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A Pitch Battle - Waging War on Poa Annua

By Carl Pass
Managing Director - Premier Pitches Ltd


Sometime ago I wrote an article entitled the Dutch Revolution that looked at the then, relatively new concept of the Koro range of machinery developed in Holland. Within the article I predicted that the Field Top Maker would become a regular part of our armoury of machinery used in the battle to, one day, produce the perfect natural turf pitch. This was followed up by a further article looking at the new set of problems faced by league groundsmen and how best to address them by using the Koro range of machinery as part of an integrated management programme.

Time has now passed and we have had the chance to assess the effects of the 'Dutch Revolution'. There is now the generic term used by some in our vocabulary, 'Koroing' which describes the use of the Field Top Maker. It should be noted that the Field Top Maker is only one of a range of machines available from the company. The FTM and other machines have all been designed to work in harmony in different situations.

As with any new concept or idea, things need time to develop and evolve, people are by nature cautious and often reluctant to change their ways and methods. This has been the case with the Koro range of machinery. Whilst the more progressive consultants and groundsmen saw the potential immediately others chose to monitor the situation to see how it progressed. I would suggest that those who undertook work using the Koro Field Top Maker have not regretted the decision, on the whole if the work was undertaken correctly a high percentage of Poa Annua and all associated thatch will have been eradicated from their swards.

Now we have experience of the use of this machine, particularly in stadium environments, we can better understand its effects and the results of its use. As such I would like to look at some of the effects which need to be addressed if sports turf mangers are to fully understand the impact of its application.

Reduction in thatch and Poa Annua

Many will now be familiar with the term frase mowing which describes using the Field Top Maker to remove organic debris and shallow rooted Poa Annua leaving the Rye Grass plants roots and growing eye intact. Fraise mowing, in its pure form, can only be achieved if a sward is dominated by Perennial Rye Grass. Pitches, which have not been subjected to the use of the FTM and are heavily infested with thatch and Poa Annua, will not successfully frase mow. In the first instant these pitches will require what could be described as fraise topping. Fraise topping refers to the total removal of all herbage and a degree of the existing soil. Once fraise topping is complete the pitch will be in a similar condition to a newly re-surfaced pitch which can then be renovated using whatever method is preferred. The vital point is that a new Rye Grass sward can then be established with a much-reduced amount of Poa Annua and no thatch. True frase mowing can only be undertaken on a pitch that has, either been resurfaced in the previous year or has been fraise topped.

Fraise mowing when achievable will leave the surface devoid of thatch and Poa Annua also any small surface irregularities will be largely removed during the process. One area that appears to cause concern amongst some turf managers is the amount of material that is physically removed during the operation. Whilst, to my knowledge, no data exists, experience suggests that the total amount is far less than it first appears. The main part of the bulk removed is in fact unwanted material comprising of leaf tissue and organic accumulations. Some soil is inevitably lost during the process, which is in real terms negligible and can be replaced by top dressing if required. Within this debris a percentage of Poa Annua seeds will be removed for disposal and they will not have the opportunity to re-establish on the playing surface.

When fraise mowing is complete there will be a visible light coloured tinge throughout the surface. This is the top of the Perennial Rye Grass plants which will, within a couple of days, start to turn green as the plant produces new fresh leaves from the root stock still in place within the soil.

Prior to the introduction of the FTM Groundsmen who wished to reduce thatch and Poa Annua were limited to the use of scarifyers during end of season renovation. As a contractor I have been involved previously in scarification operations which lasted for several days as we tried to strip a soccer pitch to make it as clean as possible, prior to other normal end of season operations commencing. During which time several sets of belts and numerous tines ended up on the scrap heap. Given that, apart from resurfacing, this was the only technology available at the time as a control against thatch and Poa Annua, I still had my doubts as to whether we were in fact reducing the thatch but at the same time encouraging the re-establishment of Poa Annua. Correct use of the FTM defiantly cleans out a far higher percentage of Poa Annua and removes all thatch and organic debris. However, noticeably in the stadium environment, some Poa Annua does manage to gain a foothold, which is not unexpected given the nature of the plant and its determination to survive.

