Couch grass control under organic conditions - a guide

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Problems with couch grass can be solved with knowledge of biology, prevention and the right control strategy. Common couch grass is a problem in organic fields on both sandy and clay soils and reproduces easily.

Mapping and spreading

Common couch grass grows almost all year round when the soil temperature is above 3 degrees. Therefore, it is possible to control common couch grass by starvation for most of the year.

An effective treatment is best carried out by mapping the presence of common couch grass in the field. Therefore, it is a good idea to record where in the field it is observed. Mapping the presence of couch grass can help to target mechanical control to avoid spread and propagation.

A good idea is to make a field map where root weeds are plotted. This makes it easier to target your efforts and prevent root weeds from spreading to the entire field.

Do not spread the couch grass runners to a clean part of the field. To avoid spreading couch grass into the field from boundaries or fences, avoid harrowing close to boundaries where couch grass is present. Harrow the outermost rounds last.

You can use FarmTracking to register root weed hotspots at field level, making it easy to keep track of root weeds. Then your crop consultant can also keep an eye on MarkOnline in the office, and you can plan the right control strategy.

Strategies for control

Interrupt growth immediately after harvest

Stop the growth of the couch grass immediately after harvest with a full cut. This is essential for effective control and the sooner you get started, the better.

Cutting back the growth of couch grass with full cut after harvesting effectively stops the development of runners.

Types of harrows for full cutting:

• Use a wing-cut harrow or shallow peeling plough at a depth of 8-15 cm and deepest on sandy soils, undercutting the runners and exposing them on top of the plough furrow

• When using a stubble harrow, make sure you achieve full penetration

• The cut is immediately followed by harrowing, which pulls the runners up on top of the soil.

• If you use KvikUp or Kvikkiller, this can be done in one pass.

A good tip is to go into the field with a spade and check how deep the runners are in each field. If the roots are deeper than the harrowed layer, it may mean that fresh runners will appear in the upper layers if the subsequent ploughing is deeper than the harrowing.

Weaken the runners

There are two ways to weaken the runners

Starve the runners by interrupting growth as soon as the plant has 3-4 leaves. Dry out the runners by exposing the roots on the soil surface.

Trials have shown an effect of 51% reduction by combined starvation and drying with repeated harrowing (Landsforsøgene 2009).

Starvation

Starvation is most useful in autumn with humid weather conditions, as control by the starvation method is achieved by allowing the runners to set green shoots. By repeatedly harrowing when the plant has 3-4 leaves, the plant's roots are depleted of energy, eventually making it impossible for the plant to germinate. Further division of the roots can promote starvation.

It is important to harrow sufficiently, otherwise nutrients will build up in the roots. It is better to harrow too early than too late.

Starvation can be done in the autumn after harvest if there are prospects of damp weather, or in the spring followed by a good ploughing, which gives the weakened runners less opportunity to reach the soil surface again.

Drying

Drying can be used if a dry period of at least 14 days is expected in the autumn or spring, or in the winter months if a longer period of frost is expected. Drying out destroys the buds of the runners so that they cannot germinate.

The method is carried out by pulling the runners up to the soil surface by repeated harrowing withot damaging the roots. To bring the roots up to the soil surface, a harrow with full cutting action can be used to slice through the roots, along with  rotary tines, a post-harrow or other equipment can be used to exposes them on the soil surface.

• In clover grass fields, grazing and mowing can help to keep the couch grass down but not control it.

• In crops to maturity, there is no control option.

Mini summer fallow

In a mini summer fallow, the soil is kept bare during the summer months. This provides effective control of all root weeds as it takes place at a time when these weeds are growing vigorously, and because the strategy involves both starvation and drying out the roots and runners.

This method is used if there is a major problem with couch grass or if there is a mixed population of root weeds, such as thistle, creeping bentgrass, pigweed, etc. that cannot be effectively controlled by other means.

Mini summer fallowing can be carried out by repeatedly harrowing during the period of 1 June and 1 August using a heavy-duty stubble cultivator with wing blades that provide full cutting-through of the soil. The advantage of a mini summer fallow is that the control is carried out during a period when there is often low humidity.

Strategy to keep the soil black with mini summer fallow:

• Sow spring seed in the spring.

• Carry out ploughing or trimming in June.

• Keep the soil black with repeated harrowing with full cutting in June and July.

• Do a good ploughing at the end of July and sow yellow mustard or oil radish as a catch crop.

• Plough again in the spring and sow a competitive spring crop.