The Danish Forest and Landscape Research Institute, DFLRI, researches in managing green areas without the use of pesticides, as this is a major issue in Denmark today. The very interesting results so far show that a proper management, including regularly overseeding, can provide a turf quality, in terms of weed control, close to the quality obtained by the use of herbicides. At the same time, proper management will help securing high quality sports fields that are safe to play on, and have an increased tolerance to diseases due to a more vital growth of the grass.

Below are extracts from an article written by M.Sc. Jørgen Fischer, Agricultural Senior Consultant at DFLRI, published in the magazine “Grønt Miljø” (Green Environment) No. 4, 1999.

Good Lawns and Football fields made of Grass Without the Use of Pesticides

It is difficult to fulfil user requirements regarding lawn quality in public areas, especially football fields, without using pesticides. However, when specific technical demands are known, and the necessary resources spent, it is possible to maintain a good lawn quality.

From a user point of view, lawn quality is determined by factors such as drainage, surface stability, density of the grass, evenness and wear tolerance. The amount of weeds in the lawn is of major significance in this context. The presence of many weeds in a lawn will reduce the lawn quality, and make the lawn more uneven, less dense and less wear tolerant. Until now it has been possible to control the amount of weeds in a lawn with herbicides. However, a weed control of the future without the use of herbicides will depend on the methods used and the level of maintenance.

To maintain a high lawn quality in the future, the growth parameters of the lawn must be optimised. This will require a change in the methods of care applied to intensively used lawns. Optimizing the growth conditions of the lawn is possible by means of a more intensive application of already known methods of care and a more carefully controlled use of the lawns.

Fertilizing

Without nutrients - no growth. And growth is a prerequisite for a high quality lawn. On account of environment and growth, fertilizing plans should be prepared on the basis of soil analyses, and quantities of fertilizers should be applied to the area several times. To extract the nutrient from the fertilizers, to obtain a more even growth and to reduce the risk of loss of nutrients by leaching, it is recommended to distribute fertilizers on 20 April, 20 May, 20 June, 10 August and 20 September under Danish conditions.

Precision fertilization is possible with simple equipment

Cutting

The height at which the grass is cut has a heavy impact on the growth of the grass. The normal height of the grass on lawns/football fields is usually 3.0 – 3.5 cm. The nature of games played on the lawns /football fields etc. often calls for a height of 1.8 – 2.8 cm. Nevertheless, this reduces the vitality and wear tolerance of the grass, as well as its resistance to pests and diseases. A very short cutting of the grass will thus always have a negative effect on its competitiveness towards weeds.

It is recommended that the height and frequency of the cutting is varied according to the growth of the lawn. Only one third of the leave length should be removed at each cutting. Decorative lawns, sports fields etc. are to be cut with a cylinder mower, which does not tear the grass but provides a clean and uniform cutting. In this way the risk of diseases is minimized.

Vertical Cutting

Old grass cuttings, shrivelled leaves, stems etc. can form a layer of undecayed plant material called “thatch” at the bottom of the sward. A lawn with a thick thatch layer will slowly degenerate because the water, fertilizers and air cannot penetrate properly into the soil beneath. Under moist conditions, a thick thatch layer can also make the surface of the grass spongy and increase the risk of succumbing to disease. Furthermore, the thatch layer reduces the wear tolerance of the surface, furthering the formation of bare spots allowing weed seeds to germinate quickly.

Since the thatch layer influences the growth of the grass negatively, lawns must be cut vertically. The felt layer is then cut by knives at intervals of 2-3 cm. Following this procedure, the runners and stems of the lawn are cut thus creating new, independent plants and more tillers.

Vertical cutting must be done when the lawn is in good growth, i.e. in the periods 1 May – 20 June, and 1 August – 20 September. However, never in dry periods. Fertilizers should be distributed right after the vertical cutting.

Illustration of the effect of vertical cutting

Small machine for vertical cutting. On large areas bigger machines are needed.

