Winter is coming!
As we head into the autumn/winter season, one of the major challenges turfgrass managers in temperate climates face on their playing surfaces, is infection by the pathogen Microdochium nivale. Commonly referred to as Fuzz, Fusarium patch, Microdochium patch and Pink Snow mould, Microdochium nivale infects most cool season turfgrass species, with infection primarily occurring under moist conditions below 18° C, with optimum occurrence between 0°and 6°C. The source of infection, the conidia and hyphae can lie dormant in organic matter and thatch until dormancy is broken by environmental changes, allowing for germination and growth. This ability to remain dormant for long periods is significant for turfgrass management, as ensuring low levels of organic matter will reduce the source of Microdochium inoculum. When environmental conditions are conducive, the conidia germinate and/or the hyphae commence growth and begin the infection process. Hyphae will grow over the sheath on to the leaves, and can be observed as pinkish/white mycelium, especially in early morning. Infection occurs via stomatal penetration. Once inside the leaf, hyphae will extend, via intercellular spaces, before penetrating the cells, extracting nutrients, causing loss of turgor, discoloration and collapse.
This is when disease symptoms are clearly observable on the playing surfaces. The hyphae continue to grow, then exit, via the stomata, releasing numerous conidia, which are disseminated by natural means but also by golfers and maintenance equipment.
Concisely, the pathogen wants to get into our turfgrasses, extract nutrients, exit and reproduce!
- Hyphae/conidia are the main source of inoculum.
- Environmental conditions allow infection to commence.
- Mycelium grows from the base of the plant.
- Infection by means of stomatal penetration
- Infects the plant extracting nutrients.
- Exits plant producing conidia which are disseminated.
Controlling Microdochium nivale Infection
Integrated Pest Management (IPM) techniques are best employed, comprising of establishing disease threshold levels, intensive field monitoring, good record keeping, awareness of climatic conditions, and most importantly, utilisation of non-pesticidal disease control strategies. Fungicide use is the last step in the IPM process.
Non-Pesticidal Disease Management
A key component of non-pesticidal disease management is the use of the ‘Disease Pyramid’. This is used to identify and influence the factors which combine to determine the level of disease incidence and severity.
There are four interacting factors:
- Host Plant
- Pathogen
- Environmental conditions
- Time
Host Plant
The sward composition in your site has a significant impact on the level of disease incidence. Poa annua is more susceptible to Microdochium nivale than Agrostis spp or Fescue, so it makes good sense to consider species conversion, or to increase percent composition of the less susceptible species at your site. There is increasing availability of new, more disease-resistant cultivars and improved methods of interseeding now available. Turfgrass® will advise you on how to proceed in this area.
The Pathogen
The inoculum of Microdochium nivale, is in the soils, the thatch layer and the general environment, and unfortunately there is little we can do about that. But conducive environmental factors are crucial for a disease outbreak, and thankfully we can do a lot in this area.
Environmental Conditions
Influencing environmental factors not only means weather/climatic conditions, but also the growth environment, and how nutritional and maintenance programmes can be used to reduce disease pressure. Plants, including turfgrasses, have evolved complex defense mechanisms to protect themselves from pathogens. They must first recognise they are under attack and this involves elicitors. They then produce short term responses aimed at containing the infection. They will produce antimicrobial compounds (like anti-bodies) which will directly inhibit the pathogen. Plants then use signaling compounds, such as Salicylic acid, which can lead to Systemic Acquired Resistance, i.e., resistance to the pathogen in uninfected parts of the plant and be primed to fight off any following infections. This is the time factor of the Disease Pyramid. We must slow the infection process but speed up the plant’s defence response.
There are no free lunches though, defences require generation of numerous compounds, and the plants need the reserves to produce them. This is where an autumn/winter programme of cultural procedures and targeted nutrition can play a significant role.
Cultural and Nutritional Controls
Leaf Wetness/Dew Management
Research has shown the significant impact leaf wetness duration has on Microdochium infection. Microdochium is most likely to occur when leaf wetness is maintained for 24 hours or more. All steps should be taken on turf surfaces to remove dew and maintain a dry surface during times conducive to Microdochium development, as this will slow the infection process.
Dragging/Switching the turfgrass surfaces are simple methods for removing dew and their impact on disease can be significant. The use of ‘dew dispersal’ surfactants can also be effective at reducing disease incidence, as results from the STRI have shown. While these products are effective, the longevity of their impact will vary with product, turfgrass growth and environmental conditions.
Maintaining good air movement is crucial, (chainsaws are useful tools!). Prune anything that limits light, as the sun angles decline during autumn. Apart from helping to maintain drier surfaces, light levels have an important impact not only on turfgrass quality but is vital for the acclimation of turfgrass to winter stresses. Inadequate light leads to weakened swards, poor root systems, and reduced reserves of energy, making them more susceptible to disease!
Mowing Heights
Raising mowing heights can help considerably. This increases leaf area and net photosynthesis, allowing turfgrass to generate and store carbohydrates necessary for defence compounds. Soil N levels can be high in late summer and a spike in growth can rapidly deplete carbohydrate reserves leaving levels dangerously low. If carbohydrate production outpaces carbohydrate use, then reserves will increase.
