Building defenses against summer diseases
We’re now heading into the turf managers busiest, most challenging, but also often most satisfying season …Summer. It can bring long hours, high temperatures, drought, excessive growth, too many golfers to fit in the day, but also the satisfaction of presenting your course at its best!
Summer also brings with it one of the biggest challenges for turf managers, that is controlling and suppressing a wide range of summer diseases. The scope and range of diseases vary with the geographic area and climate. Here in Ireland and the UK, the main summer disease is Anthracnose (Colletotrichum cereale), with less problematic infections of Red Thread (Laetisaria fuciformis) and Fairy Ring (numerous Basidiomycetes), but also there are increasing problems with Dollar Spot (Clarireedia homoeocarpa).
In areas with less temperate climates, i.e. US and Canada for example, the range of summer diseases is much more varied, and along with Dollar Spot and Anthracnose includes Brown and Yellow Patch (Rhizoctonia spp.), Grey Leaf Spot (Pyricularia grisea), Pythium (Pythium spp), Summer Patch (Magnaporthe poae), Waitea Patch, Brown Ring Patch (Waitea circinate) …. a veritable turfgrass pathologist’s dream!
Whichever pathogen turf managers are facing there are a number of options available to them in order to prepare for the challenges.
Obviously having a fungicide program in place (if you’re lucky enough to have chemicals legally available) suitable for the range of pathogens you’re dealing with is a good option.
Remember 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 buildup of resistance.
- Use contact fungicides alone or in combination with systemics as part of the control program.
- 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. There are many options available to turfmanagers to prepare their turfgrasses to be better able to withstand disease challenges, and bear in mind these options will also complement and enhance fungicide programs you may be running.
- Fungicides are most effective when combined with cultural and nutritional practices that reduce plant stress and prime them to withstand challenge!
Key to this is to understand the conditions conducive for what ever pathogens you have to contend with – know your enemy! Identify the conditions which lead to infection and then consider the Disease Pyramid and influence these factors to minimise the challenge.
There are numerous practices we can employ to prepare or turfgrass for summer challenge:
Almost all turfgrass diseases are reduced by good thatch control, excessive thatch provides an excellent incubation site for pathogens, and also inhibit the overall heath of the turfgrass leading to a reduced ability to defend itself.
Nutritional programs need to be judiciously applied as excessively high or low fertility can contribute to disease pressures, a careful balance is required.
High nitrogen levels increase the susceptibility of cool-season grasses to leaf spot, Rhizoctonia brown patch and Pythium blight.
Low nitrogen levels increase turfgrass susceptibility to Dollar Spot and Red Thread.
Low potassium levels in the soil reduce turfgrass tolerance to high temperatures and drought stress, which can increase the potential of diseases such as summer patch.
Low pH is often associated with diseases such as Brown Patch.
Some elements and compounds can have a direct effect on a plant’s response to pathogen challenge. Defense Activators for example, are compounds used prior to infection that can prime turfgrass defences leading to Systemic or Induced Systemic Resistance and are increasingly forming part of disease control programs.
- Ferrous sulphate has been used by generations of greenkeepers to ‘harden the turf’, and studies have shown it effective at reducing disease levels.
- Copper and Sulphur have been used as fungicides for centuries and can be very effective, especially when combined in a program with other elements.
- Silica, when applied as a foliar treatment, can strengthen plant cell walls reducing pathogen ingression and has been shown to promote numerous other beneficial responses.
- Phosphite has much data to support its efficacy in reducing numerous turfgrass diseases.
- Manganese activates several enzymes essential for the generation of secondary metabolites vital for the plants’ defence against numerous stresses.
- Chitin is a primary component of the cell walls of fungi and when applied can act as an elicitor initiating defence inducement.
- Salicylic acid is a key signaling compound leading to Systemic Acquired Resistance in plants and is coming under increasing scrutiny as an elicitor of these defences in turfgrass.
Moisture management is crucial, improper irrigation also can lead to increased disease problems. Avoid frequent, and/or late evening irrigation that results in extended periods of leaf wetness and free moisture period throughout the night.
Extended periods of leaf wetness can also be caused by dew and guttation fluid. Pathogens need water for their development and pathogens such as Pythium Blight, Brown Patch, and Dollar Spot are accentuated by extended periods of free moisture.
Consider allowing drying periods (near wilting) to disrupt the growth cycle of fungi favoured by free moisture.
Combining these practices can have a synergistic effect and significantly reduce disease incidence.
Two examples:
Anthracnose is very much a stress related disease, so any means of reducing stress will have a positive result. Cultural practices which include regular lightweight rolling, sequential light topdressing, raising height of cut, spoon feeding Nitrogen, e.g., 0.1 lb./M weekly, and maintaining adequate Potassium levels greater than 35 ppm can all combine to significantly reduce disease levels.
Dollar Spot is possibly the major summer disease turf managers in warmer climates have to deal with, again be aware of the conducive factors for infection and influence them. Some are out of our control e.g. high temperatures and humidity, but carefully planned nutritional inputs and soil moisture management and cultural practices such as rolling will contribute to significantly reduced infection levels.
Key Points:
- Know your enemy!
- Influence as many factors that contribute to conducive conditions for disease.
- Employ a balanced nutritional program suitable for your specific site environment and turf species and include some of the elements and compounds listed above which have shown to have disease suppressive properties.
- Employ cultural practices which will enhance your turfgrasses ability to withstand pathogen challenges.
- If available, include a fungicide program suitable for the pathogens most prevalent and be sure to use best management practices to avoid possible resistance buildup.
Have a great summer!
Dr. John Dempsey
Independent Turfgrass Research
Email: [email protected]
Web: https://orcid.org/0000-0002-4745-1541
