Take the opportunity to control weeds before winter cropping
With the cereal harvest complete, Teagasc Crops and Potato Specialist, Shay Phelan reminds us that the next couple of weeks offer an opportunity to control problem weeds in fields destined for winter cereals.
With the cereal harvest complete, tillage farmers have a few weeks before autumn drilling starts again. For those growing winter oilseed rape, however, drilling is currently underway.
This couple of weeks can be used to control problem weeds in the fields that are intended for winter cereals.
Grass weeds like bromes, wild oats, blackgrass, Italian ryegrass etc., as well as broadleaf weeds and volunteers, will have a great chance to grow over the extended period this year before drilling starts.
It is important, therefore, that growers walk all fields and identify problems that can be treated between the two crops with a non-selective herbicide like glyphosate. Such action should reduce the pressure on winter cereal herbicides and make choices in crops much easier.
Many weeds or volunteers, like docks, scutch, sow thistle, volunteer potatoes etc., store carbohydrate below the soil surface in rhizomes, tap roots or tubers.
At this time of year, the plant puts a lot of its reserves into those underground storage systems in preparation for the following year.
While cultivation can give some control, quite often – especially with rhizomes – all it will do is chop the rhizome into small pieces and spread the problem. The most effective method of killing those rhizomes or underground stores is by using a herbicide.
As the plant moves reserves into the underground stores, glyphosate, for example, will be moved through the plant in the same direction and effectively stored in the storage vessel. This will eventually kill that underground store and prevent the rhizome, root or tuber from growing or producing new growth in the spring.
Figure 1: Potato volunteer with daughter tuber
In the case of potatoes, these volunteers will act as reservoir for potato blight in the new season if they survive the winter. We also see that where they grow in the spring, it can be very difficult to control them in crop. In such instances, it would take multiple applications of herbicides, which may not be possible either legally or physically, to control the different flushes of plants as they emerge from different depths.
If the field is intended for a spring crop, remember that after the application of a non-selective herbicide you must stubble cultivate to encourage some green cover on the field over the winter months.
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