Expert Advice on Getting Rid of Couch Grass
Article by David Marks
Couch grass (Latin name Elymus repens) is a quick growing, invasive type of grass which appears to contribute nothing to the overall appearance or productivity of a garden or allotment. Another commonly used name for this weed is Twitch Grass. It is a pain in the neck in your garden and mine, nothing more, nothing less.
This article explains several methods, organic and chemical, for removing and eradicating couch grass. Use the navigation box below to skip to the section most important to you if you don’t have time to read the entire article.
HOW DOES COUCH GRASS GROW
Although couch grass is considered a weed by UK gardeners and allotment holders it does actually have a use in some circumstances! Firstly, in some parts of the world couch grass is encouraged because it is a primary source of food for cattle and other animals. Its second most common use is to bind soil together to prevent erosion by wind and water.
Couch grass arrives in your garden or allotment initially by two means. By far the most common is through small root parts in the soil of plants which are transferred to your garden.
The second is by means of seeds. Insignificant flowers are produced in July / August time and these form seeds which can be spread by wind, water and carried on wildlife such as birds. Once it arrives in your garden however, forget about it spreading via seeds, it is the roots which enable it to colonise large areas quickly.
Couch grass seeds
When a root establishes, it send up grass stems, typically every 5 to 10cm along the root. The grass stems absorb energy from the sun which allow the roots to grow further. The roots store unusually large amounts of energy and they can continue to grow and survive for long periods of time without energy from the sun. Eventually they will die if they do not receive sunshine.
PROBLEMS CAUSED BY COUCH GRASS
Couch grass roots also secrete acids and other phytotoxins (poisons for other plants) which reduce the ability of surrounding plants to absorb nutrients from the soil. This has a direct impact for gardeners not only when the grass is growing but also when it is killed (rather than removed) by herbicides or excluding light. The reason for this is that, as the roots of Couch Grass decompose, they still secrete phytotoxins which can damage new plants.
Very little conclusive research has been conducted on how long these phytotoxins remain in the soil after couch grass has been killed. Our investigations suggest that the ground is partially “poisonous” to new plants for a month or so after couch grass is killed. The best research we could find was this document here.
The solutions we propose below to eradicating couch grass are based on three situations:
- Where this weed has established itself amongst other cultivated plants, this is the typical situation in a UK garden.
- Where the weed has established itself on a patch of land that is uncultivated. This is a typical situation for a new allotment or patch of land that has not been cultivated for some time.
- Where couch grass has taken hold of an existing lawn area.
Whichever of the methods you use below make sure that you dig a trench around the treated area about about 45cm wide and 15cm deep. This will allow you to see any roots crossing from the untreated area to the treated area and easily remove them.
KILLING COUCH GRASS WITH HERBICIDES
Herbicides are garden chemicals designed to kill plants, such as Couch Grass, which produce green growth above ground. The most effective herbicides (by a very large measure) available to amateur gardeners in the UK for killing grass have the key chemical ingredient glyphosate. This chemical is extremely efficient for killing grasses but it also has some potential disadvantages which are:
A significant proportion of people believe or suspect that glyphosate damages the environment, wildlife and humans. This a factual article so we won’t discuss this subject here, just be aware that concerns do exist. To investigate further simply type in something like “glyphosate poison” into your favourite search engine and research away.
For those who want a starting point for research on this subject try this article here. It has lots of links in the text to help you widen the research area.
If you do this research, weigh it up with the implications of not using a chemical such as glyphosate. There are implications and you need to be aware of them as well as the possible problems.
If this method of killing glyphosate is to be used on large areas we suggest that it is most effective when the following method is used:
- If the area contains weeds taller than 5cm / 2in, use a strimmer to clear the area of most of the top growth. Rake away the strimmed top growth to fully expose the weeds to sunlight. This task is best done in April time for effective control of Couch Grass. It will stimulate the grass into maximum growth mode.
- Wait for two weeks to let the grass form new growth. Then spray with the herbicide following the instructions on the packet or bottle. This includes only spraying when the ground is relatively dry and no rain is forecast for 24 hours or more.
- Leave the area alone for three weeks for the effects to be seen. If some weeds are still present undamaged, re-spray those surviving
KILLING COUCH GRASS BY SMOTHERING IT
It is often used in conjunction with the “dig it out” method in the next section. One patch of weeds is smothered and another area, required in a shorter time, is dug.
Smothering couch grass and other weeds works on the basis that if all light is prevented from reaching them, they will die. For best results, cover the weeds for nine months to a year. Lots of material can be used to cover the weeds, the most common are listed below:
Weed suppressing fabric bought online (the cheapest source) or at your local garden centre / diy store. It is typically sold in two weights, 50g and 100g. The heavier the material, the more durable it is. However for most uses, 50g weight is more than adequate.