Re-Seeding

When using lawns/sport fields intensively, bare spots appear inevitably and require a re-seeding. With pesticide free lawn care, the need for re-seeding will be increased significantly, in order to avoid the establishment of weed seeds, which germinate quickly. Re-seeding should therefore take place as soon as worn patches appear on the lawn/field.

Re-seeding is carried out with special machines, which either cut down into the grass layer to place the grass seeds into grooves at a depth of 1 cm, or prick small holes and sow the seeds over the entire area. In the same process, some machines can also topdress to cover the seeds.

Seeding can be done with simple equipment if vertical cutting has been done prior to overseeding

In principle, re-seeding can be carried out throughout the entire growth period. However, the best seeding periods are 1 May – 20 June and 20 August – 20 September.

This type of machine places the seeds in small holes thus improving their establishment.

Top Dressing

Top dressing is a prerequisite for a high lawn quality. Top dressing keeps the lawn even, protects the lawn growth area and ensures a better germination on re-seeding. The addition of top dressing helps stimulating the growth and vitality of the grass. Top dressing materials are sand, siftes sandy loam, or a sand-compost mixture. When choosing the top dressing, the range of grain sizes is important. If sand is used, it is recommended to mix it with siftes loam or compost. However, the compost should make up no more than 25-30% of the mixture by volume.

Topdressing with sand

Dragging with a net to level topdressing

Subsequent to top dressing, levelling by means of a drag leveller is recommended, and is normally done in connection with vertical cutting and re-seeding.

This type of net for dragging is also for surface levelling

Aeration

The use as well as maintenance of the lawn/field will often lead to compaction of the top 5-6 cm of the soil. Such compaction reduces the growing conditions of the grass, due to the fact that the exchange of gases and permeability of water are reduced. Aeration can, to some extent, remedy the problem. 15-20 cm long, thin slicing knives cut down into the soil helps increasing a gaseous exchange and the percolation of rainwater. The need for aeration is most important in April, September and October, but lawns/sport fields having a clayey and fine-grained growth layer should be treated when needed.

There exists various types of aeration machines

Losening of the Soil

When not only the top few centimetres of the soil, but the top 30-35 cm have been compacted, it must be thoroughly loosened. This can be done with a vertical drainage machine.

Vertical drainage is most effective when done subsequent to a top dressing of the area. The soil is then losened with the vertical drainage machine, and with one or more subsequent levellings, most of the topdressing is distributed into the holes made by the drainage machine. The best time for vertical drainage are 1 May – 20 June and 20 August – 20 September.

Heavy machinery for losening of very compact soil

Loosening of soil in depth

Irrigation

Water is vital for the grass. Without water, the plants cannot absorb and transport nutrients, maintain their liquid balance or regulate their temperature. To provide the grass with optimal growth conditions, the plants should be irrigated with 30 mm per week according to the local evapotranspiration – and must always be based on rainfall – evapotranspiration measures. Under Danish conditions irrigation is required in the period May-August. Measurements of precipitation and evaporation, as well as known limit values for water deficiency enables the growth of the grass since the water consumption is tailored to suit the actual needs of the grass. If irrigation is commenced in a dry period, it is important to continue watering throughout the period. “Spot irrigation” should never be done since this will make the root network of the grass superficial and less drought-resistant.

Irrigation is easily done with the right equipment

Use

Grasses are living plants that, like all other living organisms, depend on the climate, and in periods without growth or with limited growth, the grass has no wear tolerance. Grass is therefore particularly susceptible in the Winter period that is from October to April, and in dry periods.

An intensive use of the lawn, in periods where the grass is not growing, will result in the formation of bare spots which will allow an easier establishment of weeds. If pesticides are not used, limited use of the lawn/field is therefore imperative in non-growing periods.

Possible, but more expensive

Lawn care without the use of pesticides is a realistic solution provided that a long-term care and maintenance plan is worked out. This planning must be prepared so that the grass will be given optimal growing conditions allowing it to be as competitive as possible.

In cases where sports fields are used a lot, and the wear therefore rather substantial, time must be allocated for the necessary maintenance and resting periods of the grass.

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Maintenance of Green Areas - Without the Use of Pesticides