Unusual Turf Problems

Success with couch requires an understanding of its growing requirements, the removal of additional stresses and flexibility.

A damaged training area; couch needs to be ‘grown-in again’ following winter.

The arrival of spring will see couch (Cynodon sp.) starting to ‘green-up’ (break dormancy). Contrary to popular belief, couch is a weak plant during this time and good management is critical. Scheduling a cool-season type, spring renovation on couch can have far-reaching consequences on its performance.

Biology of couch

To appreciate its vulnerability during spring, it is necessary to understand the biology of couch. New Zealand’s summer (January–early March) provides a comparatively short growing season for couch. During this time, carbohydrate reserves are being stored
in the stolons and rhizomes to support the plant through the coming winter and subsequent spring.

Any problems at this time (such as shade from competing weeds or trees, incomplete cover, incorrect fertility or excessive wear) will limit the couch sward’s ability to rapidly re-establish full-cover in the subsequent spring.

To achieve sustainable, long-term couch performance in New Zealand, the aim should be for 100 days of active growth after the re-establishment of a full sward. Hence, full-cover must be achieved by early December, delivering couch sufficient time to produce and store adequate carbohydrates before growth slows in mid-March. If this timeframe isn’t achieved, eventual failure is unavoidable.

Winter dormancy

Winter dormancy occurs as night temperatures fall below 15°C (approx.). This accelerates where the couch is subjected to significant wear, as on sportsfields.

Spring green-up

The first growth occurs as soil temperatures at a depth of 100mm increase above 10°C
(approx.), when root activity commences. Then as soil temperatures rise above 16–17°C, the couch starts to break dormancy. This involves: Buds present at the nodes of the stolons and rhizomes growing new shoots. Shortly after the first signs of green-up, complete regeneration of the root system occurs.

The important point is that until green-up is fully achieved, the couch plant is completely reliant on its remaining carbohydrate reserves. Any additional stress prior to full green-up will further weaken the couch and delay both green-up and the opportunity to achieve full-cover before the next winter.

Factors affecting green-up

Factors affecting the speed of the green-up process need to be considered when putting together a spring management programme. These are summarised below:

Carbohydrate storage

The amount of carbohydrate stored the previous summer will generally be the main determinant of how readily the couch re-establishes full-cover during the subsequent spring. The best indicator of good carbohydrate levels is a lot of thick, underground rhizomes – the deeper the better.

Rhizome development tends to follow stolon development, which is why the length of the growing season is so important. The initial phase of growth is for stolons to colonise bare ground. Only after full-cover is achieved can rhizome growth and, hence, carbohydrate storage occur.

Drainage

Poorly-drained sites mean a late green-up (and hence, a shorter growing season) because: nnWet soils are slower to warm up in spring. nnSoil oxygen levels (critical for the green-up process) are typically very low. nnPoor drainage inevitably results in the demise of at least some of the rhizomes, depleting available ‘food reserves’.

Thatch

Thatch does provide some insulating benefits. But excessive thatch in our climate is considered detrimental because of the surplus moisture held at the surface. It further delays the warming of the soil in spring.

Shade

For those growing couch on golf courses and home lawn situations, shade is often a major issue. It delays the warming of the soil and lessens the vigour of growing plants.

Seasonal variation

Seasonal variation from one year to the next is a major challenge when growing couch in a marginal climate such as New Zealand’s. Each year can be (and often is) very different. The spring of 2012 was wet and cold – delaying initial green-up, re-establishment of full-cover and the start of the carbohydrate storage phase. Fortunately there followed a particularly hot, dry summer to compensate. The key message here is that a rollover, calendar-based programme isn’t
always appropriate. When managing couch in a marginal climate, current conditions must be considered and the programme adjusted accordingly.

Maturity

Too often with couch, maturity is considered in terms of the time since it was planted (e.g. stolonising occurred 6 months ago), rather than the amount of active growth that’s been possible. This difference is critical. Late plantings (February onwards) result in essentially immature plants being treated in the following spring, as if they are fully mature. Immature couch is less able to tolerate the stresses of top-dressing, herbicides and thatch control. It needs to become fully established first.

Wear

The level of wear and damage is another important consideration. A complete and mature sportsfield cover at the start of the winter playing season is often severely damaged by season’s end. The above-ground stolons are worn away completely and so, in many cases, you are back to dealing with an immature plant. Once again, a grow-in strategy is initially required.

