The Disturbance Theory - Do Not Disturb!

The Disturbance Theory - Do Not Disturb! Richard Windows, STRI Turfgrass Agronomist.

I would like to thank Richard Windows for permission to translate into German. February 25, 2017 Norbert Lischka

Perennial grasses such as Festuca and Agrostis Capillaris require some time to establish. Richard Windows describes this in a really great article. Apparently most of the examples in his article are based on Links Open Championship courses. This data and the specified parameters cannot be transferred 1:1 to other places. Most of the time, however, the principle of low disturbance for the successful establishment of Festuca and/or Agrostis species remains unchanged. Before using the Disturbance Theory, any problems with thatch, black layer, algae, moss, layering, drainage and compaction in the turf base must first be eliminated.

Greens with a high proportion of Agrostis and Festcua grasses generally ensure consistent putting surfaces all year round. Unfortunately, however, many of our greens continue to be dominated by the annual Poa Annua. A survey carried out by all STRI agronomists in the UK and Ireland for the R&A (Research and Analysis) proves this. The average species composition of golf greens in 2005 was 56% Poa annua, 32% Agrostis, 7% Festuca, and 5% ryegrass. On 598 courses examined, 75% of the greens showed more than 50% Poa Annua. This dominance of Poa Annua makes our greens vulnerable and inferior in winter. This information shows how many places are not living up to their potential.

In the past, the main reason for Poa Annua's dominance was always attributed to the use of too much fertilizer and water. I used to think the same way until I looked at the ecology of grasses. The article “Changing the Nature of Your Greens” explains this in detail. In summary, Poa Annua benefits from disturbance, while the finer grasses (Agrostis Capilaris / Festuca) are more comfortable in a quiet environment. Poa Annua is so successful in golf greens because the environment (putting surface) is constantly being disturbed or damaged. The pressure to disrupt is caused by the surface treatment and of course by the game. In this article we examine the influence of surface care on the composition of grasses. The goal is to help you think about caring for your greens a little differently.

The real cause of Poa Annua's spread is creating gaps in the lawn. Constant physical damage (or disturbance) to the grass plant causes these open spaces. Modern greenkeeping practices and mechanization have radically increased the disturbance pressure placed on fine turf. We mow, groom and scarify too often to please the increasingly demanding modern golfer. While such aggressive practices may be undertaken for the right reasons, they could end up causing untold harm. Symptoms become visible when the lawn thins and the soil surface becomes exposed. Poa Annua is particularly adapted to these conditions. It may therefore be true to say that the incorrect use of the triplex mower and other modern machines and tools is one of the main reasons for the dominance of Poa Annua in our golf greens.

Before we had these extremely efficient tools, the amount of maintenance on our greens was limited by time and the physical limitations of the human body. It took a long time to mow the greens with a push mower, a push mower or even a scythe. Not to mention the physically demanding nature of the work. At that time it was therefore almost impossible to put too much strain on and disturb greens. As a result, the green and golf green surroundings were mostly undisturbed, allowing the fine grasses to dominate. Fertilization and irrigation were reduced to a minimum, otherwise the grass would simply grow faster! The greenkeepers already knew back then that rapid growth would make the putting surface inferior. Growth was the last thing they wanted. A stable, undisturbed and unproductive environment is better suited to the finer grasses. It also offers the best putting surfaces all year round. Old Tom Morris understood that.

The tranquility of this undisturbed and unproductive environment was forever gone in 1968 with the introduction of the Triplex lawnmower. Suddenly the greens could be mowed in a fraction of the time, and this was now done even more regularly. Greens were mowed even when it wasn't necessary! Further technological advances even allowed it to follow contours, which made tighter mowing in curves easier. Essentially, triplex mowing increased pressure on the lawn.

Shortly after the triplex mower, other powerful and effective machines for lawn cultivation were introduced. These machines, with their motor-driven steel blades (nowadays tungsten-tipped), were much more aggressive than the bristles of a brush - you could just imagine Festuca and Agrostis trembling at the prospect! The ease and effectiveness of the machines' use caused the frequency with which they were used to increase. The result was increased disturbance pressure on the turf.

