Navigating turfgrass diseases
Drafting a concise article on turfgrass diseases in the United Kingdom is challenging due to the topic’s extensive scope and numerous variables.
Leaf spot infected Perennial Ryegrass at 40x magnification.
This article aims to offer clear and practical insights, serving as an introductory overview for those new to understanding turfgrass diseases or as a refresher for seasoned professionals, although it does not encompass every aspect or claim to be exhaustive in its coverage.
Defining Turfgrass Diseases
Turfgrass diseases are symptoms and signs indicating that the turf is damaged, typically due to an infection by a pathogenic agent. These pathogens, which can be viral, bacterial, fungal, oomycetes, algal or nematodal, are parasitic and antagonistic, harming the turfgrass while completing their lifecycle. As microscopic organisms, these are difficult to identify until the symptoms on the turf are presented. At times, an identification may only be determined by microscopy or more accurately by DNA-analysis. Apps on mobile devices are emerging with functionality to assist turf managers potentially identify and predict disease onset. Although fungal pathogens are the most common concern, nematodes, bacteria and oomycetes can also damage turfgrass. It is important to note that not all these organisms are harmful; some have beneficial or mutualistic relationships with turfgrass. Understanding these beneficial associations can be valuable in developing biological approaches to disease control too.
Impact of Diseases on Sports Turf
Turfgrass diseases can significantly affect the playing characteristics of sports turf by compromising the surface’s integrity. Diseases can cause issues ranging from root deterioration and thinning turf to large bare areas. For instance, root diseases like Take-All Patch and Pythium Root Rot, and foliar diseases like Red Thread and Microdochium Patch, can severely damage turf. Diseases often interact, such as Anthracnose with Microdochium Patch, and can be associated with pests or nutrient deficiencies. Some diseases, like Yellow Patch, may be unsightly but do not necessarily affect surface integrity. Understanding which diseases are most threatening helps in assigning prevention efforts.
Three Components of Disease
The onset of turfgrass diseases typically requires the interaction of three key components: a susceptible host, suitable environmental conditions and the presence of a pathogen. This “disease triangle” is fundamental in plant pathology. Environmental factors often include temperature, humidity, moisture, light availability, thatch conditions and pH levels. However, even with ideal conditions and the presence of a pathogen and susceptible host (turfgrass species), a disease may not always develop due to the complexity of nature and turf management.
Above, Fescue grasses withstanding infection of Take-All Patch fungal pathogen (Gaeumannomyces graminis). Mainly infected bent grasses dying off. An important disease to control on new root zone constructions.
Disease Transmission and Prevention
Pathogens can be transmitted through water, plant and soil material, machinery, equipment, footwear and even on the seed coat. Some pathogens remain dormant in the soil or thatch layer for seasons, striking when conditions are favourable. Understanding the susceptibility of different grass species to specific pathogens is crucial for disease prevention. Many turfgrass pathogens are host-specific, infecting only certain grass species. For example, Take-All infects Bentgrass roots but not Fescue.
Breeders have developed varieties within species with genetic resistance to certain diseases, enhancing disease prevention efforts. Prevention starts with this type of biological genetic selection of resistant grasses. This information is freely available through independent guides (e.g. British Society of Plant Breeders Turfgrass Buyers Guide, turfgrass-list.org and ntep.org), although not all varieties are easy to find or are listed.
Red Fescues and Perennial Ryegrass appear to have become increasingly susceptible to Red Thread (Laetisaria fuciformis). Once a minor issue, this progressive disease has risen in both prevalence and severity. Management typically involves applications of nitrogen fertiliser and measures to prevent drought, followed by systemic fungicide treatments if necessary.
Further to this, there are cultural and other biological measures to prevent disease. Mainly this involves managing conditions associated with disease outbreaks, such as removing decaying plant material (e.g. thatch removal), improving drying conditions of the turf environment (e.g. subsurface and surface aeration and airflow/movement in the microclimate), using appropriate seeding rates at establishment, controlling irrigation to avoid over- or under-watering, and managing fertiliser inputs to avoid excessive or inadequate inputs for optimum turfgrass health. Certain micronutrients may assist in controlling diseases, e.g., iron for Microdochium Patch and manganese for Take-All suppression.
Physical activities can influence disease onset, for example, poor quality of cut may lead to disease. Interestingly and counterintuitively, physically rolling fine turf has been shown to reduce the onset of Anthracnose disease too. Biological control of pathogens is a growing area, with beneficial bacteria like Bacillus spp. and beneficial fungi like Trichoderma spp. known to suppress a range of fungal pathogens. These may be applied on to the turf as a spray or in a granule/powder form. The success of this type of inoculation is an area for further investigation, as this may be site-specific.
Disease infection at a poorly cut leaf blade of Perennial Ryegrass. Highlights the importance of cut quality to prevent infection.
It’s worth repeating, these are regarded as preventative and not immediate curative solutions when symptoms are present. The use of a fungicide may offer a comparatively efficient effect, especially when planned correctly, however, their use should not be relied upon. A mix of all these approaches, or ‘integrated’ approach, is advisable with the use of a fungicide when the pathogen is present or at least strongly forecasted, based on disease pressure.
Fungicides
Fungicides have been an effective and a cost-efficient method for maintaining high-quality turf surfaces, providing assurance and a high level of control. There are multiple application methods and modes of action (time of year). The use of ‘preventative’ fungicides relies on application at early onset or based on disease pressure predictions (e.g. a disease model). The timing of application and accurate identification of target disease to label listing is critical for optimal control. The use of ‘curative’ fungicides does not recuperate tissues (leaves, roots, shoots) to become healthy; they protect uninfected tissues from further infection. Curatives are typically higher in concentration or applied at shorter intervals.
DNA-analysis from an established Perennial Ryegrass Pitch without symptoms. Presence of four pathogens identified for preventative management.
The main two modes of action are contact and systemic. Contact fungicides simply coat plant tissues and protect against infection, these are also known as ‘protectants’. Systemic fungicides penetrate into the plant and also known as ‘penetrants’. Penetrants move within the plant, typically in the transpiration system, upward in the xylem tissues. Further to this, there are also local-penetrants that pass through plants tissues (translaminar). Fungicide use is increasingly scrutinised due to environmental and societal concerns, and reducing the applications of fungicides is widely acknowledged as a key turning point in sustainable turfgrass management. Disease resistance is a risk that further exacerbates the constraints of fungicide use, including difficulties with future efficacy. Manufacturers of fungicides and organisations such as the Amenity Forum invest heavily in research and education for operatives to perform best practices. It is highly advisable that these shared practices and educational updates are taken and utilised.
Conclusion
Effective management of turfgrass diseases involves understanding the disease triangle, modes of pathogen transmission and specific susceptibilities of grass species. Combining biological approaches, genetic resistance and judicious use of irrigation, fertilisers and fungicides can help maintain healthy turfgrass in the United Kingdom. Equally important is staying up to date with new and emerging advances in integrated disease management to ensure sustainable turfgrass management.
Author biography
Dr. Jonathan Knowles is the Head of Sports Turf Academy at Leicester City Football Club, where he spearheads initiatives in sports turf education, research and development. His role encompasses providing expert consultancy and advisory services in sports turf management. A focus of Dr. Knowles’ work is the advancement of sports turf education, with a particular emphasis on turfgrass pathology and diagnostics. Through his leadership, the Academy aims to enhance the knowledge and skills of professionals in the field, promoting best practices and innovative solutions in sports turf management.