If the weeds are much taller than 5cm / 2in high, strim them first to allow the fabric to sit evenly on the surface. Rake away the strimmed weeds and then lay the fabric on the top. The fabric will need to held in place to stop it blowing away. Stones or loose earth are ideal for this purpose.
When the weed suppressant has killed the weeds it can be stored away for later use and the ground can be dug and cultivated as normal.
DIGGING OUT COUCH GRASS
This won’t get rid of 100% of the weeds because some will inevitably be overlooked but if you keep an eye out for re-appearing weeds over the next month or so then they can easily be pulled out, mostly intact, from the freshly dug ground.
The downside is of course the effort involved but you need to consider that, whatever method you use, the ground will still need to be dug at some stage before planting crops or ornamental flowers. The extra effort of removing the couch grass roots during digging is, in our opinion vastly over-stated. You will also end up with soil of an excellent texture.
AMONGST OTHER PLANTS
Our suggested method is to first carefully cut away any grass foliage above ground. Then use a trowel to gently dig around the plants and remove as many grass roots as you can without damaging the roots of existing plants.
Finally and most importantly, then use weed-suppressant fabric or black plastic to cover the area. Cut holes or slits in the fabric to allow it to go around the stems of plants as near as possible. The weed-suppressant fabric can be left in place in place indefinitely because it is designed to allow rainfall to pass through to the soil below. Hold it in place (and disguise it) with a thin layer of soil.
If you use black plastic to cover the ground around plants be sure to pierce it in lots of places to allow moisture to sink into the ground below. This will inevitably allow grass stems to re-appear but they must then be removed by hand.
FACTS ABOUT COUCH GRASS
Below is a list of facts of facts about couch grass which are probably useless, but who knows, they may may open up a weak point in the growth cycle of this weed to you that others have not spotted.
- Elymus repens is a perennial plant with a lifespan that is limited only by surrounding conditions
- The roots are normally shallow but can go down as far as 20cm / 8in.
COMMENTS / QUESTIONS LEFT BY OUR READERS
|Date: 28 May 2016||From: Susan|
|The problem I find when trying to dig couch grass out of my allotment is that it is impossible to not take a significant amount of soil out at the same time as the grass and then how do you dispose of it?|
ANSWER: You have two real options. Firstly you can try and separate as much soil as possible from each clod as dig. If the soil is clay this can be difficult because the roots of couch grass will bring the soil together. I find that leaving it to dry, upturned, for a dry day does help significantly.
The second method is dig up each clod and place it, upside down in a heap. This will kill some of the couch grass over a moth or two but is not something I would recommend.
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Expert Advice on Getting Rid of Couch Grass Article by David Marks Couch grass (Latin name Elymus repens ) is a quick growing, invasive type of grass which appears to contribute nothing to the
A tall, very vigorous perennial grass with white, creeping underground rhizomes
- 1024px Kweek rizomen Elytrigia repens
Do you have Couch grass?
In the UK, there are five main species of perennial grass weeds of arable crops that are commonly known as couch or twitch. These are:
Elymus repens (= Elytrigia or Agropyron repens) – common couch. Very common throughout England and Wales, more scattered in Scotland. Occurs in a wide range of habitats, including field margins, hedgerows and rough grassland as well as arable fields. Up until the mid-1970s this was the most important weed of arable crops in the UK.
Agrostis gigantea – black bent. Widespread in England, but mainly on lighter soils than common couch. Probably under-recorded.
Agrostis stolonifera – creeping bent. Very common throughout the UK in a very wide range of habitats but less of a problem as an arable weed than common couch.
Arrhenatherum elatius var. bulbosum – onion couch. A variant of false oat-grass which is abundant throughout the UK in field margins, hedgerows, rough grassland and waste ground. The onion couch form has a much more restricted distribution as an arable weed, being largely confined to southern and central England.
Holcus mollis – creeping soft-grass. Widely distributed throughout the UK and occasionally a weed of arable land, usually on lighter, acidic soils.
Common couch (Shown in picture, via Wikipedia) is characterised by having creeping, white underground stems (rhizomes), shoots with small auricles and a short ligule at the base of the leaf blade. The heads (spikes) superficial resemble perennial rye-grass, but the spikelets sit flat against the stem rather than with the narrow, rounded side adjacent to the stem as in rye-grass.
