One of the most diverse plants on the planet, moss is the bane of many groundsmen and greenkeepers. It will happily grow anywhere; on greens, tees, synthetic and hard surfaces, patios and pathways. So, what's the best way to get rid of it and can you do anything to prevent it in the first place?
Moss, like every living organism, requires moisture. The difference between mosses and other plants is that they do not require a root system for survival, though some produce a structure called rhizoides.
Whilst many take nutrients from the substrate directly beneath them, a lot of mosses can also survive in areas where moisture and nutrients pass over the leaf. They are also organisms that, in comparison to grass species, can tolerate shade and poor drainage.
These are special qualities that help us understand why they can be found on most surfaces, even hard surfaces such as roofs and pathways.
The high levels of moisture, mild temperatures and a competitive growth habit over the winter period have therefore been a major contributing factor to the amount of moss we witnessed in the early spring.
Mosses are plants that do not have a vascular system. They are part of the order called Bryophytes. As well as mosses, Bryophytes also contain the groups Hornworts and Liverworts.
After flowering plants and ferns, mosses are the most diverse form of plants, with over 10,000 species in more than 700 genera; nearly twice as many as all the mammals on Earth.
In addition to not having a vascular system, they also have no woody parts. The lack of a vascular system makes them susceptible to desiccation and, therefore, they tend to be found in damp, moist and even aquatic habitats, although not exclusively, and some species have remarkable adaptations to very dry habitats.
Moss can be a problem within turf, whilst the appearance of hard surfaces, such as tennis courts or patios, can be compromised by mosses. These two areas need to be considered separately, as they require different solutions.
Mosses require a different solution to liverworts, therefore it is useful to see what characteristics differentiate the two groups.
Acrocarpous mosses are usually unbranched, or almost so, and have an erect habit, like small trees.
An example of a common acrocarp is Silver thread moss (Bryum argenteum). This is commonly found on acidic soils, grasslands, woodland rides, soil banks and waste ground, and is notable for its large (3.5-5mm long), cylindrical, drooping capsules, which ripen in spring and summer, and are borne on a reddish seta (stem that supports the capsule) up to 3cm tall. Acrocarps are never regularly pinnately (fern-like) branched, but have a central stem and leaves coming off that stem.
Almost all pleurocarpous mosses are freely branched, often either pinnate or chaotic. They frequently form dense intricate mats of elaborately branched stems. A common garden moss is Rhytidiodelphus squarrosus, so named because of the squarose nature of the leaves which bend back upon themselves.
Liverworts are split into two groups, leafy and thallose. Like mosses, leafy liverworts have stems and leaves, but the leaves are arranged differently on the stem, often with two leaves placed laterally and a row of smaller 'underleaves' below. Thallose Liverworts don't have recognisable leaves and stems, but consist of a prostrate, flattened, strap-like or branching structure called a thallus.
Mosses can be separated into three sub-classes. These three sub-classes comprise the following:
Sphagnidae: more widely recognised as sphagnum
mosses. There are over 100 species found worldwide
Andreaeidae: generally found in alpine situations
Bryidae: comprises over 10,000 mosses, and therefore is fairly common within the UK
As the Bryidae sub-class is so broad, it is normally broken down into the acrocarpous or pleurocarpous sub-groups. The easiest way of distinguishing between these two is that acrocarps are normally tufted mosses, whereas pleurocarps are sprawling. The defining features of acrocarpous mosses are that they are unbranched with an erect growth habit. Pleurocarps form mats of growth through freely branched, often fern-like, branches.
How do we control moss growth in a turf environment?
The traditional method of moss control typically utilised the use of lawn sand and other cultural practices. Whilst there are many instances where these processes could still be advised, there has been a slight improvement in the technical ability to beat the problem at the present time, at least for pleurocarpous mosses.
In a professional setting, many advisers would recommend treating the area with soluble iron sulphate, which would cause the moss to die off, allowing easier physical removal of the organism. This would have the added benefit of 'greening up' the sward without causing excess growth.