The use of the triplex mower as well as more efficient tillage machines gave golfers the faster putting surfaces they demanded. However, little attention was paid to the damaging effect on the fine grasses. To put it simply, the delicate Festuca and Agrostis Capilaris grasses could not cope with the damage. Consequently, the grass began to thin out. Gaps now emerged that were exploited by the Poa Annua - the invasion had begun. In order to help the now thinned and weakened grasses regenerate, more fertilization and watering was carried out. Poa Annua now thrived in this disturbed and more productive environment. The fine grasses decreased significantly and many of the putting surfaces would never be the same again. The era of aggressive care and heavy doses of fertilizer and water had arrived (to our shame).

Some greenkeepers ignored the trend toward aggressive surface care. They knew this wouldn't make their surfaces any better. To this day, the golf courses that have the best putting surfaces are those that have upheld these strict principles. The greenkeepers with this care management followed what Old Tom had done all these years. They know that the slow-growing, fine grasses only require gentle care to produce high quality on the surface. If modern care machines are used, then only with great caution. For example, scarification is rarely carried out, and then only when the fine grasses are growing strongly. There is never any clear-cutting on the greens. Fertilization and water are always kept to a minimum - because too much of it only requires even more aggressive care. Therefore, these areas remain consolidated and unproductive, and that is the reason why the fine grasses continue to develop very well. Old Tom Morris taught us this approach. Today we call this “traditional greenkeeping.”

The results of traditional greenkeeping were once again particularly evident when the Open Championship was held on the Old Course at St. Andrews in 2005. During the championship the greens were left at 4.5mm. Mowing was omitted unless it was necessary - the slow-growing, fine grasses simply did not need to be mowed every day. Light brushing, light topdressing, a bit of rolling and dethatching before the tournament was enough to achieve over 10.5 feet on the stimpmeter as well as provide smooth and true ball travel for the best players in the world. Compare that to normal maintenance for other major tournaments. There the greens are almost scalped two or three times a day! It's obvious what kind of grass you're promoting.

Perhaps I have been a little unfair in blaming triplex lawnmowers and modern maintenance machines for this scenario, because of course they were major innovations and have improved the quality and efficiency of lawn production. Of course, the problem is not with the machines, but with the way we use them. All too often they are used too frequently and too aggressively. However, such incorrect use increases the disturbance to the lawns. If the pressure becomes too great, the lawn will thin out and gaps will appear and Poa Annua will take hold. In order for the lawn to recover from this pressure, it requires a careful hand when fertilizing and watering. It is this combination of disturbance and higher grass productivity that then leads to the undesirable dominance of Poa Annua.

I have no doubt that better putting surfaces can be achieved by encouraging the finer grasses. To be successful, we must adapt our care practices to minimize disruption and reduce productivity. Essentially, the way we work surfaces needs to become less aggressive. This is not very difficult to achieve, let me describe a few simple strategies...

• Reduce mowing frequencies. Ask yourself – do you really need to mow all the time? Can you skip occasional mowing sessions?

• Raise cutting heights. Every greenkeeper knows what cutting height is comfortable and stress-free for his lawn. You should not go below this height. Avoid going over the edge of your lawn as it will not be able to cope easily.

• Simply skip the final round every 2 or 3 days. The first symptoms of excessive disturbance are first seen on the final round of the greens (Triplex Ring). Do not groom or scarify this area.

• Avoid dethatching and scarifying. Consider brushing or light grooming (brush broomer) to gently refine the lawn. If dethatching or scarifying is necessary, ensure that the finer grasses are growing well at this time. For a quick recovery, support this with reseeding to promote the complete restoration of the turf. Under no circumstances use metal groomers or scarifiers when the Poa Annua is in flower.

• Increase top dressing frequencies to achieve smooth and firm putting surfaces as well as thin out the felt. Avoid harsh maintenance measures to drag the sand on the surface, this will harm your lawn.
• Use a roller or iron to provide a little extra speed and smoothness if needed. This ensures that the greens can be maintained at a higher cutting height.
• Mow more often by hand instead of with triplex mowers, it causes less disruption and also allows you to check your lawns better.

The real reason Poa Annua invaded our fine lawn surfaces was the formation of gaps in the lawn. Aggressive surface care was one way to allow such gaps to appear. Excessive input of water and fertilizer were used to repair this damage. This resulted in a productive and highly disturbed environment in which Poa Annua thrived and dominated. The current era of aggressive high input (fertilizer/water) in greenkeeping promotes exactly these unwanted species. To restore the dominance of the finer grasses, we need to create a balance and a less productive environment. To do this we need to prepare our surfaces differently, but not at the expense of the quality of play. The key to this strategy is minimizing disruption. This means less aggressive surface care through careful use of triplex lawn mowers and modern maintenance machines. You will notice that with this approach the fine grasses will return to your greens.

