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When Spray Drift Hurts JUN 4 2013 | Producers | Blog Post

Pesticides have their uses when applied properly to a crop: with the right care and attention, herbicides, insecticides, and fungicides can be applied safely and effectively to give our crops the greatest opportunity for success. But when pesticide application occurs because of spray drift, chances are your crop – and your livelihood – will suffer.

Each and every grower and applicator is responsible to seek the required accreditation (for example, a pesticide applicator’s license), and in a best-case scenario, that accreditation will ensure that any applicators in your area will employ the utmost care and attention and will understand the rate, possible carry-over, and any conditions associated with the agricultural pesticide he or she is applying. But as with any other risk associated with farming, you can’t always rely on the best-case scenario to work out.

As producers, it’s dangerous to assume that pesticide applicators have taken the time to know what’s being grown on each of your fields, have excess time on their hands during spray season, don’t have to spray early or very late in the day, and know fully what effects the wide assortment of chemicals available to today’s applicators can have on each of your crops. We all lead busy lives and need to make good progress each day of our available window for spray timing, and checking on details can seem burdensome. This is true of our own operations, as it is for our neighbours and others who make their living applying agricultural chemicals.


  • Droplets are 5 microns wide
  • Droplets take 66 minutes to fall 10 feet
  • Droplets laterally travel 3 miles when falling 10 feet in 3 mph wind

Very Fine Spray

  • Droplets are 20 microns wide
  • Droplets take 4.2 minutes to fall 10 feet
  • Droplets laterally travel 1,100 feet when falling 10 feet in 3 mph wind

Fine Spray

  • Droplets are 100 microns wide
  • Droplets take 10 seconds to fall 10 feet
  • Droplets laterally travel 44 feet when falling 10 feet in 3 mph wind

Medium Spray

  • Droplets are 240 microns wide
  • Droplets take 6 seconds to fall 10 feet
  • Droplets laterally travel 28 feet when falling 10 feet in 3 mph wind

Coarse Spray

  • Droplets are 400 microns wide
  • Droplets take 2 seconds to fall 10 feet
  • Droplets laterally travel 8.5 feet when falling 10 feet in 3 mph wind

Fine Rain

  • Droplets are 1,000 microns wide
  • Droplets take 1 second to fall 10 feet
  • Droplets laterally travel 4.7 feet when falling 10 feet in 3 mph wind

And losses can be extreme. Take, for example, a simple 2,4-D mixed with Banvel application happening along a grass-line next to a quarter-section of lentils, applied with small droplet size and with a fixed boom sprayer that is elevated above the ditch intended to be sprayed. Now, let’s assume a slight breeze is blowing and the chemical wafts gently over the crop. In this example, we’ll say it reaches out about a third of the way across the field, so that means it covers an area of one-half of a mile by one-third of a mile (in other words, 2,640 feet long x 1,760 feet wide). That means about 107 acres of crop have had a highly injurious chemical applied to them.

This can result in a variety of problems, including stunted crop growth, more weed competition, higher production costs, greater marketing challenges, higher storage costs if needing to store production from different parts of the field separately or for a longer period of time, lower yield, and lower grade due to plants maturing at an uneven rate through the remainder of the growing season.

In this hypothetical example, let’s say bin space was at a premium, and the entire crop was mixed at time of storage. The grade dropped out of the No. 2 range, and to make matters worse, the expected yield wasn’t accomplished. There was an 8 bushel per acre yield penalty on the affected acres, presumably worse right along the ditches and getting less severe the farther one travels out into the field. These sorts of gradual changes in crop stand and viability can also be difficult to diagnose unless a problem is suspected because there’s no clear line where, on one side, the crop is full and lush and, on the other, it’s sparse and sickly.

Lentils have been priced well the last few years, and a No. 2 lentil crop could be sold for $0.30/lb as recently as the 2010 crop. A No. 3 was about $0.20/lb. The overall yield across the 160 acre field could easily have been 32 bushels per acre, but with the 8 bushels lost over 107 acres, the resultant yield didn’t look nearly as good, coming in at 27 bu/ac. So if the crop had been unaffected by spray drift but everything else had remained equal, the gross return would have been $576.00 per acre. With the problems experienced, the actual return was much less, about $324.00 per acre. In total, gross income fell from $92,160.00 (without spray drift) down to $51,840 (with spray drift). Lost revenue for this field is $40,320.00.

Not only does this represent an economically significant loss, but it could also be multiplied by a larger number of fields. If the producer in this case study would have planted three fields, or even five fields, instead of just one field of lentils, and each adjacent area had been sprayed the same day and in less than ideal conditions with less than perfect equipment, we would have arrived at an even higher loss.

Determining the cause of crop degradation can also be difficult, in some cases. Maybe the year has been wetter than usual and some of the crop was looking yellowish, or even necrotic, in places prior to the chemical application and spray drift. Even in perfect conditions, it may not be noticeable for a week or more after the actual date of application, and by then, the applicator is long gone. Before long, the crop may be drying down, and damage may not be nearly as visible. It gets harder, at that point, to prove what caused a poorer crop in parts of the field. Growers must stay vigilant in watching their crops throughout the growing season to ensure a fast response time if any yield or quality limiting factor occurs – including spray drift.

It’s incumbent upon anybody applying pesticides to do so carefully and with the health of all crops in the area in mind – but producers must also do all that is required to be profitable. Knowing what chemicals are being applied on your own land and knowing the practices of applicators on all sides of each field is a good place to start during spray season.

For a full list of registered chemicals and details pertaining to each chemical’s label, consult the Alberta Crop Protection Guide (also referred to as The Blue Book). Visit Alberta Environment and Sustainable Resource Development for more information about the pesticide applicator certification program in Alberta.