SOME COMMON WEEDS OF LAWNS

DAISY: Bellis perennis (family Compositae)

General points

One of the commonest and most easily recognised weeds in lawns. Its prostrate habit is relatively unaffected by mowing and the spoon-shaped leaves smother, or can smother finer grasses to the extent of taking over large areas in a neglected lawn. The fibrous root system makes it a tough persistent weed. It has white flowers with yellow centres, flowers being borne on very short stems in many cases.

Soil type

Daisies are found in a very wide range of soils and appear to flourish equally well on light and heavy soils, irrespective of whether conditions are acid or alkaline.

Control measures

Lawn sand gives a fairly effective control as the flat habit of the leaves makes them susceptible to the scorching effect. Mowing has little effect on this weed. With selective weedkillers, it is usually best to make two applications as one may check growth but not give a full control. 24D or Mecoprop can be used. The best control may be obtained with a mixture of both, e.g. Supertox 30.

YARROW: Achillea millefolium (Compositae) General points

Fern-like foliage, dark green, persistent weed in lawns, erect flowering shoots if ..allowed to develop, with white or pink flowers. Can take over large areas in a neglected lawn. Its creeping underground stems can cause quick spread. Perennial.

Soil type

This plant thrives on light sandy soils but is found on most soil types. It is often noticeable in dry sandy soils. It grows well in closely mown turf.

Control

Yarrow is very resistant to M.C.P.A., 24D and Mecoprop. Lawn sand gives some control. Mecoprop and 24D (Supertox 30) gives reasonable control.

KNAPWEED: Centaurea nigra (Compositae)

General points

This is a tough plant with long narrow leaves and hard ribbed stems. Flowers, if allowed to develop, are purple. Perennial

Soil type

This is a weed which tends to be found most in soils with a high pH. It does well in heavy soils and is often found in damp positions, or conditions of poor drainage.

Control

It is moderately susceptible to M.C.P.A. and 24D and two applications of either weedkiller are more effective than one.

PARSLEY PIERT: A phanes arvensis (Rosaceae)

General points

This is not an easy weed to control. It is close growing, short stalked with fan shaped leaves (leaves are three lobed). Flowers are small and green. Perennial.

Soil type

Thrives on dry soils and in acid soil conditions.

Control

Very resistant to M.C.P.A. and 24D, even at maximum application rates. Iotox gives a good control. (This is based on Ioxynil and Mecoprop.)

MOSS ON LAWNS

Moss becomes established in a lawn when conditions are unsatisfactory for good growth of grass. It must be borne in mind that there are several species of moss, not all requiring the same conditions. It is often stated that shade, damp conditions, poor soil and very acid soil can all contribute to the spread of moss. These factors could also be the cause of poor growth of grass, but of major importance is the fact that moss can thrive in .adverse conditions and when it is well established, seriously inhibits the growth of grass.

Mowing can be an important factor in maintaining a good lawn and is the one most often abused. Mowing lawns composed of fine species two or three times a week and at a minimum of once a week at a height of 12 mm (0.5 inch) is the ideal.

Frequent mowing at this height will help to keep the turf vigorous. Very close mowing should be avoided.

Cultural methods of control

Moss does less well on soils which have a very open texture -hence top dressings of a gritty sand rather than a loam may help to keep the soil surface less congenial to a good moss carpet.

The type of grass makes a considerable difference. Agrostis tenuis – the bent preferred, but also Agrostis stolonifera, both resist moss much better than the fine-leaved Festuca rubra types. Poa annua lets in light and is a poor competitor in the winter which helps the moss keep a presence. Perennial rye grass – cut too short is a recipe for moss invasion.

Scarification helps to clear out the old ‘thatch’ on which moss grows well.

A grass sward denied nitrogen is a poor competitor so it is desirable to keep the grass in good growth. For this nitrogen is desirable, but so also are the essential cultural care items of excellent drainage and adequate irrigation in dry periods – good soil aeration by spiking and suitable top dressings, as well as a top soil into which the grass can enjoy a root run of 150 – 300 mm deep.

Mowing regularly is as important as keeping the bottom blade at a height which suits the species and the turf function. Very close cutting is not recommended and below 10 mm is extra demanding of the grass plants. Daily care of the groundsman to switch or mat off the dew is just one of the desirable steps which help to reduce the risk of moss invasion as well as fungal disease.

In short, the only permanent means of moss control is cultural. The aim should be to encourage the grasses to grow so well that there is no room for moss. As higher plants, grasses should be capable of this even under mowing, unless the lawn mismanaged.

Chemical methods of control

Ordinary lawn sand is a cheap, quick and fairly effective method which acts by scorching the moss and encouraging the growth of grass by the nitrogen content. Lawn sand can be made by mixing together 20 parts of dry lime-free sand with 3 parts sulphate of ammonia and 1 part calcined sulphate of iron. The mixture is applied evenly at 136 gms per square

metre (4 02 per square yard).

In extreme cases, where patches of lawn are bare of grass after treatments, it may be necessary to oversow the lawn in the autumn with a mixture of sterilised loam and sand and a fine grass seeds mixture, following vigorous scarification with a wire rake. Sufficient grass may be present to re-colonize the site, but over-sowing is usually needed.

In dry periods, sulphate of iron by itself at 17 mm per square metre (0.5 oz per square yard) may give excellent moss control and good weed control even for the difficult speedwell species like Veronica filiformis.

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