The Groundsman

October 2013

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TECHNICAL UPDATE 27 The images above show two different depths of thatch on bowling greens. So what is thatch and where does it come from? • It is a build-up of partiallydecomposed plant material, which lies on the surface of the root-zone material, formed from: - Damaged plant cells caused by poorly set machinery (mowers) - Sheath growth particularly from Poa annua (common grass weed). • Slow break-down of the plant material, because of low-population levels of healthy microbes in the root-zone, which break-down the plant material. • Grasses such as those of the Festuca spp (Fescues), contain cellular lignin which breaks down slower than the lignin from other species. • Grass clippings? This has been shown to be a myth, if all mower clippings were not removed by boxing off, the increase in thatch build up would only be approximately 20 per cent extra thatch, (Adams et al 2000). The images above show two different depths of thatch on bowling greens. Poa annua (Annual Meadow Grass) This is the main weed grass of the UK, so its ingress into playing surfaces is a fact of life. This grass has a major impact upon the playing quality of bowling greens (Peel 1982), as it produces large amounts of waste plant material, which develop into thatch. Swards with a high percentage of Poa annua are slower by up to 18 per cent, as shown in the chart (below), (Conaway et al 1992). Distance non-biased wood rolls - grass species Poa annua Agrostis tenuis Agrostis castelina Festuc rubra commutata Festuca rubra literalis 5.00 5.50 6.00 6.50 7.00 Distance (m) 7.50 8.00 8.50 Management of the thatch layer. There is no one single answer to reducing the rate of thatch development. To achieve a sustainable green, in the long-term, relies upon adopting a holistic approach rather than focusing on a single issue. To achieve effective management of thatch, the programme will need to break the circle, (shown above), which ultimately results in declining quality of the playing surface. Therefore, the issues that should be considered when formulating the management programme for the bowling green include: • Maintaining a healthy root-zone • Suitable pH value and a balanced supply of plant nutrients in the root-zone. Although it is tempting to lower the pH value of the root-zone, this places the microbes required to break down plant material under stress, as they have difficulty multiplying. This results in low populations of microbes and a reduced rate of plant material break down - leading to increased thatch layer development. The amount of available nutrients in the root-zone will be depleted by the removal of clippings, rather than leaving them on the surface of the green to break down, thus releasing the nutrients they contain back into the root-zone. However, excessive and or unbalanced application of fertilisers to redress this depletion can results in lush or weak plant growth; resulting in plant material being discarded, contributing to thatch layer development. Sufficient rather than excessive irrigation Application of irrigation can, if not carefully planned, exceed the demands of the plant and the root-zone materials' ability to drain away excess. As a result, the air in the root-zone can become, if only temporarily, expelled by the surplus water, which discourages the development of a healthy root-zone microbial community. Also the temptation to frequently apply small amounts of irrigation can encourage shallow- rather than deeprooting plants; this type of irrigation programme also provides ideal growing conditions for Poa annua. t the Groundsman October 2013 Visit www.iog.org for more information and digital editions

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