Keeping Poa Annua at bay

Particularly in the stadium environment one theory suggests that soil bound Poa Annua seeds are present in sufficiently large numbers to re establish after "Koroing". This is to say that a seed bank is present within the soil which when exposed will regenerate and Poa Annua will start to colonise. When I first visited Rotterdam to see the results of work undertaken by the machines inventor Ko Rodenburg I was amazed at how little Poa Annua existed within the swards of the pitches which had been subjected to Koro Field Top Maker operations. After working with the machine in this country on heavily infested Poa Annua pitches it became apparent that one of the reasons for the purity of sward in Holland was that the operations had been carried out over a period of several seasons. This I believe has reduced the seed bank of Poa Annua by diminishing returns, to levels that do not cause further large-scale infestations.

Having spoken to several people who have used the Field Top Maker to good effect, swards have returned to Perennial Rye Grass and the pitches they are responsible for have outperformed the slow spongy Poa Annua pitches previously seen. However some are of the opinion that now they have established a superior pitch they do not need to employ the FTM at the end of this season and wish to return to the more conventional methods. Choosing to scarify as we did in the past is, in my opinion, not an option. The resultant clean open ryegrass swards seen in Holland and now at some venues in the UK are a consequence of the routine use of the Field Top Maker over a number of years. If we are to achieve the same results the FTM must be used routinely on an annual basis.

Adapting to change

One of the major benefits in using the FTM is that we can now produce pitches which are not prone to divotting out. Replacing divots takes up valuable man-hours that could be better spent on more productive aspects of sports turf management. Scarring does occur which is to be expected on a natural turf surface, scarring however has little effect on the balls ability to travel without deviation and can be repaired with far less effort.

What has been noticeable since the introduction of the FTM is that the amount of fertiliser required to sustain a sward is higher than that previously required, as is the case with first year resurfaced pitches due to the eradication of thatch. Previously pitches with thatchy organic accumulations would by nature hold on to a degree of nutrient within the top 20mm. This in turn leads to a proliferation of Poa Annua which, flourishes under such circumstances by thriving on the nutrients retained within the thatch layer.

Restricting fungal disease

Some groundsmen have recorded higher amounts of fungal leaf spot within their new swards. Rye Grass swards can be vulnerable to leaf spot attacks particularly when immature. This disease can be encouraged when the plants nutrient levels become diminished therefore regular applications of Nitrogen and Potassium are essential to maintain nutrient levels. Fortunately Fusarium appears not to be a problem in the new clean Rye Grass swards. This disease found an ideal home in soft thatchy Poa Annua swards where conditions were ideal for it to flourish and reproduce causing irreparable damage. The solution to keeping Fusarium at bay is expensive, repeated applications of fungicide could ultimately lead to depletion in beneficial fungi as well as those responsible for Fusarium.

Surface Hygiene

Surface hygiene in the form of scarification, verti cutting and sweeper collection all have a place in the production of a high quality playing surface. These operations should be employed once a sward has been established after being cleaned out by the FTM rather than as was previously the case at the renovation stage. It is essential to undertake such operations to keep the sward upright and open. If a proportion of Poa Annua still exists within the sward, sound surface hygiene practices will prevent it from attaining its natural procumbent habit, which if left unattended will eventually lead to the production of thatch. Another advantage in keeping the sward upright is that Poa Annua plants will be lifted. When flowering the florescence will be removed by mowing before they turn to seed thus preventing the plants reproducing.


To summarise, we are now starting to appreciate what is involved in keeping Poa Annua at bay within the stadium environment, using cultural practices. End of season renovation should not be carried out without firstly either resurfacing, frase topping or, in the case of pitches which have already been subject to one or the other during the previous year, frase mowing. This can then be followed up by whatever is required to renovate the pitch. Attention given to surface hygiene during the growing months will assist in keeping the sward open and healthy.

The aim of any winter games groundsman is to produce a pitch that will be in the best possible condition during the key months of winter - we now have more of a chance than ever to achieve this.

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