Crop Desiccation

Is it safe to eat a crop that has been desiccated?

As of October 17, nearly 81% of Saskatchewan’s crops were harvested (91% in Manitoba & 73% in Alberta). When compared to the 5 and 10-year rate of harvesting averages it looks like our farmers are on track. However, after a relatively promising summer, storm clouds brought larger than normal precipitation and snow. What you might not be aware of is that when crops and fields are wet, harvesting conditions are less than ideal. It’s likely that many Prairie farmers had to rely on desiccation to get their crops off this fall.

What is Desiccation?

The term desiccation means to ‘dry up’. In crop production this means to dry the plant, making it easier to harvest. The optimal time for harvest is very short. This means that farmers need to get their crops off as quickly as possible to ensure they get the highest quality and therefore higher prices. When combining a crop, the cut section of the plant is thrashed in the machinery, removing the seed from the straw. If the straw is too wet, it becomes difficult to properly separate the two, meaning that less crop is harvested as it passes through the combine.

There are two types of desiccants: true desiccants and pre-harvest herbicides. Both are applied to a mature plant prior to harvesting to achieve relatively similar results. In addition to physically drying the plant, if the crop is desiccated properly, there is a reduced risk of weather damage or shattering loss. A true desiccant is a contact herbicide; rapidly killing and drying out the above-ground portion of the plant over a few days. A pre-harvest herbicide is a slower acting desiccant which is absorbed and translocated to the root. This process of killing the plant at the root can take up to three weeks.

Should we be worried about chemical residues?

In Canada, there is no need to worry. This is because Health Canada regulates the pesticides maximum residue limit (MRL) that are permitted on our foods. The MRL is set well below the amount which could raise health concerns. A 0% tolerance for chemical residues simply does not exist in our food supply chains, regardless of the production process. Virtually every food we eat has some level of chemical residue on it, even organic foods.

Desiccant residues and toxicity levels

Canadian MRL (ppm) LD50 (ppm) LD50 (ppm) LD50 (ppm)
Lentils Wheat Rat Mice Rabbit
Reglone (Diquat) 0.2 0.2120233188
RoundUp (Glyphosate) 4 556001538Up to 10000
ReferencesHealth Canada. (2016). Maximum Residue Limits for Pesticides - Diquat. Health Canada. (2016). Maximum Residue Limits for Pesticides - Diquat. http://pr-rp.hc-sc.gc.ca/mrl-lrm/index-eng Health Canada. (2016). Maximum Residue Limits for Pesticides - Diquat. http://pr-rp.hc-sc.gc.ca/mrl-lrm/index-eng Health Canada. (2016). Maximum Residue Limits for Pesticides - Diquat. http://pr-rp.hc-sc.gc.ca/mrl-lrm/index-eng Health Canada. (2016). Maximum Residue Limits for Pesticides - Diquat. http://pr-rp.hc-sc.gc.ca/mrl-lrm/index-eng Health Canada. (2016). Maximum Residue Limits for Pesticides - Diquat. http://pr-rp.hc-sc.gc.ca/mrl-lrm/index-eng
Pesticide Management Education Program. (2016). Diquat dibromide. Pesticide Management Education Program. (2016). Diquat dibromide. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/diquat-ext.html Pesticide Management Education Program. (2016). Diquat dibromide. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/diquat-ext.html Pesticide Management Education Program. (2016). Diquat dibromide. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/diquat-ext.html Pesticide Management Education Program. (2016). Diquat dibromide. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/diquat-ext.html Pesticide Management Education Program. (2016). Diquat dibromide. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/diquat-ext.html
Pesticide Management Education Program. (2016). Glyphosate. Pesticide Management Education Program. (2016). Glyphosate. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/glyphosate-ext.html Pesticide Management Education Program. (2016). Glyphosate. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/glyphosate-ext.html Pesticide Management Education Program. (2016). Glyphosate. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/glyphosate-ext.html Pesticide Management Education Program. (2016). Glyphosate. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/glyphosate-ext.html Pesticide Management Education Program. (2016). Glyphosate. http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/glyphosate-ext.html

Reglone and Roundup are the most widely used true desiccant pre-harvest herbicide. Shown in the residue and toxicity table above, we can see that Canada only allows a very low dosage of Reglone’s active ingredient. The means in every kilogram of dry lentils consumed treated with Reglone, you will ingest only 0.2 mg of diquat. This active ingredient is only acutely toxic and is rapidly eliminated through our digestive tract.

Lethal Crops?

The residues on our crops are not lethal at normal rates. If you look at the lethal dose to 50% of the experimentally fed animals (LD50), we find that our desiccants residues should not be a health concern. Assuming humans are as sensitive chemical residues as rats, roughly 600 kg (1322 lbs.) of lentils would be needed to be consumed over a short period to raise lethal concerns of diquat. When you look at glyphosate, it’s even less likely to be toxic, as the chemical is poorly absorbed by our digestive tract.Lethal Crops?

Farmers little helper

Farming is a risky business. They never know what the weather has in store. Luckily our farmers have desiccants to help them quickly get the crop off without losing yield, quality or compromising our food safety.