The incorrect use of automatic irrigation is another reason for the decline of finer grasses on British and European golf courses over the last 40 years. This, coupled with the invention of triplex mowers and compound fertilizers in all their forms, is a disaster for the Agrostis Capillaris / Festuca grasses. The creation of softer and more lush growing lawns made the game easier and more suitable for the TV networks, which now broadcast extremely ultra-green images into our living rooms. The age of “deified greenery” had arrived, and everything agronomic was quickly forgotten, only to drown in a sea of Poa Annua.

So how can we set about correcting the mistakes and creating the best environment for the preferred grasses? Well, the tool that was partly responsible for the decline could now be the salvation. Irrigation is the most powerful agronomic tool as long as it is used correctly.

The article "Changing the Condition of Your Greens" made the claim that unnecessary disturbance is the main reason the fine grasses are disappearing from our golf courses. We have inadvertently created an environment more conducive to adapted grasses like Poa Annua: we fertilize and water, which means we then have to use aggressive maintenance to create reasonable playing areas. The finer grasses simply cannot handle this intense disturbance, while Poa Annua likes nothing better.

Greenkeeping requires a basic knowledge of the ecological strategies of the two or three most important grasses. Success will come if we create the right environment for the finer grasses. In summary, the fine Agrostis and Festuca grasses prefer a solid and unproductive environment, while Poa Annua dominates when productivity and disturbance pressure are particularly high. By understanding these ecological strategies, we can easily reverse the plant decline on putting surfaces that we have experienced over the past 50 years. We need to move away from high inputs (fertilizer/water) and aggressive greenkeeping practices. One of the most important tools in this process is the correct use of irrigation. Believe me, if we get this right, the finer grasses will return and we will restore the true enjoyment of real golf.

Let's consider two scenarios. The first is a surface dominated by annual bluegrass. This has been over-fertilized and over-watered for years, sometimes with 5 cm of thatch in the upper half of the turf base layer. The putting surfaces in summer are usually satisfactory, but in winter the surfaces are soft and prone to disease. To improve lawn quality, we need to reduce the productivity of the environment, which we achieve by minimizing irrigation and fertilizers. At the same time, we need to create the right soil conditions by reducing thatch so that the fine grasses can thrive. This improves the strength of the area and reduces the need for excessive disturbance, which in turn creates a quieter environment. If productivity is reduced, it should be done through a gradual approach, because a radical change in the amount of irrigation or fertilizer will unduly affect the quality of the game.

The second scenario is a lawn where both Agrostis Capillaris and Festuca grasses are dominant and there is only a low contamination of Poa Annua. The goal here is to maintain the dominance of the fine grasses. We do this by exerting controlled pressure on the weak roots of the Poa Annua by heavily regulating the amount of irrigation to prevent them from spreading. To achieve this goal, we have even more opportunities to play with irrigation effects in late summer. This allows us to further reduce the resistance of the Poa Annua before reseeding with Agrostis Capilaris / Festuca grasses.

In both scenarios the aim is to create a more stable and as unproductive environment as possible. Irrigation should be limited at the appropriate time in order to exert the necessary pressure on the shallow growing roots of the Poa Annua and thus reduce resistance. As the proportion of fine grass components increases, greater stress can be applied as the lawn's water requirements naturally decrease.

Proper irrigation is ultimately crucial for the cultivation of fine lawns. We use them to promote the strengths of the deep-rooted fine grasses and to exploit the weaknesses of the shallow-rooted annual bluegrass. If the use of irrigation is correct, the dominance of the fine grasses will be restored, providing us with golf surfaces that are befitting the heritage of the game. The extent to which irrigation is applied is of course the biggest challenge. Water requirements decrease as we optimize quantities and maximize water permeability. In today's world it is important that the water is fully used by the lawn and not wasted. But how much or how little do we spend now? Well, that's the 64,000 euro question. I don't think this can be taught theoretically. Every area is different, every green is different and every square meter of lawn is different. Attempting to empirically measure these differences and then offer a general solution is illusory. Attempting to implement this concept will most likely result in a further decline in turf quality. There is no doubt that effective irrigation is an art, not a science. However, there is one governing principle - water should only be used to keep the lawn alive and the surface even - nothing else!

