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Pre-harvest intervals

Understanding and following the rules for pre-harvest pesticide application can save you a lot of time and money

In a year of unusual conditions across much of the Prairies, some unusual problems arose. Pre-harvest interval, the time between the last application of pesticide and the safe harvesting of edible crops for immediate consumption, was a much bigger consideration than usual because of the need for late-season spray applications.

With a strict tolerance approach to residuals in crops headed for human consumption markets, playing fast and loose with recommended intervals could be a costly gamble.

In many cases it’s simply a matter of not fully understanding the requirements.

The requirements

The Canola Council of Canada printed this definition of the pre-harvest interval in it’s August, 2012 issue of Canola Watch: “The pre-harvest interval is the number of days that must pass between the last application of a pesticide and cutting of the crop. Cutting is either swathing or straight cutting. From the end of flowering to physiological maturity usually takes about 25 days in Manitoba, 30 days in Alberta, with Saskatchewan in between.”

“Some confusion exists about the exact meaning of harvest in these situations,” says Shannon Friesen from the Saskatchewan Ministry of Agriculture. “When you’re talking about pre-harvest interval you have to back up from the date a crop is swathed or straight-cut, not just combined.”

The interval is based on the number of days it takes for the chemical, or residual, to break down in the plant. No traces of chemical can be found in seed destined for human consumption markets, so intervals can vary greatly, depending on the crop kind and the treatment applied.

All commercial products have clearly defined intervals on the label. Read them carefully and be sure you understand the impact of the product you’re choosing.

Remember that the break-down of residuals occurs only in the plant, not in the seed, so storage time after harvest has nothing to do with the required interval period.

Residuals on wheat crops tend to be less of an issue as wheat midge spraying (for example) happens earlier in the life cycle of the plant and any product is usually broken down well before the crop is cut. Pre-harvest interval doesn’t refer solely to pesticides. If you desiccate crops of any kind the treatments used will also carry well-defined pre-harvest interval requirements.

Greg Sekulic, Agonomy Specialist for the Alberta/B.C. Peace with the Canola Council of Canada, believes that farmers are doing a very good job of abiding by the regulations.

“By and large, most producers are well informed and doing a terrific job of adhering to the guidelines,” he says. “Difficult circumstances this past fall created situations that advanced harvest by as much as three weeks in some areas. That can be tough to deal with when you’re talking about pre-harvest intervals, but I think it was very well managed.”

The consequences

In 2012, severe infestations of bertha armyworm warranted late-season treatments that strayed perilously close to interval guidelines. In an effort to save endangered crops farmers may have underestimated the important days to harvest guidelines.

“There were a few issues in 2012, mainly because of late spraying for bertha armyworm, which was really bad this year,” says Friesen. “Random testing for residuals goes on all the time and results are incredibly accurate. It’s really not worth taking the chance that residuals can be traced back to your farm.”

Most farmers are aware of the consequences of playing with the interval period. With traceability protocols that can precisely pinpoint which product entered which bin on which day, there’s no place to hide. The consequences can be severe and costly.

“Having a boat rejected in Japan can result in fines of up to four hundred thousand dollars,” says Sekulic. “And the problem goes straight back to the individual producer, because the traceability is accurate enough to ensure that.”

Sekulic maintains that sound information is always the best defense. In an age of instant information made possible by social media, growers learn about potential hazards quickly, and are equally quick to react.

“The social media chatter was lively this fall and caused some concern, “says Sekulic. “The problem with Twitter is that it’s impossible to explain intricacies in 140 characters. But it’s relatively easy for growers to find the reassurance and information they need if they take it a step further. Our website gives a very clear picture of all you need to know about our export-ready program.” (Find the Canola Council’s website at †

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