Rolling
To help maintain acceptable playing standards, lightweight rolling can be incorporated into your maintenance programme. This will have a combined effect of removing dew, maintaining playing quality and, as research from Oregon State University has shown, regular rolling will significantly reduce Microdochium infection.
NUTRITIONAL INPUTS
Nutritional programmes play an important role in combating Microdochium infection. Nutrition at this time of year should be geared to providing growth and recovery through the autumn/winter season and building carbohydrate reserves. Apart from supplying nutrition, many elements and compounds have a direct effect on suppressing Microdochium.
Ferrous Sulphate
Ferrous Sulphate has long been used to ‘harden’ turfgrass and improve colour, but does it suppress Microdochium? There are several studies showing that whether applied as Ferrous Sulphate Heptahydrate, or as a chelated liquid form, it will help suppress this disease.
Manganese and Zinc
Combinations of Manganese and Zinc are increasingly used in autumn/winter programmes and this is not surprising. These elements serve as activators for several enzymes that lead to production of defence related compounds.
Sulphur and Copper
Sulphur has been shown to suppress Microdochium patch on bentgrass as far back as 1975. More recently in Oregon State University, Sulphur applied monthly, significantly reduced Microdochium infection and reduced the number of fungicide applications required. Copper has been used to control disease as far back as the 19th century and has proven effective in combination with Sulphur.
Calcium
One of the key roles Calcium plays is as a component of the ‘Ion Flux’ which is part of the first defence responses to infection. Calcium can be relatively immobile once absorbed into the plant, so ensuring there is a readily available supply is vital.
Silica
Silica has both physical and biochemical effects on disease suppression. Deposition in the plant following foliar application will inhibit cell penetration and slow the infection, allowing time for defence induction. Biochemically, Silica can also enhance defence-related activation.
Defence Activators
In a similar manner to Silica, other compounds which could be included in the autumn/winter programme can be classed as ‘Defense Activators’. These, when used prior to onset of infection, can prime or enhance the turfgrass defences.
Chitin
Chitin is a primary component of the cell walls of fungi. During infection, fragments of the fungal pathogen – Microdochium can break off and act as elicitors, initiating defence inducement. By applying Chitin containing products, the plants can be stimulated to begin defence activation.
Salicylic Acid
Salicylic acid is a key signalling compound leading to systemic resistance. In a similar way to Chitin, pre-treatment with Salicylic acid can kick start defences, acting in a similar way as a vaccine for us humans.
Phosphite
Phosphorus, a major plant nutrient is taken up by plants as Phosphate (PO4) and is vital for numerous metabolic processes. Phosphite (PO3) is very similar chemically but has one less Oxygen molecule and does not provide any nutritional value. Published research, however, shows Phosphite not only directly inhibits Microdochium, but primes turfgrass defences, reducing infection by 60% compared to controls.
An important point to note is that while the above factors individually will have some effect on Microdochium, it is only when you start combining them that you will see significant effects.
A programme containing Phosphite, Calcium, Salicylic Acid, Manganese, Zinc Sulphur and Chelated Fe suppressed Microdochium incidence by 72% compared to controls.
Research from Oregon State University shows significant Microdochium suppression by Sulphur, Phosphite (KPhite) and rolling, with full control by combination of all three.
Research results from 2020/2021, containing a combination of Phosphite with a Copper based pigment and Phosphite with Manganese, Zinc, showed consistent suppression of Microdochium throughout the season, with a mean suppression rate of 76% compared to Controls.
CHEMICAL CONTROLS INPUTS
Chemical plant protectants are an integral but final step of IPM. Most available fungicides these days are systemic and to be effective, they need to be applied prior to any disease symptoms developing. Preventative applications of these fungicides can provide good control of Microdochium, and while the efficacy and safety of these products is not disputed, their use can give rise to several contentious issues. These include adverse public opinion due to the perception of high frequency of use, associated costs of chemicals, possible inhibition of non-target beneficial microorganisms, development of fungicide resistant populations, and the severity on restrictions and availability of fungicides. This makes the options of non-pesticidal controls ever more attractive.
PUTTING IT ALL TOGETHER
Ensuring good plant health and managing conditions conducive to Microdochium infection is the key for successful non-pesticidal control of Microdochium. Disease control is best implemented by means of IPM and using the Disease Pyramid to influence the factors conducive to infection. Starting from the end of summer, ensure all environmental pressures are reduced as much as possible. Control of growth rates are required to conserve plant carbohydrate stores, achieved by increasing mowing heights, balanced nutrition and PGR applications.
KEY POINTS
Influence all factors which reduce the microclimate conducive to Microdochium development.
- Dew removal is vital as extended periods of leaf wetness is a key factor for infection.
- Increasing air movement through tree management will also help.
- Late season aeration operations and topdressing can create the ideal microclimate for infection. If possible, try to complete prior to autumn. Bear in mind however, that thatch reduction will help reduce inoculum sources.
- Raise height of cut, turfgrass needs to generate and store energy for defences.
- Incorporate rolling as much as feasible into the programme.
- Nutritional programmes to include compounds such as Phosphite, Manganese, Zinc, Sulphur, Salicylic acid, and Fe as part of balanced, sequentially applied nutritional treatments.
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