Autumn is almost like a second spring growing season for turf, so remedial work needs to begin in good time to make use of good weather and warm, moist soil. September and early October are ideal months for turf germination, root growth and recovery, but are followed by November as growth shuts down when temperatures drop below 6OC.
We need to begin remedial work early, first with aeration and topdressing, and then fertiliser and beneficial organism application. Robust turf growth, not soft and lank, has a better chance of resisting winter disease, wet and cold stress, and then responding quickly to meet your exacting needs in the following spring.
Aeration and thatch removal are first priorities, especially where dry summer conditions have limited aeration operations. Gas exchange into the organic layer and rootzone is essential for healthy turf growth and disease suppression. Roots need to respire, and oxygen encourages development of aerobic microbes that fight disease and decompose organic matter into valuable humic acids and soluble nutrients. Verticutting encourages upright growth and regrowth within the sward and permits shallow aeration.
Scarification removes thatch and allows air penetration into and through the lower organic layer. Spiking, slitting and hollow coring allow aeration to greater depths - down to 30cm - where root action is so important.
Deeper aeration, with specialist compressed air equipment, is possible and desirable where compaction and panning in lower soil strata restricts rooting and impedes drainage and gas exchange.
Topdressing, with a suitably open substrate after hollow core aeration, establishes air and water channels through the organic layer into the rootzone, maintaining aeration and water percolation for months.
Attend also to drainage, especially on heavier soils and sub-soils where "ponding" under greens can occur. Poor drainage gives rise to root death through lack of oxygen, and benefits many soil pathogens. Salt accumulation damages roots too, another good reason for good drainage.
After aeration procedures, water and nutrients need to be managed. Water infiltration and percolation through the turf continues to be important to transport nutrients and beneficial organic compounds through the soil or substrate to the roots to support recovery growth.
Hydration aids (surfactants), in combination with kelp seaweed extracts, encourage water to percolation vertically and horizontally through the substrate. Seaweed also supplies beneficial cytokinins and auxins for enhanced root development and turf regeneration. Avoid long lasting wetting aids late in the year. Amino acids and similar humic and fulvic organic acid products will also benefit rooting bulk, depth and nutrient availability and capture.
Organic compounds encourage a healthy biota in the soil or substrate to recycle nutrients, regulate pH and compete and suppress pathogens. Natural processes are encouraged to work for you; effective turf nutrition is far more than applying fertiliser.
Autumn fertilisers are essential in recovery and winter resistance. Soil analysis of principal areas is recommended to establish the turf's individual nutrient needs. Nitrogen is required, but in modest amounts. Phosphate is vital for energy transfer and root development. Potassium regulates water and sugar transport, so is vital in autumn for firm strong turf growth.
Autumn and winter fertiliser provides suitable seasonal nutrient balance, e.g. 5:2:15+2MgO+TE, even better if they contain organic materials such as amino acids and beneficial bacteria to produce ideal recovery and root strength.
Some more unusual fertilisers have strong benefits for turf in autumn. Potassium Phosphite (not phosphate) stimulates meristem activity, so enhancing both root and shoot development. Phosphite fertilisers are rapidly absorbed and transported through the turf to areas of need where they aid the turf's regeneration and disease resistance. Typically apply at around 50ml per 100m2 in 10 litres of water.
Potassium silicate (the forgotten element) fertilisers have a hardening effect on turf, producing erect growth and aiding air penetration, so can physically reduce disease incidence and enhance playing surface quality. Application rate is similar to the phosphite.
Iron fertilisers are in common use for hardening and darkening turf, so are useful later in autumn. Iron sulphate is also useful in lowering pH, but progressive applications may be needed.
Sulphur, as elemental sulphur used as mini-prills that are easy to spread, provides an essential major nutrient and also slowly helps in pH reduction, making the soil less attractive to worms and coarser grasses.
As temperatures fall through the autumn and dampness rises, fungal problems increase and grass growth slows, so resistance to disease and recovery from attack is slower. Good management practice will reduce the incidence and severity of disease attack, but the inevitable will happen.
Review your armoury of fungicides now and be prepared. To avoid resistance building in the pathogens, use a rotation of active ingredients with different modes of action to break this cycle. If 10% of a fungal population survives your attack and prospers to multiply, resistance will be far worse in the future and your problems even greater. Rotating your actives will almost eliminate this.
More and more bio-fungicides are entering the market. These are based on selected, effective strains of fungi and bacteria with three modes of deterrence to the pathogens.
Bacteria, such as Bacillus subtilis, colonise the roots and benefit from carbohydrate excretions from the roots. The bacteria produce exudates with anti-fungal properties, thereby preventing pathogens attacking the roots that are surrounded by a sheath of beneficial bacteria.
Fungi such as Trichoderma virens (Trichoderma harzianum) colonise the substrate, thereby physically inhibiting pathogen spread and digest the pathogens.
Some strains of Trichoderma also effect auxins (plant hormones) in roots, promoting more lateral growth.
Watch out for these and other bio-fungicides and bio-pesticides and predators for rootzone pests, thereby widening your range of control products and reducing your dependence on toxic chemicals.
Combine them with beneficial organics and good management to produce a quality playing surface, with less reliance on conventional nutrients and pesticides, and lower environmental impact.
Bill Riley BSc. Hons. Dip. Geoscience, Vitax Ltd.