Successful irrigation management can only be achieved if greenkeepers draw the right conclusions. There is no substitute for a good man with in-depth knowledge of his golf course. The person in charge should know much better than any computer or tensiometer how much water is needed to keep the turf alive, facilitate agronomic improvement and optimize playing quality. If we want to restore the proportion of fine grass on our greens, golfers must trust the judgment of greenkeepers.

Watering doesn't just mean simply pressing the button on the automatic system. This approach will lead to general agronomic deterioration. We need to create a healthy dry area rather than one that is too lush and dynamic. To help with this, we need to ensure that the water we apply can penetrate the soil. This is achieved through the use of wetting agents combined with regular ventilation measures. Additionally, many clubs have had great success with water injection ventilation using Hydroject. Not only is the soil aerated, the deeper-rooted fine grasses are also better supplied with water, which gives them a greater competitive advantage over the shallower-rooted Poa Annua.

Today's irrigation systems are great and sophisticated tools, but they are also a disaster if they fall into the wrong hands. There were too many wrong hands at work that caused the decline of the fine grass on our pitches over the last forty years. We have a duty to correct this and restore the connection between the grass we play on and the game itself. Our golfing heritage depends in large part on proper irrigation.

It's not what you think

In times of healthy debate, consider this thought...
... You shouldn't let your lawn starve in order to encourage the development of the finer grasses.

To favor the finer grasses, fertilizing is more about not over-fertilizing than adopting a starvation strategy. The goal of this article is to help you develop a formula for your fertilizer program that keeps the needs of the finer grasses in mind. With a predominance of Agrostis Capillaris / Festuca we can achieve a better quality of the surface all year round.

The downward spiral

The problem is that too much fertilizer forces you to scarify intensively and mow aggressively to prepare firm, fast and regular playing surfaces. This means that aeration with hollow spoons and deep scarification are necessary to get rid of the thatch in the deeper layers. But it is this constant damage that the finer grasses cannot survive. Such an aggressive method of creating putting surfaces inevitably leads to further fertilizer applications to allow the turf to recover from the attacks. The constant disturbance coupled with high productivity leads to the dominance of annual bluegrass.

That's it

We try to minimize fertilizer inputs to reduce the need for disturbance. A firmer and less intensively maintained environment will give Agrostis Capillaris / Festuca a fair chance. A less disturbed environment allows a little stress to be placed on the annual bluegrass. Let me say something about fertilizing golf greens that favors the finer grasses.

We take a step back and think

Our goal in greenkeeping is to create playing surfaces of the highest possible quality. If that means we want to encourage dominance of the finer grasses, we need to have the right environment. In order to ultimately minimize the degree of disruption, we must reduce fertilizer inputs. At some point during the summer at the time of reseeding, we then beneficially apply stress to the annual bluegrass to give the finer grasses an advantage. We offset this burden with judicious irrigation rather than fertilization because it is easier to control. Generally we try to keep irrigation applications to a minimum to prevent thatch buildup, but we only use this to apply pressure for a short period of time. This will serve to weaken the annual bluegrass before the new seeds emerge. Too much stress for too long weakens all types of grasses, and golf greens are put under too much stress to be weak. See “Changing the Texture of Your Greens” for more details.

Just enough

So we want to minimize fertilizer inputs to reduce the need for incessant aggressive measures. Minimal (some would say "optimal") means providing just enough growth on the putting surface to prepare it and endure play without being destroyed. The desired level of growth will vary depending on what we want to achieve at different times of the year. In spring, for example, we need to generate a certain level of growth to ensure recovery from winter damage, as well as to enable early preparation for the season. In summer, when we have our surfaces well set up, we want quiet growth so that we have to carry out as little aggressive maintenance as possible. In the fall, we need to make sure the turf is strong enough to recover from end-of-season repairs before winter dormancy begins. Now, when minimizing fertilizer input, focus on sensitivity and timing. In the past, fertilization was done by hand to leave out limited areas or to apply extra nutrients depending on the lawn conditions - now that's finesse! Essentially, you only need to fertilize where necessary and no more.


