Shady Business

Turfgrass expert and Australian Turfgrass Management columnist John Neylan looks at the effects of shade in high maintenance Turfgrass 

Providing there is an adequate turf maintenance programme in place, the surrounding environment has the greatest impact on the performance of turfgrasses prepared as golfing surfaces. To maintain healthy turfgrass on greens, tees and fairways, it is critical that they receive adequate sunlight and air movement. If either component is lacking, turf quality will be compromised. 

Golf greens are the most intensely maintained turf areas on the golf course, however, even well-constructed putting greens with the best turfgrass varieties will struggle under low light, poor air movement and high humidity. In order to provide a high quality playing surface for golf, a healthy and robust turfgrass sward has to be established and maintained. 

 

A key element for any healthy turfgrass is that it must receive a certain quantum of sunlight each day. The quality and quantity of light the turfgrass receives is essential for the process of photosynthesis, which converts light energy into chemical energy and then storing the energy as sugars for the plant’s growth and health.

Strong growth and good plant health is essential for turfgrasses to withstand the low cutting heights, frequent mowing and the regular rolling required in the preparation of high quality golfing surfaces, in particular putting surfaces.  Good plant health and growth is also essential for the turf to recover from wear. 

Traditionally, it has been considered that the most critical time of year for providing sufficient light is during the months of May to late September. For optimum creeping bentgrass (Agrostis stolonifera) growth and health during this period, the sunlight required for the photosynthesis process will be received at a minimum rate of 10-12 mol/m2/day.

However, recent research has indicated that even during mid-summer the turf requires a minimum quantum of light in order to grow and remain healthy (M. Richardson, 2017). 

Prolonged exposure to shade, or more specifically a lack of light, will weaken and potentially kill most turfgrass species and make it impossible to prepare year-round elite level putting surfaces. Because of the effects of shade and poor air circulation there is a greater requirement for inputs such as fungicides, insecticides, electricity (required to run fans) and the need for turf repair and/or replacement when the turf is damaged.

 

The effects of shade on turf

Trees are an integral part of most golf course landscapes in Australia and make a considerable contribution to their aesthetic beauty and playability. From an agronomic perspective trees are often considered to be just another ‘weed’, albeit a very large one, as trees compete with the turf for space, light and water. 

 

Prolonged exposure to shade, or more specifically a lack of light, will weaken and potentially kill most turfgrass species and make it impossible to prepare year-round elite level putting surfaces

   

The challenge is finding a compromise that fulfils the architectural requirements of using trees without having a negative impact on the agronomic aspects of growing high quality turfgrass and producing good playing surfaces. The biggest challenge with trees is understanding that they will continue to grow in height and width for 30-plus years which changes the local ‘environment’, including space, shade and air movement. In some situations, trees have come to overwhelm the course from an agronomic and playability standpoint, causing widespread turf problems and imposing restrictions on the original strategic intent of the golf course architect.

While trees decrease the amount of available light for photosynthesis, they also reduce air movement across the turf and increase the humidity in the turf canopy. During the summer months these conditions increase the heat stress on the turfgrass and increase the incidence of diseases and insect pests. 

Air flow helps cool the turfgrass canopy and is especially important for cool-season grasses during summer heat. It is important to note that a green that receives very good sunlight but poor air movement may still perform poorly.  Adequate light and good air movement are critical in the preparation of high quality turf surfaces. 

Shade on golf courses, in particular on bentgrass putting greens and warm-season grass tees, affects the turf in several significant ways including;
•    Moderated temperature (cooler during winter and hotter in summer);
•    Reduced wind speed (less air circulation and less drying);
•    Increased relative humidity;
•    Greater duration of leaf wetness;
•    Higher CO2 level;
•    Reduced growth rates; and
•    Reduced root mass.

Shade or low light affects the anatomical, morphological and physiological characteristics of the turf (Table 1) which in turn impacts how the turf is managed and the standard of the playing surface (Fry and Huang, 2005). The impact on turfgrass surfaces are;
•    Accelerated turf thinning;
•    Reduced turf recovery from wear;
•    Increased disease;
•    Increased moss and algae;
•    Increased presence of weed species such as Poa annua; and 
•    Overall deterioration in surface playability and presentation.

 

Table 1:      Anatomical, morphological and physiological effects on turfgrasses (1)

 

EFFECTS

 

MANIFESTATIONS

Anatomical
•    Thinner cuticle
•    Fewer chloroplasts
 
  •    The turfgrass plants have reduced photosynthesis.
•    The turf has slower recovery from wear and other stresses such as pests and disease.
•    The plant is weakened and less tolerant to wear and invasion by disease. 
•    The playing surfaces tend to have a thinner turf cover.
 
Morphological
•    Thinner, narrower leaves
•    Longer leaves and internodes
•    Lower shoot density
•    More upright growth
 
  •    The turfgrass plants tend to produce more upright growth and there is reduced turf density. The main impact is that the putting surface is not as tight and smooth compared to greens in an open position.
Physiological
•    Higher chlorophyll content
•    Greater production of gibberellic acid
•    Lower photosynthetic rate
•    Lower respiration rate
•    Lower transpiration rate
•    Greater succulence
•    Lower carbohydrate reserves
 
  •    The turfgrass has a reduced ability to grow and recover from the frequent mowing and preparation required for high level golfing surfaces and in particular greens.
•    The turf will be softer which results in greater pitch mark damage.
•    The succulent turf is also more susceptible to the infection from diseases.
•    Reduced root system which decreases the ability of the turf to tolerate periods of high temperatures without frequent irrigation. 
 
1 Fry, J., and B. Huang. 2005. Applied Turfgrass Science and Physiology. New Jersey: John Wiley & Sons. Pp. 111-123.