The presence of annual weeds in combinable crops at harvest can reduce combine efficiency, increase grain moisture and delay harvesting. To control perennial weeds the use of Roundup pre-harvest is particularly important as it usually results in more effective control than applications in the spring and does not delay subsequent field operations. Pre-harvest Roundup treatment gives more flexibility of cropping and more timely sowing in the autumn as well as easing the harvesting operation.
Perennial Weed Control
Using Roundup to control perennial weeds in the period immediately before harvest works particularly well because the weeds are actively growing and often at the most susceptible growth stage. The exception to this is in poor weather, such as drought, very wet or windy conditions, or if the weeds have started to die back. In these circumstances it may be better to treat the weeds in the stubbles.
Annual Weed Control
Annual grasses are quickly killed, along with cereal leaves and stems at the harvest management rates.
Annual broad-leaved weeds remaining green in a ripe crop reduce combining speed and efficiency as well as raising the average moisture levels. As the speed of kill with glyphosate is much slower for broad-leaved weeds than grasses, it can take longer than the statutory harvest interval for Harvest Management rates to kill these weeds.
Some weeds take a particularly long time to die back, namely:
- Annual Sow-thistle
- Fool's Parsley
- Pale Persicaria
- Black Bindweed
Where broad-leaved weed populations are very high or difficult weeds are present use the higher pre-harvest rates.