The big negative of the drought affecting the UK this year is very clear for anyone to see. The thinning and sparse surfaces on many golf and bowling greens has led to a long struggle for greenkeepers to maintain sufficient moisture to maintain plant health. One positive that you can take from this is that there is now the potential to introduce some different species into your fine turf surfaces to replace some very stressed out Poa annua once we get some rain and soil moisture back. Some people may feel that Poa annua is a perfectly acceptable species for golf greens, but in terms of overall year-round performance and ‘sustainability’ a bent and/or fescue sward usually wins hands down – but why?
· Poa annua requires high inputs of fertiliser and water to survive as it has a shallow root system.
· It is prone to many common diseases – particularly microdochium and anthracnose – two of the most common turf diseases in the UK.
· It tends to produce seed heads at any height of cut which disrupts surface smoothness.
· It produces soft, wet thatch that makes greens soft and holds moisture and fungal pathogens.
With the ongoing reduction in turf fungicides it makes sense to reduce Poa annua populations and increase bent and fescue content that do not suffer from the above problems.
Changing to a bent/fescue dominated sward is not an easy ‘quick fix’ and will take time. The benefits, however, are ultimately a better performing surface and less reliance on chemical inputs.
Get the greens ready for seed
The first stage of establishing bents and fescue in your greens is to make sure that you get thatch under control before heading into an overseeding programme. Putting down bent or fescue seed into an inch of thatch is a waste of time and money. Overseeding a hectare of greens is not cheap and it’s important to maximise every seed in the bag – you may get germination in a thatchy green, but long-term survival is unlikely.
If you have a dense thatch layer, save your money on grass seed and focus on thatch removal first otherwise you’ll always be fighting a battle you’ll never win. Do not get too hung up on the percentage of organic matter in your surfaces if you have it measured – it is a good indication of potential thatch, but it’s useless unless you have a good look at your soil profile.
Make sure you look at your soil profile
The type of organic matter you have in your soil is as important as the percentage. 3% organic matter in the top 20mm can give you a problem if it’s a dense thatch layer, but 10% organic matter in the top 20mm could also be a rich, humic soil with excellent infiltration rates, good drainage and a firm surface. Getting hold of a good soil profile sampler and checking your soil profile regularly can be really informative as to where you are with your soil.
Get the soil working for you
A good scarify or hollow core will remove thatch from above. A microbially active soil will break thatch down from below. Attack thatch from both above with mechanical methods and from below with biological methods. Create a healthy, diverse microbial-rich soil that will feed on the thatch layer and break down quicker than you build it. The use of high quality composted organic granular fertilisers such as Sustane combined with a good biostimulant that feeds the soil such as Essential Plus in a sensible year-round programme can bring huge benefits to turf quality and the ability to reduce thatch issues and promote bents and fescues.
Can you accelerate thatch degradation?
One little add-on to your programme could be the DeThatcher product from Growth Products. This contains a blend of thatch digesting microbes and enzymes that break down the tough to digest materials in a thatch layer. Protease, cellulase and amylase are enzymes that increase the rate of thatch breakdown and 3 separate species of Bacillus bacteria digest this material and produce even more enzymes to accelerate thatch decomposition. This is not a ‘wonder product’ that can be used in isolation with success – rather it will complement a sensible cultural programme and help increase the rate of thatch breakdown.
Sowing the seeds of success
Placing the seed at the correct depth is important. Ideally fescue must be sub-surface (4-10mm below) and bent needs to be as shallow as possible, but with soil-contact and protection from drying out quickly. ‘Pot seeding’ of fescue on many links courses is becoming more common – this involves cutting a solid tine flat across the bottom and tining to a depth of only about 10-15mm and then dropping seed down into these ‘pots’ to protect them. Dimple seeders and drills both work well if set up correctly – just make sure seed is at it’s optimum depth below the thatch/surface.
Soil temperature is important for good germination. Bent needs a warmer soil than fescue to pop and better success is often found towards the back end –August, September, October – than early season. Bent is good at surviving in the soil until warmth is there however, so all is not lost with cooler season bent overseeding. Fescue is not quite as well adapted to long term seed survival and requires soil temps of 8oC and above before attempting. Some will survive in a dormant condition in soil, but a larger percentage than bent will die. You can go earlier and later in the year with fescue and still get good germination.
Getting bent & fescue out of the ground is one thing – maintaining it as a permanent part of the sward is another. One big problem is mowing once the plant develops to the 2nd/3rd leaf stage – unless it gets a bit of time to develop it can get stressed back and die. One way of helping new plants is to make sure a sensible dose of Plant Growth Regulator is applied just before overseeding. This will slow down indigenous Poa growth and give the new seed a chance to compete. Regular light top dressings after the seed has popped will give the seed a chance to grow, but effectively cover the crown of the plant and reduce the damage to lower parts of the plant. Juts two or three light dressings can really help long term survival of seedlings.
What fertilisers are you applying at seeding time? Often when seeding, it is after some invasive renovation work such as scarifying or hollow coring and the temptation is to apply a ‘recovery’ fertiliser with a high percentage of instantly available ammoniacal nitrogen to push on growth and get the greens back their best as soon as possible. One problem with this will be you are pushing on growth from the existing Poa population and giving it a competitive advantage over any seedling emerging which have a limited root mass and cannot compete with mature Poa plants growing at an accelerated rate. Secondly, you are probably increasing thatch accumulation!
Getting this message across to golf club management is important if we are to have more success with our overseeding. Sacrificing an extra week or two of recovery time for a significant long term gain would seem a sensible strategy, but if management and members are not on board, the greenstaff will be the ones under pressure.
Use Mycorrhizae instead of fertilisers
An alternative to fertiliser at overseeding would be a mycorrhizal inoculant. Mycorrhizae are beneficial fungi that form a symbiotic relationship with perennial plants and allow to access nutrients and water more efficiently, reducing stress and improving health and growth. Mycorrhizae will not associate with Poa annua, so you are promoting perennial species only when applying our liquid endo-mycorrhizae and the benefits are for the life of the plant, not just for a few weeks after seeding. A single spray directly on to the seeds after sowing will help the plants resist stress and it will have lower water and nutrient requirements.
A little planning goes a long way with overseeding. Communicate with the management and get golfers to understand what you are trying to do – this can reduce post-renovation pressure to get greens straight back to perfection. Get conditions right before overseeding and plan maintenance for after the seed is in the ground. Even with all these things lined up and a bit of luck with weather it will still take years to convert Poa annua greens to perennial-species greens, but it’s fight worth fighting.
Geoff Fenn BSc (Hons)
UK Technical Manager