FAQs: Turfgrass heat stress, Turf Screen and related topics

How does Turf Screen work?
Heat tolerance in turfgrasses has been associated with the maintenance of transpiration and photosynthesis among various other mechanisms (Jiang, Y. and B. Huang, 2000, Effects of drought or heat alone and in combination on Kentucky bluegrass. Crop Sci.) Essentially, Turf Screen scatters UV light to reduce sunburn and keeps plants cooler by reflecting IR light.

Turf Screen improves the turf’s heat tolerance by reflecting 76% – 90% of harmful UV radiation to reduce sunburn. It also reflects heat-producing IR radiation, keeping the plant 7°—12° F cooler, which can improve water use, reduce the incidence of heat stress, and enable basic physiological processes to continue in high temperatures when turfgrass would normally shut down.

Plants exposed to too much heat and sunlight show reduced photosynthesis. Stomates on the leaf close when temperatures rise above certain thresholds. With stomate closure the plant takes in less CO2. When Turf Screen reflects away significant amounts of ultraviolet and infrared radiation, plants remain cooler, with stomates open for more hours per day. Therefore, more CO2 is taken into the plant for photosynthesis.

Tell me more about Turf Screen’s key ingredients
Titanium dioxide and zinc oxide are the workhorses in Turf Screen, although there are other carefully selected ingredients included in the formulation. Titanium dioxide is found in almost every personal protection sunscreen with a physical blocker because of its high refractive index and its strong UV light absorbing capabilities. It is also highly reflective of thermal IR (Blakey and Hall, 1988); by reflecting IR light the plants stays cooler, reducing heat damage.

Like titanium dioxide, zinc oxide also reflects infrared from the plant surface. Unlike titanium dioxide, it has a much higher ability to protect in the long UVA range (300 — 400 nm), and it absorbs rather than scatters most UVA. Thus, used in combination with titanium dioxide, zinc oxide “closes the window” in the UVA range. Zinc oxide complements titanium dioxide protective abilities and extends photoprotection where titanium dioxide needs reinforcement.

If Turf Screen blocks out harmful sun rays that cause sunburn and heat stress, won’t it also block most of the light required for photosynthesis?
Turf Screen does not limit a plant’s ability to photosynthesize or uptake nutrients and turf protection products. It is specially formulated to reflect harmful infrared and ultraviolet radiation from plant surfaces while allowing penetration of beneficial Photosynthetically Active Radiation (PAR). Turf Screen-treated plants are typically several degrees cooler than untreated plants and a cooler plant leads to reduced heat stress and more efficient water use, increased photosynthesis, and better turf quality.

Will Turf Screen be absorbed into the plant, possibly interfering with the plant’s biochemical processes?
Turf Screen is designed to stay attached to the turf’s exterior in order to reflect, absorb and filter solar radiation. Particular attention and engineering was paid to the particle sizes in Turf Screen — they are larger than the grass’ stomates in order to keep Turf Screen’s active ingredients from entering the plant through its stomates. Turf Screen does not block leaf stomates so gases (O2 and CO2) and water continue to move in and out of the plant, maintaining natural photosynthetic and cooling processes.

Can Turf Screen reduce watering needs?
Plants react to sun stress like humans. They perspire — a process called transpiration — which means the more temperatures rise, the more water they need . Turf treated with Turf Screen is cooler. By reducing turf temperature, the amount of water used for cooling by evapotranspiration is reduced, leaving more water available for keeping stomates open and allowing better leaf gas exchange. In effect, cooler turf uses available water more efficiently — less is used for cooling and more for photosynthesis. As a result, turf quality improves noticeably. Several superintendents have reported less time spent on irrigating and syringing during heat spells. Another benefit: going home an hour or two earlier rather than staying to syringe your greens one last time!

My club members appreciate anything we can do to reduce our environmental footprint. Can Turf Screen help make our operation more sustainable?
Turf Screen is made with all natural ingredients — nothing synthetic here. Since the turf treated with Turf Screen is healthier, it is more resistant to disease and other stressors, thus reducing the need for herbicides and pesticides. It also can cut watering needs. Plus, it’s safe — the active ingredients used in Turf Screen have been used for years in personal sunscreens that are applied daily to human skin.

What do other superintendents that have used Turf Screen have to say?
Scott May, superintendent at Manufacturers Golf and Country Club, PA for a decade, has been using Turf Screen for 3 years (267.246.8654). Scott would love to talk to you about his experiences, but even he admits he may be a bit biased since he invented Turf Screen and is the President of Turf Max, LLC, the maker of Turf Screen.
Check out Turf Screen’s website for comments and testimonial from a number of superintendents.