With regard to nitrogen fertilization, experience in Denmark with greens built close to the ground considers 5-7 g N / m2 per year to be sufficient. You should apply as little as necessary so that you don't have to scarify too often over the summer. Be careful weaning greens with high N fertilization, this can also lead to negative consequences in the form of diseases. Regularity and confidence in judgment, that's all.

In most cases, the main source of nitrogen should be ammonium sulfate to achieve an acidification effect. The finer grasses can tolerate a pH below 5.5, while Poa Annua cannot. Nutrient availability and microbial activity are factors that are not the focus of this article. In general, the annual bluegrass can be selected by lowering the pH value. Therefore, around 75% of the total nitrogen should consist of ammonium sulfate.

The remaining nitrogen (25%) can be compensated for with small liquid amounts of urea base during the summer months. Do not use too much organic nitrogen and/or nitrate as this will only increase susceptibility to disease through lush growth. Disease equals disorder and therefore plays into the hands of the annual bluegrass. Just try to minimize nitrogen inputs, which will reduce the need for disturbance.

Festuca can thrive at high pH, but Poa Annua dominance can only be avoided by an overarching environmental stress, such as increased salinity or drought. Weeds, worms and diseases generally benefit from liming.


The research results on the influence of phosphate applications on the quality of fine lawn grasses are contradictory. Constant application of phosphate fertilizers undoubtedly promotes the development of annual meadow grasses, but this connection has not been clearly proven with lower doses. Regular phosphate doses create ideal conditions for seed germination, to the benefit of Poa Annua. Keep cool and remember that phosphates are usually not necessary to benefit Agrostis Capilaris and Festuca.
I think that the well-known problem of spots literally “burnt” by rabbit urine should be interpreted as meaning that burns are more likely to be associated with urea-containing fertilizers - only to lead to an invasion of annual bluegrass - and not a direct result of high phosphate -Gifts are.


Potassium is more mobile and may be necessary as a supplement on sandy soils. Certainly potassium has drought and disease tolerance benefits, but don't pin all your hopes on it. Monitor potash levels annually if there is any doubt. Remember that favoring the finer grasses depends on minimizing disturbance.

Keep it simple

So what does this mean in terms of your fertilization program? For example, you could stimulate growth in the spring by fertilizing with Lawn Sand. This should be applied at the start of spring growth and will lead to recovery from winter damage. An application of 8:0:0 or 8:0:6 could be applied when growth has started strongly in the spring. This growth allows for early season preparations. Using an ammonium sulphate-based fertilizer in spring will prevent the Poa Annua from settling in the gaps in the lawn by lowering the surface pH value. Liquid fertilizers can then be applied occasionally during the summer months to keep the grasses healthy rather than to encourage lush growth. Seaweed can be used in a mixture with other liquid fertilizers if you feel this will have a positive effect. In order to strengthen growth in autumn and harden the lawn against disease, we recommend using a lawn hardener (2-0-2 3-0-3 Fe or similar) as a final step. The amount of application should be as small as necessary. Your fertilization program should focus on controlled growth so you can avoid aggressive surface care.

Surface care

But how do we prepare the surfaces without incessant scarifying or ever lower cutting heights? With spring growth, they start with strong top dressing to strengthen and prepare the surfaces. Scarifying may be necessary from time to time during this time, but not excessively or too often. Once the surfaces are prepared, we should aim to leave them alone. We maintain our firm, consistent and smooth surfaces without excessive growth through brushing, light top dressing, rolling, reasonable cutting heights and, if necessary, individual light scarifying.

Regular top dressing has the added benefit of keeping the lawn soil sandy and unattractive for Poa Annua seed germination.

Less is more

If you want to fertilize the soil for the finer grasses, you should keep an eye on minimizing aggressive surface treatments. You will need strong growth in the spring to prepare your surfaces, but then you should go with nature. Your job is to find the lowest possible growth level that maintains surface quality without incessant scarifying. Ask your fertilizer supplier to focus on this when making recommendations based on soil analysis results.

The fine grasses are tender souls, they don't like rough treatment, but they can withstand stress. We put stress on the annual bluegrass for a limited time in the summer by allowing it to dry out in a controlled manner and at the same time reseeding to give the seedlings the opportunity to establish themselves. Be patient and stick to your principles and the fine grass will come.

Keep this thought in your mind...

... Aggressive greenkeeping is the death of fine grass.

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