Post-harvest pre-planting applications of glyphosate
When glyphosate was introduced in 1974 it was initially used after the harvest in the autumn on stubble fields. This “post-harvest pre-planting” management is still an important tool for controlling weeds prior to planting the next crop. Farmers use this management strategy for winter crops especially, such as winter wheat and oilseed rape, which are often infested with annual weeds like black grass (Alopecurus myosuriodes) and rye grasses (Lolium spec.) that can be difficult to control before harvesting. Additionally, self-set plants from the previous crop may become established as weeds in winter crops and compete with the new plants, reducing their yields.
Since many annual weeds flower early and their seeds germinate immediately after harvest, farmers generally apply glyphosate in the autumn, 4 – 6 weeks after harvest, to clear fields of these weeds and volunteer crops. However, the timing of glyphosate application also depends on the climate conditions that year. If, for instance, the summer and autumn are cold, the seeds of many annual weed species will not germinate immediately after harvest, but ripen on the soil surface for approximately 30 days before they begin to sprout. In these cases farmers will apply the herbicide at a later time to catch weeds at full growth.
Post-harvest pre-planting management is also commonly used to control perennial weeds that live for more than two years, such as common couch (Elymus repens) and Johnson grass (Sorghum halepense). The control of perennial weeds is particularly relevant in Eastern European countries, where perennial weeds in agriculture are still common. Common couch for instance has been shown to reduce sugar beet and potato yields by more than 30%.
Post-harvest pre-emergence management
Another common application method for glyphosate herbicides is spraying after sowing, but before the new crop emerges. The “post-harvest pre-emergence” practice is used to control weeds that may have been transplanted or grown from seeds after the crop was planted. Having survived the cultivation process, these weeds will begin to grow rapidly, competing with the new crops. Farmers also fall back on this method when the weather has been too windy or wet for pre-planting spraying. Post-harvest pre-emergence is commonly used to manage sugar beet in the UK.
Last update: 21 November 2013