How do I control moss in fine mown turf?
Mosses are primitive plants that are known collectively as bryophytes. These non-flowering plants are found in a wide range of habitats – including within fine mown turf swards – and consist of a slender, soft and fleshy stem, green or brown leaves and slender roots called rhizoids which absorb water and anchor the plant.
Types of moss
There are around 600 species of moss in the UK but, thankfully, only a few have a widespread impact on mown turf:
- Upright mosses (Polytrichum): favour dry, acidic soils and are therefore commonly found on mounds near to golf course bunkers.
- Trailing mosses (Hypnum, Eurhynchium): also known as fern-like mosses. These occur in areas suffering from poor drainage, excessive shade and thick thatch accumulation.
- Tufted mat mosses (Ceratodon purpureus and Bryum): often found on acidic soils that have been scalped as a result of being mown too low. These mosses will get significantly worse unless dealt with quickly and effectively.
Moss establishment and growth
Mosses are opportunist plants which will establish within a turf sward when the grass covering is too thin or growing too slowly, or when the grass has been mown too closely (scalping). Excessive growth is also exacerbated by persistently wet conditions (e.g. due to poor soil drainage) and in swards with excessive levels of thatch. Surface compaction, poor soil fertility, heavy shading and low soil pH also encourage mosses to out-compete grass plants.
Cultural control measures
The key cultural control measure for removing mosses from grass swards is scarification: this simple process will reduce the thatch content within the sward, thereby limiting the potential for mosses to ingress.
A scarifier fitted with light-duty fixed knives (or heavy-duty knives if the thatch layer is deep) will quickly and easily remove unwanted material, but it is important to remember that scarifying can also remove a lot of favourable plant material so it should only be carried out when the turf is actively growing and able to recover quickly.
The first scarification of the season should be carried out in the spring with any dead moss removed soon afterwards. Early autumn (September) is often the ideal time for deeper scarification work to be done: for a cleaner result, mow the turf a little shorter than normal before scarifying, but be careful not to scalp the sward.
Moss growth can also be kept under control by alleviating soil compaction: compacted soils lack enough pore space within the soil structure which causes slow grass growth, thinning of the turf and surface water retention, all of which can promote the ingress of mosses.
Aerating the soil using slit tines, solid tines or hollow tines will create more pore space within the soil profile, thereby enabling the existing grass plants to grow more vigorously and compete more effectively with mosses. Shallow compacted soils should be aerated to a depth of 75-100 mm, but deeper compactions may require a hollow tine working to a depth of 300 mm or more. Any aeration work should only be carried out when turf is growing and therefore able to recover quickly.
Non-cultural control
Because most moss killers are palliative, the majority of mosses will soon return after treatment. The first step to the long-term control of mosses is therefore to find the cause(s) and to remedy them.
An application of a good lawn sand – made up of sand, nitrogen (as ammonium sulphate) and iron sulphate – can help to desiccate moss plants: this type of top dressing should be applied at a rate of 34-75 g/m2 at a time when conditions are conducive to healthy grass growth. Once dead, the moss should be removed by carrying out a light scarification. The mowing height should subsequently be raised to allow grass plants to recover more vigorously, and an aeration should be carried out to prevent mosses returning.
Sward nutrition as a moss inhibitor
An appropriately timed application of an iron-based fertiliser will also help to control and inhibit mosses: Germinal’s G14 Alleviate Fe 4-0-10 (+8% Fe) is the perfect high iron fertiliser for protecting high-value turf areas (sports fields, golf greens, golf tees and bowling greens, etc.) throughout the growing season, but especially through the autumn and spring when mosses are at their most prevalent.
In addition to its high iron content which hardens grass plants and protects them from disease, G14 Alleviate Fe also contains magnesium – a vital component of chlorophyll. The subsequent increase in chlorophyll that G14 delivers ensures good grass plants metabolism resulting in improved plant growth.