The growth habit of an acrocarpous moss is a contributing factor to why they are more difficult to control in general than their pleurocarpous counterparts. Essentially, with a tufted, more vertical growth habit, scarification/verticutting often does not have the desired effect.
Many golf and bowls greenkeepers will be familiar with the invasion of a moss known as silver thread moss (Bryum argenteum). This sub-species is of particular nuisance due to its rapid colonisation of weak areas and an ability to withstand some chemical control.
As moss is an advantageous species, the important thing is to try and ensure a competitive growth habit by the individual grass plants. Ground coverage, especially heading into the winter, is therefore essential.
What else can be done to reduce the risk of moss invasion/establishment?
Ensure adequate irrigation without over-watering. Many sports complexes around the country utilise an automatic irrigation system. In periods of stress, it would be advisable to water thoroughly, but to requirement. Over-watering can lead to other unwanted problems.
Find a balance in mowing height. Particularly in golf and bowls, mowing height plays a significant part in how the ball reacts with the surface. Ensuring you can find a balanced mowing height to allow good coverage without affecting playing quality is important in all sports in terms of moss reduction.
Reduce thatch. The utilisation of controlled frequency verticutting and deep scarification during periods of good recovery will reduce the organic content within the thatch layer. Reducing this moisture holding ability within the organic horizon of the soil is very important in moss control.
Aeration, aeration, aeration. As with anything in a sports surface, ensuring the best aeration will help provide a competitive grass sward. As mosses prefer compacted, moist soils, reducing the compaction and increasing drainage ability is a great tool in reducing the efficacy of moss invasion.
Removal of surrounding causes of shade. In areas that are prone to moss, look around the area and whether anything can be done to reduce the shade/increase direct light levels (e.g. removal of tree limbs etc). As mentioned previously, moss is highly competitive in shade over grass.
Overseeding. Overseeding in the autumn is recommended due to a more reliable amount of moisture and mild temperatures promoting early germination and establishment. Ensuring good establishment could be key in increasing coverage as you head into winter, particularly in known bare areas.
A balanced fertiliser programme. Obviously, with all of these control methods, it is important to strike a balance between the needs of your customers/visitors and the effective control of moss. Following this sort of integrated approach in general should provide an excellent basis for the production of quality surfaces. Therefore, the effective control of moss could/should occur as a by-product of solid greenkeeping techniques.
Timing and tips on moss control.
This situation can be alleviated with aeration, generally undertaken in the spring or autumn when sufficient warmth and moisture are available to enable the grass to repair. A typical renovation will involve applying a moss control product, a herbicide that will also control certain broad-leaved weeds, or a sulphate of iron based product often as a soluble powder, within a fertiliser or as a liquid. Ensure that the moss is damp, not wet through, but able to absorb the fluid being applied.
For moss control, ensure water volumes are high to ensure good coverage and enable the fluid to move over the leaf surface by capillary action. It is advisable to rinse out the sprayer thoroughly as soon as spraying is complete, as the iron will degrade any metal surfaces it comes into contact with. Iron does not mix well with many products, and it is advisable to 'jug mix' any products before attempting to apply them.
Once the moss has died - yellow/brown with herbicide or black and breaking up if treated with iron - it should be thoroughly scarified out of the surface. In areas that have been neglected for a while, moss can be the dominant species and, in these situations, the amount of moss that is pulled out of turf can be staggering.
It is then important to stimulate the grass with fertiliser so that it can respond and fill in the area that was occupied by moss. It may be necessary to overseed into the sward to provide vigour and assist in the recovery of the sward. Topdressing may also be required to make certain that the seed is in good contact with soil.
Soluble iron is the most economic way of blackening the moss in order to then scarify out, but this should only be undertaken if sufficiently vigorous conditions exist for the grass to compete against the moss potentially re-infesting.
Many people use the widely tried and tested method of applying lawn sand with the aim of burning the moss out and then scarifying/brushing out the dead moss debris.
