Summer is the turf managers busiest, most challenging but also often most satisfying season. It can bring long hours, high temperatures, drought, excessive growth and too many golfers, but also the satisfaction of presenting your course at its best!
Summer also brings with it one of the biggest challenges for turf managers, which is controlling summer diseases. Here in the UK, Ireland and many parts of Europe, the main summer disease is Anthracnose (Colletotrichum cereale), affecting mostly cool season turfgrass with Poa annua being very susceptible.
Figure 1: Anthracnose on a Poa annua golf green.
Anthracnose effects turfgrass in 2 forms:
- Basal rot, which affects the lower parts of the turfgrass plant, crowns, stem bases, and roots.
- Foliar blight is the second and leads to a yellowing of leaves and shoots having a similar appearance to drought stress in appearance.
Figure 2: Typical infection of Anthracnose on a golf green.
Figure 3: Anthracnose infection showing the blackened base of sheaths.
Infection occurs during early to mid- summer, during warm, wet periods over a range of temperatures. Symptoms of basal rot develop at cooler temperatures ( 15 °C to 25 °C) and foliar symptoms occur at temperatures above 26 °C. Continuous leaf wetness of 12 hours or more, and temperatures of 14°C to 28 °C are necessary for infection, which intensifies with increasing temperature and leaf wetness duration.
Figure 4: The Anthracnose infection cycle, over wintering as mycelium or conidia followed by infection under conducive conditions.
During infection, appressoria are formed which anchor the fungal filaments to the leaf surface. A penetration peg is formed and penetrates plant epidermal cells, closely followed by the production of infection hyphae. These hyphae then invade the surrounding plant mesophyll cells. Because it then is a necrotroph, it starts killing plant tissues with enzymes, as the hyphae continue to extend. Plants subjected to drought and/ or fertility stress are more susceptible to infection.
Figure 5: Anthracnose conidia, and conidia germinating on leaf to begin infection.
Whichever form Anthracnose takes, it is important to note that it is very much a stress- related disease. Physiological stress from any source greatly encourages the development and spread of Anthracnose. The most common sources are close mowing, drought stress, low fertility, excessive traffic, poor soil drainage or excessive thatch/ organic matter accumulations.
Best Management Practices
There are numerous best management practices which can be employed to reduce Anthracnose incidence. Key to this is to understand the conditions conducive for infection and to be successful ‘ know your enemy’! Identify the conditions which lead to infection and then influence these factors to minimise the challenge.
Thatch Control
Almost all turfgrass diseases are reduced by good thatch control. Excessive thatch/ organic matter provides an excellent incubation site for pathogens. The Anthracnose pathogen – Colletotrichum cereale can overwinter in the thatch layer, as mycelium or conidia derived from previously infected turfgrass tissue I t can also survive as darkly pigmented aggregates of hyphal cells ( stromata) that are formed at the base of tillers. Exposure of these stromata to sunlight and temperatures of 15 º C to 25 º C can induce the formation of conidia. The Anthracnose mycelium and conidia can lie dormant until conditions are conducive for infection, so thatch reduction = less inoculum.
Significant levels of thatch will also impact the overall health of the turfgrass, leading to a reduced ability to defend itself against not only Anthracnose, but any biotic or abiotic challenge.
Moisture management is crucial – poor irrigation practices can lead to increased disease problems. Avoid frequent, and/ or late evening irrigation that results in extended periods of leaf wetness and free moisture periods throughout the night.
Extended periods leaf wetness can also be caused by dew and guttation fluid. Pathogens such as Anthracnose need water for their development and disease pressures are accentuated by extended periods of free moisture. Reduce dew periods and consider allowing drying periods to disrupt the growth cycle of fungi favoured by free moisture.
On the other s ide of the moisture scale, research has shown that maintaining soil moisture levels at 80 % ET compared to 40 % ET, will contribute to less Anthracnose.
Regarding soil moisture, the implementation of a surfactant programme will provide a number of benefits. I t will ensure efficient water infiltration, reduce the danger of localised dry spots and will allow for greater consistency of rootzone moisture levels. All this will reduce turfgrass stress and less stress = less disease.
