Beyond IPM (Part 2 of 3)

Much of the below is plain common sense and is practiced by many greenkeepers and groundsmen anyway, although it doesn’t hurt to reiterate some good practices with an aim to minimise and eliminate the use of pesticides.

Disease management
The implementation of an integrated disease management strategy that really emphasises the importance of having a good understanding of disease ecology along with correct cultural and physical practices, which are based on sound agronomic principles, can provide a solid foundation in controlling diseases, as well as reducing the severity of any actual damage caused.

However, the need to have plant protection products as a backup on which to call where severe disease problems arise is considered an important part of the current IPM regime, and we can’t pretend otherwise. [1] [2]

Having an appropriate and acceptable threshold below which no fungicides are applied is a key area that stakeholders should be more actively engaged with. Objective cost and surface quality implications for different levels of threshold can be clearly explained; something which is rarely undertaken at the moment.

What we need to do is really push the boundaries of effective cultural and physical maintenance practices to reduce the need for any form of fungicidal control. In practice this will be challenging, but having this as the focus of ‘Beyond IPM’ can help to reduce the reliant currently given to synthetic fungicides.

Disease Success Triangle

Disease Success Triangle

Three conditions are needed for a disease to be successful [3]:

  1. a susceptible grass, or plant;
  2. an active pathogen;
  3. a favourable environment (in particular conditions such as a stressed and shortly mown grass plant, water availability, relative humidity, temperature, soil texture, soil pH, soil organic matter and nutrient availability) . [4]

Cultural practices can be implemented to assist in alleviating the conditions for a successful disease attack. [5]

Particular activities can include:

o Improved grass and seed use:
Select grass species and cultivars that are more resistant to diseases and have this as a higher priority than some other criteria, such as seed cost or fineness of leaf.

Consider whether the blend of cultivars and mixture of species is better for an enduring surface rather than seeds and grasses that produce an excellent surface for a limited period of the year.

o Fertiliser applications:
Select fertilisers that complement the growth and development of the grass species being encouraged. Apply fertiliser at the correct time of year and in sympathy with the prevailing conditions; do not apply a fertiliser on a date that just happens to be the same as the year before.

Do not apply fertiliser at a rate that forces excessive growth otherwise the grass sward will be more prone to disease and less resistant to wear and tear.

Do not apply unnecessary amounts of nutrient, or nutrients that are not actually required. Carry out a soil test to at least provide the initial base information on which to build up your fertiliser programme: Don’t just rely on that but also the actual physical condition of the sward.

Consider whether the solution to one problem may contribute to the development of another problem.

A good example is that of applying a relatively high content nitrogen fertiliser to a grass sward during early August to solve the problem of Red Thread (Laetisaria fuciformis). This may, however, then encourage the development of Microdochium (Fusarium) Patch disease (Microdochium nivale), which is a much more severe and damaging disease of turfgrasses.

Consider the effect the fertiliser can have on the soil pH; will it produce an acidic reaction, or will it raise the pH to a more alkaline condition. Be careful if it raises the soil pH as this can then encourage Take-All Patch disease (Gaeumannomyces graminis). Have you been applying a controlled release fertiliser for a period of time an does this have a relatively neutral soil reaction? If so, then this will most likely be encouraging annual meadow grass, which as we know is highly susceptible to a range of turfgrass diseases.

Besides the obvious aim of wanting to encourage a strong, healthy and durable turf, the application of fertiliser can have a significant influence on the conditions that encourages disease activity.

o Moisture:
Turfgrass diseases have a particular need for soil moisture to enable them to develop. Surface moisture, especially in the form of dew, provides an ideal environment in which a disease can rapidly colonise a turfgrass sward in a short period of time. The application of a contact fungicide is often the first action taken to halt the spread of the disease when optimum conditions arise. The ideal action, however, would have been to implement improved cultural and physical practices that reduce the establishment of these optimum moist conditions in the first place.

Reducing dew is a key, but simple, practice that should be carried out as early as possible in the morning to remove this problem situation from being utilised effectively by fungal diseases.

Depending upon the species present the incidence of dew will be more significant for some species than others, so emphasising desirable species within a sward is essential.

Irrigation management can also play a major part in managing the risk of disease attack. In particular the quantity and timing of applications need to be effective and consistent in producing a microenvironment in the turf surface and rootzone that reduces the potential for disease development.

Do not over apply water, but also do not apply it on a little and often basis as this will encourage a moist surface layer, shallow rooting and weaker turf: all of which will make ideal conditions for a disease strike. If weather conditions are extremely hot and dry, especially during drought conditions, then the act of syringing a surface to keep it cool is not particularly going to increase the incidence of disease if carried out correctly.

o Aeration:
A well-aerated healthy rootzone encourages a turfgrass environment that is more resilient to disease attack and less liable to plant stress.

Thatch (especially spongy thatch, rather than fibrous thatch) is a common problem in turfgrass environments and can contribute to moisture retention, reduced root growth to depth and reduced air exchange within the soil profile.

Keeping the surface aerated, scarified, verticut and groomed will encourage easier airflow between grass blades, consequently reducing the potential for disease attack. [6] [7]

o Mowing:
Defoliation and a reducing height of cut, as well as increasing mowing frequency, have been shown to have a significant effect on root growth, in particular root biomass and thickness of roots. The lower the height of cut the shallower the root growth, the less root biomass is present and the roots are thinner. In addition, close cutting of a sward will typically produce a denser surface, which is ideal for sports such as golf and bowls, however, this does result in an increased relative humidity between the grass blades. All of these conditions increase the susceptibility of the grass to disease because you are stressing the grass plant, and often unnecessarily. [8] [9] [10]

Pest management
For convenience, pests can be sub-divided according to their size: smaller soil dwelling insects and creatures, or larger mammals and birds. The type of control methods can vary considerably depending upon the category of pest being managed.

