Bowling Green FAQ 1: Colour and thinning sward

Two common questions can be addressed here, effectively as one question: (a) The turf is turning yellow, has thinned and died off in places and is leaving unsightly patches. (b) We have a patchy coloured green with some areas growing, whilst other areas do not seem to be growing at all. It is now the end of June, so what might the problem be?

This could be due to many possible, often inter-related, causes, however, the more common ones at this time of year will be as follows:

a) A green that has a high percentage of annual meadow grass will typically also have a medium to high depth of thatch along with a relatively shallow root depth. Warm, prolonged dry weather, even with supplementary irrigation, will see the sward stressing and the annual meadow grass will be suffering and dying off in places. This species isn’t well adapted to the drying conditions, unlike the more desirable red fescue and browntop bent grasses, which would otherwise survive well during such conditions. Reflect on how solid tine aeration, a good soaking to depth and the raising of the height of cut can be implemented in the short term to ease the stress on the sward.

b) These conditions can typically occur on greens with shallow rooting, which is primarily due to too short a mowing, often removing an excessive amount of leaf on a regular basis, i.e. more than 33%-40% per cut, an undesirable depth of thatch, as well as the surface being relatively uneven with minor depressions. At the sward level, a minor depression of even 2mm-5mm can be quite significant, with some grass within a small depression being several millimetres longer than the adjacent sward, especially if the cylinder mower spans the minor depression. This greater grass length will show up as a greener colour than the shorter grass which is not in the depression, and the shorter grass will be showing signs of heat and moisture stress causing thinning, dying off and providing a contrast in colour with the healthier grass in the depression. In the short term consider raising the height of cut slightly and apply a light top-dressing. The green could be taken out of use on a Monday after a busy weekend, sarel spiked and then lightly top-dressed (~1 kg/m²), focusing applications on the greener areas which would be indicating depressions, and the material luted in carefully, with this being carried out within a day ready for play again on Tuesday.

c) The disorder dry patch might be a condition which is present, although don’t confuse this with dry conditions. If dry patch is present then solid tine aeration, along with sarel spiking, followed by application of a wetting agent and a thorough soaking in should help to improve growing conditions, especially the ability of the soil to retain water making it more available for plant growth. Once the turf has died off it will take time for the area to be re-colonised and recover and some overseeding and renovation work might be needed to assist the recovery.

If wetting agents have been used as a matter of routine and the conditions have occurred, then it is possible that they have been overused and their effectiveness has weakened significantly. Improving soil microbiology can help to restore a possible lack of micro-organisms which create good growing conditions and break down water repellent substances and organic matter as part of a more natural cycle. Reducing the application of fungicides will also help to restore an imbalance to the soil ecology.

d) Anthracnose might be a cause, so have a close look at the affected areas to see if the grasses can be easily pulled out and if there are any small black speckles at the base of the stems. A compacted, moisture retentive thatch sward with high annual meadow grass content, which is mown short and with inadequate nutrition, along with temperatures being routinely above 22C will provide an ideal environment in which anthracnose can attack and thin out the sward.

d) The sward might have been subject to leaching, especially if rainfall or irrigation has been excessive since a typical fertiliser application in April and is now suffering from a lack of nitrogen. A foliar feed supplemented with a mid-summer micro-granular feed would help restore any lacking nutrients.