  air borne droplets back to the ground.”

He said farmers needed to be aware of when inversions were likely to occur and when they would be strongest.

“You often find autumn and spring, with large variations in maximum and minimum temperature, can have frequent inversion events.

Mr Gordon said one way of combating the risk of inversions was to alter the type of nozzle used, increasing the droplet size when using fully translocated products, such as Glyphosate or Group I herbicides.

He said products also varied in terms of the risk they pose to sensitive crops.

“We know a 2,4-D amine is a lower risk choice than a low volatility ester 2,4-D product for example.

“With other strategies, such as a double knock, you can probably feel more comfortable putting on a Group I with an extremely coarse droplet, when you know there is another pass with paraquat to come, it is all about keeping risk of drift down.”

He said getting the right adjuvant could also help farmers help to minimize drift, but the nozzles will always have the biggest effect on what gets into the air.  So the combination of nozzle and adjuvant is the best way to combat drift.

“Knowing your target weeds and what kind of droplets work best with them is also important.”

Mr Gordon said industry expected summer fallow spraying to continue to be a big deal.

With the growth of summer cropping, cotton and horticultural crops in particular, spreading into traditional winter-only cropping zone, he said farmers who had previously not had to factor in coexistence with other crops would now have to factor in the impact of potential drift events.

“Most of the heavy lifting in terms of minimizing drift will come from using the right nozzles.

“Finding an adjuvant to help you get the droplets a bit bigger is another useful way of minimizing drift concerns.”

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