How to avoid spray drift

Source: Saskatchewan Agriculture and Food

As pre-harvest spraying gets underway, a research scientist with Agriculture and Agri-Food Canada in Saskatoon is reminding farmers to take precautions to avoid spray drift.

Dr. Tom Wolf says spray drift can cause considerable economic and environmental damage.

“The environment is a foremost concern for both the public and for farmers. We ask that they make sure that, when they do spray, they protect anything that is a non-target, whether it is another crop, a body of water or a shelterbelt. Some of the herbicides we use in pre-harvest can be quite detrimental to water sources or shelterbelts. One of the most common products, glyphosate, can in fact kill shelterbelts outright if it is not applied properly, so spray drift control is very important during a pre-harvest application,” said Wolf.

Wolf says there are a number of tools and tips to prevent spray drift, but the most effective tool is located under a ball cap – the spray operator.

“Ultimately, it is the operator who has to make the choice about whether to spray or not and about how the spray will be applied,” explains Wolf, “but beyond that, weather is also a critical factor.”

Wolf says ideal conditions are a sunny day, with a slight breeze, and at least a couple hours after sunrise.

The fact that a slight breeze is ideal may seem counter-intuitive, but Wolf says there are benefits to a breeze.

“Most people look for calm days, but when it is calm, sooner or later there will be some wind and it will be difficult to predict what direction it will come from or when it will come. So, in order to prevent spray drift is it better to have a predictable wind direction,” said Wolf.

The other key factor in ideal conditions is to spray at least a couple of hours after sunrise. Wolf says that is to avoid temperature inversions.

“Temperature inversion occurs on most summer nights. It is a calm and stable atmosphere that will see any spray drift hang over the crop. That spray drift will stay concentrated in a stable atmosphere. That means it does not get diluted. So, when it does move off target, which it eventually will, it remains quite potent and can cause a great deal of harm. That’s why we want a slight breeze during spraying. The breeze disperses that spray so it actually mixes in the atmosphere so that the spray drift causes minimal harm,” explains Wolf.

However, Wolf concedes that ideal conditions can’t always be found.

“Let’s assume you are in a situation where you just simply have to spray. There are still a number of ways you can bring yourself back into a safe application scenario. One of those ways is to use the proper droplet size. Pre-harvest application is very well suited to the use of low drift nozzles such as an air induced nozzle. When you move to those nozzles, you can reduce your drift from a conventional spray by over 70 per cent. That is a very significant reduction,” said Wolf.

For more information on spray drift, visit the following websites:

* http://res2.agr.gc.ca/saskatoon/result/letter9703-lettre9703_e.htm
* http://www.agr.gov.sk.ca/docs/environment/cps0397.asp
* http://www.agr.gov.sk.ca/docs/production/faq_choosingnozzles.asp

For more information, contact:
Tom Wolf, Research Scientist
Agriculture and Agri-Food Canada
Telephone: 956-7635
E-mail: wolft@agr.gc.ca