Crop desiccation

Crop desiccation can improve the efficiency and economics of mechanical harvesting. In grain crops such as wheat, barley and oats, uniformly dried crops do not have to be windrowed (swathed and dried) prior to harvest, but can easily be straight-cut and harvested. This saves the farmer time and money, which is important in northern regions where the growing season is short.[5][6] In a non-food crop such as cotton, reliance on natural frost may be too late to be effective in some regions. Thus leaves that remain on the cotton plant will interfere with mechanical harvesters and stain the white cotton resulting in a lower quality grade; herbicides which cause both defoliation and desiccation reduce these problems.[7]

Desiccation can improve the uniformity of a crop. It may correct for uneven crop growth which is a problem in northern climates, during wet summers, or when weed control is poor. Plants that have naturally reached the end of their maturation may be mingled with plants in earlier stages of growth; controlled desiccation evens that out. This also increases uniformity of moisture content in grain, which has positive economic benefits in the storage of the grain and the price of the grain.[5][8]

Desiccation can enhance the ripening of a crop. With sugarcane, for example, glyphosate application increases sucrose concentration before harvest.[9] With grains, for example, as a consequence of crop plant uniformity as noted above, grain ripeness can be made more uniform through the same process.

Several additional advantages of desiccation have been cited: harvest can be conducted earlier; weed control is initiated for a future crop; earlier ripening allows for earlier replanting; desiccation reduces green material in the harvest putting less strain on harvesting machinery.

Examples of crops that may be subjected to pre-harvest desiccation include:[5][7][9][10][11][12][13]

• Cereals/Grains such as barley, oats, rice, sorghum (millet), and wheat
• Flax
• Cotton
• Legumes including beans (common, fava, garbanzos, etc.), lentils, peas, and soybeans
• Maize (corn)
• Mustard
• Oilseed such as canola, linseed, rapeseed, safflower, sunflower, and soy
• Potato
• Sugarcane
• Sunflower

In agricultural parlance, desiccation is divided into two distinct groups: "true desiccants" and pre-harvest systemic herbicides.[14][15] True desiccants are not chemical desiccants, rather they are contact herbicides which kill only the parts of the plant they touch. They induce plant death/defoliation rapidly and dry down occurs within a few days. True desiccants do not often provide good weed control because killing only the top growth may allow plants to begin re-growing again. In contrast, systemic herbicides are absorbed by foliage or roots and translocated to other parts of the plant. They poison metabolism throughout the plant thus the process is slower, with die off and dry down taking up to a couple weeks.

Herbicide residue in food has been raised as a concern. Residue quantities are regulated by Codex Alimentarius of the Food and Agriculture Organization of the United Nations.[25]

In July 2013 Austria banned the use of pre-harvest glyphosate citing the precautionary principle.[26] In April 2015 an oat buyer in Western Canada announced that it was refusing oats in which pre-harvest glyphosate had been used.[27][28]

Glyphosate was found in 5–15% of cereal crop samples tested in the UK between 2000 and 2004, although never exceeding the Maximum Residue Level of 20 mg/kg.[22] A survey of British wheat in 2006-2008 found average levels of 0.05–0.22 mg/kg with maximum levels of 1.2 mg/kg.[29]

Evidence that traces of glyphosate used on crops could make its way into a final, processed food product was raised in 2016 by a German environmental group, Munich Environmental Institute (note that this example does not distinguish between specific crop desiccation use and general use). The group issued a report that stated glyphosate was detected in Germany's 14 most popular beers, ranging from 0.46 to 29.74 micrograms per liter, noting that the German government limit for glyphosate in drinking water is 0.1 microgram per liter.[30] However, the German government's Federal Institute for Risk Assessment made an official comment that those levels did not pose a risk to consumer's health, emphasizing that “An adult would have to drink around 1,000 liters (264 U.S. gallons) of beer a day to ingest enough quantities to be harmful for health.” An industry group, Brauer-Bund Beer Association, asserted that the results weren't credible because of insufficient sampling and that its own monitoring system for malt never detected glyphosate levels above maximum permitted levels. Separately, in 2020 scientists from the Max Rubner-Institut published a study about correlations between trace levels of glyphosate in human urine with consumption of various food types.[31] They found no relationship between traces of glyphosate and the consumption of beer. Neither did they find an association with bread, honey, mushroom, and soy products but there was a correlation with pulses (legumes).

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