Lawn sand is a mix of one part sulphate of iron, three parts sulphate of ammonia and twenty parts dry sand. It is applied at the rate of 140g per square metre. The sand material acts as a carrier for the active ingredients (iron and ammonia). It is important when using these materials to ensure that they are spread evenly over the turf surface. The best method of spreading lawn sand is by using a spreader.
It is important to calibrate the spreader in advance to see what spreading rate it gives when operated. Simply fill the spreader with some dry sand and operate it over a measured hard standing (tarmac, concrete, paved) area. This enables the sand to be swept up so it can be weighed afterwards.
Once you have the weight of the material spread over a given area, you can calculate how much has been spread over a square metre. Using this information, you can work out how much material your spreader is spreading. Most spreaders have a sliding aperture which can be adjusted to give a set desired application rate. Once the amount spread has been calculated over the given area, adjust the aperture accordingly.
You should also note the spreading width of the spreader when operated at a walking pace. If the spread is five feet (two and a half feet either side, then that will be your working width. Do not overlap when turning. You could lay down string lines at five feet intervals to ensure you do not overlap, but most people tend to use their mowing bands as a guide.
Windy conditions can also affect the spreading rate. Ideally, you need to apply lawn sand on a dry day with little or no wind.
Overdosing or applying lawn sand in the wrong conditions (when soil is too dry) will cause the sward to burn/scorch. It is vitally important to ensure you apply as per manufacturer's recommendations and during the right weather conditions.
It should be safe to walk on the turf after it has been watered or received sufficient rainfall to wash the material into the soil. It is important to water the turf within the first forty-eight hours of any applications if there hasn't been sufficient rain.
Lawn sand works because the powdered active ingredients (iron and ammonia) clings to the moss and broad leaves of the weeds, thereby burning and severely scorching their plant leaf tissues.
The treated areas will begin to show results quite quickly. However, the speed of die-back will be dependent on weather conditions and how active the moss is. The moss will begin to die back usually between one and four days after application.
Additionally, lawn sand also provides a tonic for your sward and has a definite 'greening' effect. It is normally applied in late spring but, where moss is a problem, it can also be re-applied during the summer.
Another alternative is to give the grass a little encouragement, with a low analysis fertiliser that also contains the sulphate of iron required for moss control.
Once the grass is growing vigorously, it should continue to out-compete the moss, providing a regular maintenance programme is followed.
Methods of control on hard surfaces such as tarmac
Regular brushing with a stiff brush can help reduce the build-up of moss on a surface. However, once it has established, the easiest way of removing the moss is to use a herbicide. Application rates and preparation should be strictly adhered to in order to obtain effective results.
Once the herbicide has been applied, the moss dies and will degrade, requiring no further input. These herbicides should not be used on moss growing within turf.
Methods of control on artificial playing surfaces
Small amounts of moss and algae are not necessarily indicative of poor maintenance. However, large areas covered in moss and algae are and present a potential slip hazard to the player. In certain cases, the presence of moss and algae can be so bad that it covers up and hides the line markings and the playing surface itself.
Moss and algae should not be allowed to establish on the playing surface, as they can create dangerous slippery conditions.
Try to prevent the conditions that favour the establishment of moss and algae, i.e. moist conditions, by maintaining good surface water infiltration and drainage.
Inspect the surface for moss or algae on a regular basis.
Treat any outbreaks of moss or algae with an appropriate propriety moss killer or algaecide, applying the moss killer or algaecide in accordance with the manufacturer's instructions.
Typically, routine moss control will require two treatments per year that coincide with growth periods in spring and autumn, with spot treatments carried out as and when required during the rest of the year.
Water based pitches may require several treatments per year, with the addition of regular deep cleaning, owing to the ideal conditions for moss and algal growth that water based surfaces provide.
There are also a number of algaecide products that can be added to the water tanks so that, every time you apply water to the playing surface, a low dose of algaecide is applied.