Controlling Thatch

Controlling Thatch

By Laurence Gale MSc

Keeping things in moderation is the key to success in most aspects of life - thatch is no different.

There are some characteristics of thatch that can be good for turf surfaces in certain situations. Thatch can provide a resilient cushion for some sports surfaces or can help provide some insulation and retain moisture, particularly useful in sand predominant surfaces. In the main thatch only becomes a problem when it is left and allowed to accumulate in the turf surface.

Thatch is a problem because the natural process of breaking down organic matter (OM ) living and dead stem/root tissue materials is often very slow. Invariably, because we are promoting vigorous grass growth, we end up increasing the problem. The plant produces more debris than it can break down, thus we get an accumulation of material which, over time, builds up into a thatch layer.

Thatch becomes a problem for groundsmen when it exceeds 10 mm. This accumulation of thatch can create an environment that affects sward quality in many ways:

• Excessive thatch can create a favourable environment for many pests and diseases.

• Thatch can influence water movement in and around the grass plant.

• Thatch can alter soil surface conditions, often producing a waxy layer that can prevent water movement into soils (dry patch).

• Thatch can influence soil temperatures.

• Thatch interferes with air movement around the grass plant.

• Thatch can affect mowing quality.

• Thatch can prevent effective use of chemicals and fertiliser applications.

• Excessive thatch affects ball pace, ball bounce and ball roll.

• Thatch will also affect the traction and shear strength of the turf surface.

• Thatch will affect turf grass quality.

What is Thatch?

Thatch is a layer of living and dead organic matter (OM) that lies between the green vegetation and soil surface. It is composed primarily of turfgrass stem and root tissue materials. This living material is continually breaking down into layers of thatch material, which over time increases in depth. In some cases over 5mm of thatch can accumulate in any one growing season.

The rate at which this thatch layer builds up will be determined by many factors:-

• Type of grass species, some grasses are more vigorous and produce more vegetative matter.

• Soil conditions/soil bacteria present/soil pH.

• Weather conditions/climate.

• Maintenance of the sward.

Biologically some grass species produce more thatch material than others, particularly fescue and bent grasses that vegetatively produce a lot of stem and root tissue (rhizomes and stolons).

The condition and type of soil will also influence the amount of thatch produced. Loamy and clay loam soils are more fertile than sandy soils thus promoting active plant growth. The amount of beneficial soil organisms (fungi and bacterial) present in your soil will determine the level of thatch present. They play an important role in breaking down plant tissue. Any soil condition that reduces the numbers of these organisms, e.g., a pH that is too acid or alkaline; heavy, wet soils can slow the breakdown of thatch.

Climatic conditions will also influence the amount of thatch produced. Grass growing in a shaded environment will produce less thatch compared to a grass plant receiving optimum climatic conditions (plenty of light, air and water).

However, it is generally the choice and regularity of certain maintenance operations that determines and controls the amount of thatch you will have in your sports turf facility. Heavy nitrogen fertilisation and irrigation can contribute to thatch build up because they cause turf to grow vigorously and produce more organic matter.

Thatch control

Preventing thatch by proper establishment of the sward and effective cultural practices is easier than having to deal with all the problems that are caused by thatch and its removal.

When establishing turfgrass swards, select species or cultivars that are appropriate for the intended use (football, golf, cricket, bowls), environment and desired maintenance level (school, club, county).

If your existing turf produces large amounts of thatch, try to slow its production by altering present maintenance practices:-

• Apply appropriate balanced fertilisers at rates and timing appropriate for the type of grass being grown.

• Avoid excessive nitrogen application.

• Irrigate deeply and infrequently; avoid light, frequent watering.

• Monitor soil conditions, carry out soil analysi, testing for soil Ph, organic matter content and nutrient values.

• Implement variable aeration techniques combined with effective topdressing practices.

Adjusting the soil pH to between 6.0 and 7.0 may allow soil bacteria and fungi populations to increase. High populations of bacteria and fungi are essential for breaking down OM. Reducing the use of turf pesticides, especially fungicides and insecticides, can also increase microbe populations.

Applying top dressings coupled with good aeration work will help the breakdown of OM by providing an ideal environment for increased micro-organism activity which in turn increases the breakdown of plant tissues.

Mechanical removal of thatch

The method and type of machinery used will be dependant on:-

• Size of the area to be scarified.

• Surface - fine turf or outfield turf.

• Depth of operation.

• The amount of debris to be removed.

• Surface damage.

• Time allowed.

• Soil type.

• Grass type.

• Retention of organic matter.

• Location and aspect of site.

In general, the level and quality of scarification is dependant on the type of machinery available. Not all groundstaff have their own machines and, if they do, may have a particular type that can only achieve a certain level of working depth and performance. Hiring can be beset with problems. The machines may not be available when you want them, so it is important to check availability and book early when hiring. Hired machines can often be unreliable, often breaking down or having worn blades. The advantage of purchasing your own machine means you have exactly what you need to do the job you want.

The choice of machine is critical. It is no good spending money on a machine that does not or cannot remove the quantity of debris desired or achieve the depth of penetration required. It is best to seek advice and ask for demonstrations of different manufacturers' machines. This will enable you to find one that meets both your facility needs and budget.

Below are a few example of the types of scarification equipment available:

Verticutting units for de-thatching	Ride on mowers with verticutting units for de- thatching.

Fine turf scarifier, removes and controls thatch on all fine turf areas.	Heavy duty powered scarifier, de-thatcher and linear aerator.

All surface scarifier for vigorous renovation.	Combined de-thatcher and linear aerator with collection for larger areas.

Within the last couple of years we have seen the development of new turf renovation machinery, particularly the Koro Field Topmaker. For quick turf rejuvenation, the tractor-mounted Field Topmaker has blades that can be set from 4cm above ground to 6cm below, to skim off the top layer of vegetation. At a high setting, the Field Topmaker will fraise mow the ground to remove irregularities and restore a level surface ready for overseeding. Set lower, the standard blades remove thatch, organic material and shallow rooting grasses, leaving the roots of the desired species, like perennial ryegrass, intact for re-growth. The Field Topmaker can be fitted with deep vertical scarifying blades to carry out linear aeration up to 2". Simultaneously, the material is removed on to the hydraulically driven conveyors into a trailer alongside. By cutting through and removing much of the thatch, water, air and nutrient permeation is encouraged and, because vertical blades sever lateral growth, conditions for a healthier and more active sward are provided.

General

The commonly accepted time for thatch removal is in the autumn during the end of season renovations. However, with the development of groomers and verti cutting units on mowing machines scarification can be undertaken on a regular basis. In golf and bowls situations these units are often used on a weekly or fortnightly basis.

The other recognised time is in the spring, but generally involves a lighter scarification to minimise any damage to the playing surface ahead of the new playing season.

Be careful not to over do the scarification. Using a vigorous machine on a fine turf may have a detrimental affect.

Keeping thatch under control is a key maintenance requirement, and today's machinery is making this once arduous task significantly easier.