Pre-harvest applications for weed control and to enhance crop ripening
Generally, glyphosate applications before the harvest are used for long-term control of perennial weeds such as onion couch grass (Arrhenatherum elatius), bent grasses (Agrostis species) and common couch (Elymus repens), which commonly infest winter barley and oilseed rape, but also thistles (Cirsium arvense) that reduce the yields of sugar beet in Europe. These weeds die around harvesting time, meaning that the weed plants and their roots are not susceptible to post-harvest glyphosate treatment. If farmers are not able to remove them completely before harvest, their roots would remain in the ground and regrow after harvest, competing with the new crop. Moreover, glyphosate works more effectively on perennial weeds at the pre-harvest stage, since mature weeds move sugars down to their roots, transporting glyphosate readily to their roots and other plant organs.
In some European countries glyphosate is also frequently used to enhance crop ripening. This is particularly popular in countries like the UK, where summers can be wet and crops ripen slowly and unevenly - potentially leading to reduced yields and lower quality grain. Here, pre-harvest treatment helps farmers to harvest their crops more efficiently and at less cost. However, the deployment of pre-harvest management varies significantly between countries. In the Germany, for instance, only 4% of the total acreage is managed with glyphosate before harvest, while in the UK glyphosate is used on 78% of oilseed rape to facilitate harvest.
In some European countries such as the UK, glyphosate treatments are also used before harvest to control weeds and to accelerate maturation of oilseed rape and winter cereals (© Petra Bork/ pixelio.de).
As with all uses of glyphosate, pre harvest applications must be authorised and users must adhere to certain conditions in order to mitigate risks to human health, wildlife and the environment. In order to ensure the highest levels of safety for the food chain and consumers, pre harvest applications must only be performed when the grain has sufficiently developed. This is to prevent the product moving into the grain. Rather, application of glyphosate in these circumstances targets weeds and other parts of the crop such as the leaves and stems which could otherwise hinder harvesting.
Although pre harvest application does not result in glyphosate being absorbed into the grain, residual traces can sometimes remain on the surface of seed heads and pods. Residual traces have been found to be minimal and consistently well below levels which have the potential to pose risks to human health.
Last update: 19 March 2014