The main smaller turfgrass pests are leatherjackets, chafer grubs and earthworms. [11]

Ants and nematodes are a lesser problem, but can be locally significant. An understanding of the lifecycle of these smaller pests is essential if effective control is to be undertaken.

The aim would be to (a) reduce the ground and environmental conditions which favour a pest and (b) control the pests when they are at their most vulnerable in their growth and development stage.

The main larger turfgrass pests are moles and rabbits, although foxes, birds and deer can be locally significant. Getting to know the habitats and habits of these animals can help in devising control methods that range from discouraging them, to humanely (although this might be considered an oxymoron) killing them.

Using maintenance activities to control pests: Earthworms
The conditions that are favourable to earthworm surface activity can be identified and then addressed to make them less favourable. [12] [13]

Several maintenance activities can be used to influence the production of an environment that is less attractive to earthworm activity, including:

  • Box off clippings to remove a potential earthworm food supply;
  • Consider reducing the use of organic fertilisers (although this may be a conflict with the aims of a sustainable turfgrass surface); A more appropriate approach may be to ensure organic fertilisers are not applied either too early or too late in the growing season, as this is when earthworm surface activity can be high;
  • Apply acidic top-dressings and fertilisers; being careful not to over acidify the soil surface to the detriment of the grass sward;
  • Remove thatch accumulation by hollow-tining (if a severe thatch build-up is present) and other aeration methods;
  • Do not apply lime unless essential;
  • Reduce reliance on fertilisers which produce an alkaline soil reaction;
  • Test the pH of irrigation water; counter measures will need to be taken if it is alkaline;
  • Regular drag brushing and switching to disperse earthworm casts to maintain playability.

The maintenance activities of aeration and thatch reduction will also reduce the level of protection offered to grubs during the winter months by increasing their exposure to cold weather.

Leatherjacket and Chafer grub control
I’ve written a blog on ‘Leatherjackets in your turf – Don’t panic’ (November 2017), which looked at how a well developed root system can act as an insurance policy against a low to mild attack of grubs, without the need for any chemical control (mind you there’s currently just one artificial chemical now available and only until 30th September this year, as it stands at the moment anyhow).

Read the article now: >>

Leatherjackets in your turf – Don’t panic

For these grubs the aim will be to keep thatch levels down, reduce moisture content of the soil profile during the late summer to ideally dessicate any eggs laid, and to keep the surface open with aeration over the autumn to early winter (if ground conditions permit) to aid cold weather penetration into the soil profile to stress the young grubs.

The focus is always on minimal to zero use of pesticides if we are to go ‘Beyond IPM’, so from a sales of products perspective this approach is not helpful as consumption of pesticides and potential profits will be significantly reduced.

The final part of this series will look at weed management and provide a conclusion for the series.

References

[1] Raikes, C., Lepp, N.W. & Canaway, P.M. (1996) ‘An integrated disease management (IDM) strategy for winter sports turf’, The Journal of the Sports Turf Research Institute, Vol. 72 1996, pp72-82

[2] Mann, R.L. (2004) ‘A review of the main turfgrass diseases in Europe and their best management practices at present’, Journal of Turfgrass and Sports Surface Science, Vol. 80 2004, pp19-31

[3] Beard, J.B. (1973) ‘Turfgrass: Science and Culture’, Prentice-Hall, p576

[4] Smith, J.D., Jackson, N. & Woolhouse, A.R. (1989) ‘Fungal Diseases of Amenity Turf Grasses’ (Third Edition) E&F.N. Spon Ltd, pp3-6

[5] Smith, J.D., Jackson, N. & Woolhouse, A.R. (1989) ‘Fungal Diseases of Amenity Turf Grasses’ (Third Edition) E&F.N. Spon Ltd, pp7-13

[6] Juska, F.V., Cornman, J.F. & Hovin, A.W. ‘Turfgrasses Under Cool, Humid Conditions’, in Hanson, A.A. & Juska, F.V. (Eds) (1969) ‘Turfgrass Science’ p501

[7] Shildrick, J.P. (1985) ‘Thatch: A review with special reference to UK golf courses’, The Journal of the Sports Turf Research Institute Vol.61 1985, pp8-25

[8] Troughton, A. (1957) ‘The Underground Organs of Herbage Grasses’, University College of Wales, Commonwealth Agricultural Bureaux, pp94-102

[9] Beard, J.B. (1973) ‘Turfgrass: Science and Culture’, Prentice-Hall, pp384-390; 580-581

[10] Parr, T.W., Cox. R. & Plant, R.A. (1984) ‘The effects of cutting height on root distribution and water use of ryegrass (Lolium perenne L. S23) turf’, The Journal of the Sports Turf Research Institute Vol.60 1984, pp45-53

[11] Mann, R.L. (2004) ‘A review of the main turfgrass pests in Europe and their best management practices at present’, Journal of Turfgrass and Sports Surface Science, Vol. 80 2004, pp2-18

[12] Kirby, E.C. & Baker, S.W. (1995) ‘Earthworm populations, casting and control in sports turf areas: A review’, Journal of the Sports Turf Research Institute, Vol.71, pp84-98

[13] Mann, R.L. (2004) ‘A review of the main turfgrass pests in Europe and their best management practices at present’, Journal of Turfgrass and Sports Surface Science, Vol.80, pp2-7

Chris Gray, 25th August 2018