Black bent also has rhizomes but has a long ligule, no auricles and the heads are large, loose panicles. Creeping bent is somewhat similar to black bent, although mature plants are shorter and produces creeping stems (stolons) on the soil surface, not underground rhizomes. Creeping soft-grass produces rhizomes, has conspicuously hairy nodes on the stem and a compact panicle.
Onion couch looks like false-oat grass with large loose panicles producing relatively large seeds with awns. However, the stem bases are swollen to form several round, onion-like corms, up to 1 cm in diameter, hence the common name.
Dense infestations of couch may produce several hundred heads/m 2 reducing cereal yields by 25% or more. High populations of plants can slow harvesting and the rhizomes interfere with cultivations and the harvesting of root crops by getting wrapped around equipment. Couch acts as an alternative host to the cereal take-all fungus which can have implications for the value of break crops in cereal rotations and take-all decline.
Why was couch a major problem in the UK?
In a survey published in 1910, couch was reported to be the most problematic weed of arable crops in the UK, just ahead of charlock. This situation continued right up until the mid-1970s due to the lack of effective herbicides and the limitations of cultivations as a means of control. This all changed with the introduction of glyphosate – a rare example of how a single highly effective herbicide can almost totally eliminate a major weed problem. Couch continues to be a problem on organic farms and in some perennial crops where it can be difficult to apply glyphosate without damaging the crop.
Agroecology – implications for control
- Couch grasses owe their success to their ability to spread by means of horizontal stems growing through the soil (rhizomes) or across the surface (stolons).
- These stem structures, which may extend to several metres, act as storage organs for food reserves. Buds and adventitious roots are located along the length of these at frequent intervals.
- The majority of the buds remain dormant unless plants are disturbed (e.g. by cultivation) when new aerial shoots or rhizomes will arise from many of them. In uncropped land, rhizomes growth is greatest from May to November, with peak growth in June and July, although this may be disrupted by cultivations.
- More couch plants arise from seeds than is generally supposed, especially with black bent, although the chief means of propagation in arable land is by means of the creeping rhizomes or stolons, fragments of which can produce new plants.
- Non-inversion tillage, and especially direct drilling, greatly encourages couch as there is less disturbance to rhizomes and stolons than occurs with deeper cultivations.
Management recommendations – herbicides
- In the UK, the introduction of glyphosate in autumn 1974 revolutionised the control of couch. Prior to that, the herbicides available were aminotriazole, atrazine, bromacil, chlorthiamid, dalapon, dichlobenil, EPTC, propyzamide, TCA and terbacil. None of these were as effective as glyphosate and most are no longer commercially available.
- Pre-harvest applications of glyphosate are approved for use in wheat, barley and oats, combining peas, field beans, oilseed rape and linseed. Applications must be made no less than 7 – 14 days pre-harvest, depending on crop. Control of couch pre-harvest is dependent on adequate green leaf and favourable conditions. If couch is senescing due to hot/dry conditions, control is likely to be reduced due to inadequate translocation to the rhizomes.
- The best control of onion couch is likely to be achieved by pre-harvest applications of glyphosate to earlier harvested crops, such as winter barley or oilseed rape, because it tends to senesce earlier than common couch.
- The most effective post-harvest technique is to leave stubble uncultivated and allow couch to grow to 4-5 leaves, typically 10 – 15 cm high, before spraying with 1.44 kg a.i./ha of glyphosate. Cultivating prior to spraying reduces overall control as new plants are likely to emerge post-spraying from damaged fragments of rhizome.
- Glyphosate is not very rainfast, and it is important that no rain falls for at least 6 hours, and preferably 24 hours, after spraying.
- Efficacy can be reduced by hard water so using a water conditioner can be helpful.
- Glyphosate is absorbed through the leaves and translocated to the rhizomes. To allow this to happen effectively, do not cultivate or drill for at least 5 days after spraying.
- Activity against couch is best when growing conditions are favourable – control is likely to be reduced if plants are wilting or cold or heat-stressed.
- Although glyphosate is highly effective against couch, it is slow acting and complete kill may take several weeks, especially in cooler conditions.
- Other herbicides that give selective control of couch within crops include propoxycarbazone-sodium (wheat) and propyzamide (various crops).
Only one case of evolved resistance to herbicides has been recorded in any species of couch worldwide – resistance to amitrole in creeping bent in pears in Belgium in 1986. Couch appears to have low risk of evolving herbicide-resistance – almost certainly because it is largely propagated vegetatively, rather than by seed.
Couch grass A tall, very vigorous perennial grass with white, creeping underground rhizomes 1024px Kweek rizomen Elytrigia repens Do you have Couch grass? Occurrence In the