In addition, a few references to contact:

  • Scott Bordner from Rivercrest Golf Club, PA can be reached at 484.844.7317
  • Matt Willigan from Llanerch Country Club, PA can be reached at 610.724.5001
  • Matt Strader from Hidden Creek Country Club, Reston, VA at 717.496.3039

Sun and heat damage — an overview
In general, heat stress can be expected to occur when air and soil temperatures exceed 86°F for prolonged periods. When cool-season grasses are subjected to indirect heat stress, root and shoot growth decreases. Reduced growth is followed by root dieback, loss of turf vigor, density and green color, and possibly death of plants. High temperature stress also results in an increase in respiration and a decrease in photosynthesis.

Most turfgrasses have a built-in cooling system in the form of transpiration. During transpiration, energy is used to evaporate water from the leaf surface. In this process the leaf is actually cooled — so long as the leaf has open stomates which are actively transpiring, the temperature may not increase to a lethal level. However, should the stomates be closed due to a stress such as an internal plant water deficit, then transpiration will be impaired and lethal high temperatures may develop.

Carbohydrates are an important source of energy for sustaining shoot and root growth. The imbalance between respiration (use of carbohydrates) and photosynthesis (production of carbohydrates) during periods of heat stress results in a weakened ability of plants to repair themselves, particularly on putting greens.

When high temperatures and humidity place cool-season turf under significant heat stress plant tissue damage will occur.  Even if the turf looks healthy, heat and light stress can reduce or completely halt photosynthesis. Water stress is also intricately involved with heat and light stress. When soil moisture is limited, a plant’s ability to cool itself through transpiration is impaired. Stomata close and turf temperature increases. Ultimately tissue destruction and cell death occur.

Turf experiencing heat stress is more vulnerable to damage from other summer related stresses (e.g.; excessively close mowing, traffic and wear, warm weather fungal diseases, poor water quality, poor soil drainage, poor air movement, insect damage etc.). In other words, during a period of mid-summer heat stress the grass plants are more vulnerable to everything that can cause damage.

In addition, prolonged heat stress significantly increases soil temperatures, which greatly influence root growth, root health and function. High soil temperatures result in less root production, rapid root maturation and die back, and little production of new roots. Above ground the turf thins and individual plants become more spindly.

The primary mechanisms responsible for deteriorating turf quality from prolonged bouts of severe hot weather are:

  • Ultraviolet radiation penetrating and destroying the epicuticular waxes on the leaf-surface
  • Infrared radiation causing secondary epidermal damage
  • Infrared radiation also causing over-heating of the plant and resultant damage
  • Infection by secondary bacterial and fungal diseases, which is common in heat stressed turf

The sun’s heat damages turf in two general ways. One type is heat stress, which causes plants to respond by shutting down the photosynthetic process. Another type of damage is sunburn, which can cause physical damage to leaf surfaces and inhibit the photosynthesis and transpiration processes. While sunburn and heat stress are different, they both result from excessive exposure to ultraviolet and infrared light from the sun and can be equally devastating to turf quality. The key to reducing damage is lowering turf and root zone temperatures.

What are some of the traditional methods used to combat the effects of heat stress on turfgrass?
Golf course superintendents have long battled the ill effects of sun and heat stress by using an array of methods. The include things such as raising the height of cut, reducing mowing frequency, rolling instead of mowing, switching to solid front rollers on greens mowers, avoiding mowing wet greens, regular applications of soluble nitrogen and fungicides, periodic venting to improve root zone gas exchange, and irrigating and syringing the turf as accurately as possible.

Now, superintendents have another tool for their turf-care toolbox: Turf Screen!

What environmental factors besides sunlight determine heat stress levels?
Heat related injury and the associated decline in turf quality is often a result of a complex of individual factors acting together. For this reason it is often difficult to pinpoint the specific causes of summer decline. Besides air and soil temperatures, another extremely important environmental influence on the plant’s ability to cool itself through transpiration is the relative humidity. At high relative humidity the plant is much less able to effectively cool itself and as a result is even more prone to heat buildup and direct heat injury. Wind speed and tree shading can also be important.

In summary, the following environmental factors determine the relative level of heat stress your turfgrass will be subjected to:

  • Air temperature
  • Soil temperature
  • Relative humidity
  • Wind speed
  • Tree shading
  • Radiation intensity

High soil temperature can be more detrimental than high air temperature because root growth is harmed when soil temperature is too high. Several studies have demonstrated that reducing root-zone temperature helps maintain quality creeping bentgrass under high ambient temperatures.