Cultural Control Practices
As already mentioned, Anthracnose is stress related, so any means of reducing stress will contribute to less disease – pretty much Greenkeeping 101 . Turf managers can employ numerous cultural practices which will have a significant impact on Anthracnose incidence. A programme which includes regular raising height of cut, lightweight rolling and sequential light topdressing has been shown to significantly reduce Anthracnose levels.
How does this work?
Research from Rutgers University in the US showed that raising mowing heights prior to, and during periods of disease activity have been shown to reduce Anthracnose development. Increasing the height of cut from 2. 8 mm to 3 . 6 mm significantly reduced disease incidence. To maintain playing standards, golf course superintendents can employ growth regulators and lightweight rollers to maintain desired putting speeds in lieu of low mowing heights.
Increased HOC equals less plant stress = less disease
Figure 6: Effect of increased mowing height from 2.8 mm to 3.6 mm on Anthracnose levels.
So, higher mowing heights, when taken in conjunction with regular rolling, will maintain greens speed and playability at an acceptable level.
But rolling also has supporting research data showing it to have a direct suppressive action on many turf diseases, including Anthracnose.
Rolling will reduce Anthracnose Incidence
Figure 7: Effect of lightweight rolling on Anthracnose incidence
Regular light sand topdressing is also part of the jigsaw of cultural control measures that
combine together to reduce Anthracnose levels. It does this by protecting the crowns of the turfgrasses, again less stress …. you know the rest!
Figure 8: Protection of crowns and sheaths of turfgrass by regular light sand topdressing.
Figure 9: Protection of crowns and sheaths of turfgrass by regular light sand topdressing.
While Cultural practices can be very effective in suppressing disease levels, the use of targeted nutritional programmes is also a key component in significantly reducing Anthracnose in turfgrass.
A balanced nutritional programme, tailored to the specific needs of the sports surface and nutritional status of the rootzone is a key factor in successful turfgrass management. Adequate fertilisation is essential to Anthracnose management.
Here are some examples:
Deficiencies of any essential plant nutrient will impede growth and increase Anthracnose pressure. Ideally, tissue samples should be analysed for nutrient content on a regular basis to ensure that all nutrients are present in adequate amounts.
However, apart from supplying essential nutrition, many nutritional inputs also have added benefits and can significantly suppress Anthracnose incidence in turfgrass!
Here are some examples:
Nitrogen fertility is the single most important factor in managing Anthracnose. Light, frequent applications of nitrogen fertiliser will reduce disease severity and aid recovery from disease-related injury, provided turf is not over stimulated during periods of heat stress. The data show spoon-feeding during periods of high Anthracnose pressure will reduce disease levels.
Potassium levels maintained at a minimum 35 ppm is essential in reducing Anthracnose pressure.
Copper and Sulphur have been used as fungicides for centuries and can be very effective, especially when combined in a programme with other elements.
Silica, when applied as a foliar treatment, can strengthen plant cell walls, reducing pathogen regression.
Phosphite has much data to support its efficacy in reducing numerous turfgrass diseases including Anthracnose.
Manganese and Zinc activate key enzymes vital for turfgrass defence responses.
Salicylic Acid is the most important signalling compound for initiation of Systemic Acquired Resistance in turfgrasses.
All the above will have some effect on Anthracnose, but it is only when you start combining them together in a nutritional program that you will see very significant disease suppression results.
Research in the USA and Ireland confirms this, with conclusive evidence showing that
combining the above elements will not only significantly suppress Anthracnose, but also lead to enhanced turfgrass quality when compared to untreated controls.
Results from trials carried out in Ireland during the summer of 2018,clearly show the positive effects of nutritional inputs on levels of Anthracnose in Poa annua greens surfaces.
The treatments were applied bi-weekly, aswell as spoon-feeding Nitrogen and Potassium, including Calcium, Sulphur, Copper, Manganese and Zinc, which are all important for disease suppression. The Polyphosphite is proven to prime defence responses in turfgrass. There was a surfactant included in the programme and this reduced drought stress, but also solubilised locked-up Calcium, which plays a crucial role in early defence responses.
Salicylic Acid was in the programme and this stimulated Systemic Acquired Resistance, which strengthens cell walls and can slow the ingression of pathogens.
| Treatments | Application timing |
| (1) Untreated Control | 14 days |
| (2) Polyphosphite | 14 days |
(3) Nutritional program: NPK, Calcium, Sulphur, Copper, Manganese, Zinc, Polyphosphite, Salicylic acid, Silica, Surfactant | 14 days |
| (4) BannerMaxx | 14 days |
Table 1: Treatments and application intervals.