Remember that the state of sportsfields will be quite different to that of golf fairways. The intensity of wear on a fairway is low, and so the bulk of the above-ground stolons survive the winter. In that case, a quicker green-up and re-establishment of full-cover results. The intensive wear on sportsfields annihilates the above-ground stolons, so recovery has to be from below-ground rhizomes. If there are no rhizomes, you are in real trouble. Even if there are some, recovery will be slower as the rhizomes have to commence growth, form stolons and then re-cover the bare ground. On heavily-worn areas of sportsfields, full-cover may not be re-established until early autumn (if at all).

Spring management

The key to successful spring management of couch is to avoid applying any unnecessary stress to the turf until complete green-up is achieved and full couch cover is re-established.

Fertility

At the first signs of green-up, monthly applications (approx.) of either a NK or NPK fertiliser are recommended. Care is required to not apply too much nitrogen (i.e. no more than 10–15kg actual nitrogen/ha/application) until full green-up is achieved, as it can be counterproductive.

Once there’s full green-up, mainly fertilise with nitrogen as required until full-cover is achieved.

Herbicides

The challenge with herbicides (grass and broadleaf) is that the whole area is normally treated. Unless catastrophic damage occurs, any negative effect on the couch is generally not recognised or is attributed to something else, i.e. the weather.

The reality is that most herbicides impact on couch growth to some degree. When the couch is greening-up, new shoots from dormant buds can be easily damaged and even killed by herbicide applications. At other times of the year, they would have no detrimental effect.

Poorly-timed herbicide applications to a couch sward with minimal carbohydrate reserves from the previous summer can have a catastrophic effect, including the death of much of the sward. They can also delay green-up and the re-establishment of full couch cover by many weeks. The rules of thumb when applying herbicides to couch are:

  1. Control of both grass and broadleaf weeds needs to be completed prior to couch re-growth commencing in the late winter/early spring. Unless a dual ryegrass/couch sward is maintained (see below), the best option is to keep the surface clean of weeds all winter, with herbicides applied sooner rather than later.
  2. Once re-growth starts (from early August onwards in Auckland), the use of herbicides should be delayed until full green-up is achieved. To be safe, wait until at least mid-November.
  3. As mentioned earlier, consider the maturity of the couch. Young plants are more sensitive to herbicides (and certain products simply shouldn’t be used at all).

Renovation

For cool-season grasses (e.g. ryegrass or browntop), it is normal to complete renovation during spring (late August–early October). The same doesn’t apply to couch. Heavy top-dressing (sand or soil) or de-thatching in spring will further delay the establishment of full-cover. Renovations need to be delayed until December, at the earliest, when there’s full-cover and the couch is actively growing. At that stage, rapid recovery will occur.

Irrigation

Couch is a warm-season grass and is capable of withstanding a dry environment. Assuming you are not trying to establish new stolons, it is particularly important during late spring (when the first dry weather is likely to occur) that a judicious approach to irrigation is adopted.

Over-watering results in a saturated root-zone, which impedes the spreading of the couch. This delays the re-establishment of complete cover.

Competition from weeds needs to be managed before couch starts to green-up.  Photo provided by Omanu Golf Club.

Dual cultures (ryegrass/couch)

In some sportsfield situations, it is normal to oversow couch with ryegrass during the late summer, in preparation for winter.
The ryegrass is then removed – prior to green-up starting or once green-up is completed.

The results of two research projects on the timing options were previously reported in the Turf Management Journal (November 2012).

Conclusion

When growing couch in a marginal climate, Turf Managers need to understand and respect constraints imposed on the plant.
It is essential to recognise that couch is vulnerable during the spring green-up and re-growth phase. At that time, it is best to leave well alone. Definitely provide it with fertiliser, as required, for re-growth but avoid any treatments that place additional stress on the couch.

References

Beard J.B. (1973) “Turfgrass Science and Culture”.

McAuliffe K. “Overseeding into Warm Season Grasses”, November 2012 NZ Turf Management Journal, pg 12–14.

Glasgow A. “Transition Trial at Silverdale Rugby Club”, November 2012 NZ Turf Management Journal, pg 16–17.

David Ormsby

David Ormsby

Agronomist

New Zealand Sports Turf Institute

Alex Glasgow

Alex Glasgow

Agronomist

New Zealand Sports Turf Institute