Description: Couch (Cynodon dactylon) is a spreading, mat-forming, wiry-stemmed perennial grass with small, flat, soft leaves, stolons, rhizomes and a 3-7 fingered seed head with two rows of 1-3 mm long spikelets.
Life cycle: Couch is a perennial grass. It germinates from summer to autumn and flowers mainly in late winter to spring.
As a soil indicator: Couch is an indicator of very low calcium and phosphorus, high potassium, very high magnesium and iron, low humus in soil, compacted soils and low soil bacteria.
Beneficial attributes: Couch is an effective soil stabiliser.
Negative attributes: Couch forms dense patches that tend to exclude most other species. Even low levels of couch growth often lead to significant crop yield reductions due to direct competition for nitrogen and moisture. Dense stands can release allelopathic chemicals that reduce the germination and growth of other crops.
Dispersal: Couch spreads locally by creeping stems and spreads more widely via dispersion of stem fragments by cultivation.
Non-chemical control methods: Clean cultivating and slashing equipment thoroughly to reduce spread to clean areas especially from late spring to autumn.
Manual eradication of couch is very difficult, as all surface runners and underground rhizomes must be removed. Careful consideration is required when deciding which weed control tools to use. Poorly timed or poorly executed weed control practices may spread the weed. For example, a poorly timed mowing pass can encourage seed set, while a single cultivation pass with a rotary tiller can break up and spread the couch runners. Most growers use a combination of tools and take advantage of hot dry weather to increase the efficacy of their non-chemical weed control practices.
Grazing couch hard in autumn followed by hard grazing in late winter to spring can help to manage couch going into the growing season; however, additional non-chemical weed control practices need to be used during the growing season to maintain control.
Slasher®, an organic herbicide, can give good, short-term, knock-down control during the season when applied just as the heads of the couch start to emerge in spring, followed by a second application four weeks later. For the best results, Slasher® should be applied on a hot day, or before an extreme heat event, and applied in the morning, after the morning dew has dried.
Cultivation and cover crops
Growers are achieving good couch control by cultivating the couch and then establishing a competitive crop to suppress the couch. For the best results, cultivate the couch patches in autumn, before a stretch of hot days. High temperatures help to kill the exposed couch. If temperatures are mild, an application of Slasher® can be applied to mimic high temperatures.
An aggressive cultivating tool may be required to get under thick thatches of couch. A disc cultivator followed by a power harrow have been used effectively by some growers. The disc cultivator breaks up the soil and the power harrow pulls the couch up. A dodge plough is effective at pulling the couch out of the undervine area and into the mid-row.
The cultivated couch patches should be sown with a sufficiently competitive cover crop as soon as possible. Crops effective at suppressing couch are wheat, triticale, barley, oats, cereal rye, fodder radish, oil-seed mustard, canola, wallaby grass and creeping saltbush. When selecting a cover crop, it is important to consider the minimum rainfall required to support the crop and the growing habit of the crop. Tall growing crops are more suited to the mid-row area (Table 1); however, they can be used undervine provided a method is available to prevent them from growing into the vine canopy (e.g. undervine mowing, whipper snipping or sweeping).
Table 1. Cover crop options for the mid-row and undervine area of vineyards in different rainfall zones
|Area of the vineyard||500 mm||350 mm||250 mm|
Solarisation can provide reasonable couch control when the couch is completely covered with plastic sheets for 8-12 weeks in hot weather. After the plastic sheets are removed, regrowth can be controlled with either organic herbicide applications, multiple cultivation passes or a combination of cultivation and the establishment of a competitive cover crop. Henschke uses this technique but keeps the plastic in place for 2 years. This practice can hinder tractor access in narrow rows.
Growers’ experiences: Vasse Felix in Margaret River, WA controls patches of couch in vineyard mid-rows using cultivation and competitive cover crops. The weed-infested areas are cultivated with a disc cultivator to break up the soil, followed by a power harrow to pull up the weeds. The cultivated areas are sown with a green manure or pasture crop in autumn that competes with couch.
The best results are achieved when cultivation is timed to occur just before a stretch of really hot days. High temperatures help to kill the exposed couch. In cool conditions, Slasher® is applied to give the couch a knock before cultivation. This technique mimics the effect of hot weather and reduces the risk of the couch (or kikuyu) re-establishing. Options are being considered for establishing crops in the undervine areas to help keep the couch under control.
Gemtree in McLaren Flat, SA, has achieved excellent control of kikuyu (a weed similar to couch) by establishing an annual crop of cereal rye undervine, taking advantage of its allelopathic properties.
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