This programme reduced Anthracnose by supplying adequate and balanced nutrition, primed and enhanced the plants natural defences, stimulated systemic acquired resistance and reduced drought stress.
Figure 10: Treatment effect on percent Anthracnose incidence on trial plots (n=6). Mean values from 6th August to 21st September 2018.
Bars indicate 95% confidence intervals; letters indicate statistical differences a determined by Tukey post hoc analyses at a significance level of p = 0.0 5.
The programme in a nutshell produced:
- Less stress = less Anthracnose.
- Availability of elements shown to reduce disease incidence.
- Primed and enhanced plant defence responses.
An important secondary result from the trial showed that the treatment programme produced a higher quality of turf due to the range of nutritional inputs, wetting agents and polyphosphite. So as well as suppressing Anthracnose to the same level as a bi-weekly fungicide programme, the nutrient programme provided a significantly better turfgrass quality.
Figure 11: Treatment effect on mean levels of turfgrass quality (n=6). Data are mean values from August to September 2018.
Bars indicate 95% confidence intervals; letters indicate statistical differences as determined by Tukey post hoc analyses at a significance level of p = 0.05.
Chemical Controls
Obviously having a fungicide programme in place (if you are lucky enough to have chemicals legally available) and labelled for the control of Anthracnose, is a good option.
There are a number of fungicides from varying chemical groups currently labelled for Anthracnose control (this list could vary according to your geographic or legislative area). These include Heritage Maxx (Azoxystrobin), Medallion TL (Fludioxonil), Instrata Elite (Difenoconazole/Fludioxonil), Ascernity (Difenoconazole/Benzovindiflupyr) and Inter Tebloxy (Tebuconazole/Trifloxystrobin).
Remember, however that repeated use of fungicides with similar modes of action or with a single action site, can result in increased resistance to the fungicide. There are several practices that will impede the build-up of resistance:
- Use contact fungicides alone or in combination with systemics as part of the control programme.
- Use fungicides on a preventive, rather than a curative, basis.
- Rotate or mix systemic fungicides with different FRAC codes. Repeated use of the same or a similar fungicide selects resistant members of the population.
- Do not rely on fungicides alone. Combine fungicide use with cultural practices that reduce disease severity.
That final point is significant, especially when managing turfgrass with limited or no availability of fungicides. As already mentioned, there are many options available to turf managers to prepare their turfgrasses to be better able to withstand the Anthracnose challenge, and importantly these options will also complement and enhance any fungicide programmes you may be running.
Fungicides are most effective when combined with cultural and nutritional practices that reduce plant stress and prime them to withstand challenges!
So the key points to consider in order to control Anthracnose:
- Know your enemy!
- Influence as many factors that contribute to conducive conditions for this disease.
- Employ cultural practices which will enhance the ability of your turfgrass to withstand pathogen challenges.
- Employ a balanced nutritional programme. Avoiding deficiencies in nitrogen and potassium are critical to reducing anthracnose severity, and include the elements and compounds above which have been shown to have suppressive properties.
- If available, include a fungicide programme suitable for Anthracnose, but remember to use best management practices to avoid possible resistance build-up.
- Fungicides are most effective when combined with cultural and nutritional practices that reduce plant stress and prime them to withstand challenges!
About the Author
DR JOHN DEMPSEY
Technical Advisor To Turfgrass
John has 40 years of greenkeeping experience. He was Superintendent of I reland’ s oldest golf course – The Royal Curragh from 1993 to 2019 . His academic qualifications include a 1 st Class Honours Degree in Turfgrass Science and a Ph D in Plant Pathology at the University of the West of England, Bristol.
John has conducted independent research on turfgrass disease management for the past 15 years and has headed independent Turfgrass Research s ince 2019 .
Research interests have extensively covered the subject Microdochium nivale , turfgrass responses to biotic and abiotic challenge and the effect of nutritional programmes on disease suppression, turfgrass growth and quality.
John has presented the results of his research at numerous conferences in I reland, Scotland, France, Germany, Norway, Canada, Sweden, Czech Republic, and at GIS in the USA and BTME in Harrogate, UK.
Email: drjjdempsey@gmail.com