The beauty of Turf Screen is that by reflecting harmful ultraviolet and infrared light it not only protects turfgrass leaves but lowers the soil temperature, too, thereby promoting a stronger, more resilient root system.

What happens to turfgrass when it is stressed by heat?
The leaves of a plant have small openings called stomates, which are its breathing holes. Mostly they let carbon dioxide in and oxygen out, as well as allowing water to be ‘transpired’. The plant can control the loss of water from its leaves (i.e., transpiration) by varying the aperture of its stomates (like a tap). Transpiration is important because it keeps the stomates open so that exchange of gases can take place during the photosynthetic process. When excessive heat causes a plant’s stoma to close, its ability to photosynthesize is impaired.

When a plant restricts the flow of water vapor out of its leaf it automatically restricts the flow of CO2 into the leaf for photosynthesis. This is known as the transpiration compromise or the plant version of “there are no free lunches.”

The roots of turfgrass are also adversely impacted by heat stress. The optimum temperature for root growth of cool-season grasses ranges from 50°F to 65°F. New root initiation ceases at a soil temperature of 80°F. Soil temperatures above 86°F will cause root growth to stop and roots to begin to lose their ability to function, and the natural aging process of the existing root system begins.

Sunlight and photosynthesis
Sunlight reaching your golf course’s turf is composed of:

  • 4% ultraviolet (UV) light
  • 52% infrared (IR) or weaker light
  • 44% visible light

Plants only use visible light in the process of photosynthesis because:

  • IR light does not contain enough energy for photosynthesis.
  • UV on the other hand has too much energy, and in a sense can’t be controlled by plants. UV light intercepted by plants (and us) can create free radicals, which can break chemical bonds in an organism. This is detrimental to the plant. Plants in fact have pigments to protect them from UV light.
  • Visible light, however, seem to be just right for plants to use to move electrons around.

As photosynthesis occurs, the wavelength spectrum that is most beneficial to plant growth is found within certain areas between the 380-720 nanometer range of the spectrum (see following chart). The light that is within this region is referred to as Photosynthetically Active Radiation (PAR).

Chlorophyll Absorbtion Chart

Nanometers PAR Influences
200 – 280 UVC ultraviolet range; extremely toxic to plants.
280 – 315 UVB ultraviolet light; causes plants colors to fade.
315 – 380 UVA ultraviolet light; is neither harmful nor beneficial to plant growth.
380 – 400 Start of visible light spectrum. Chlorophyll Absorption begins. UV protected plastics ideally block out any light below this range.
400 – 520 This range includes violet, blue, and green bands. Peak chlorophyll absorption influences photosynthesis. Most significant in promoting vegetative growth.
520 – 610 This range includes the green, yellow, and orange bands and has little absorption by receptors.
610 – 720 This is the Red band where large instances of chlorophyll absorption occur which promote flowering and budding.
720 – 1000 There is little chlorophyll absorption in this range. Flowering and germination are influenced at the high Far-Red end as infrared heat.
1000+ Totally infrared range. All energy absorbed at this point is converted to heat.

What is the sunburn mechanism in a plant’s cell?

Sunburn is triggered by direct DNA damage. When the cells’ DNA is damaged by UV radiation, type I cell-death is triggered. The damage is recognized by the plant, which then triggers several defense mechanisms, including DNA repair to revert the damage. While proper repair occurs in the majority of DNA damage, the plant’s repair mechanisms cannot keep pace during extreme exposure to UV radiation, resulting in sunburn, plant tissue damage and reduced photosynthesis.

Climate Change
Many golf course superintendents say they suspect the last few years of dramatically hot summers are a portent of things to come due to climate change. Turf Screen was invented by a golf course superintendent who was searching for ways to better deal with heat stress impacts on his course, which seemed to be getting worse each year.

Of course, more than hotter summers are predicted. Other impacts associated with climate change include:

  • More weather extremes
  • Less predictable Weather
  • More intense storms (increased damage)
  • Greater frequency of floods
  • Rising sea level (loss of land and golf holes)
  • Increased demand for irrigation

We located the following guride on how superintendents can plan for climate change. Golf was developed in Scotland, where the art of greenkeeping was born, so it seems appropriate that this visionary report emanates from there. Although some of the information is specific to Scotland and the UK there are certainly many ideas that US superintendents will find useful. http://www.sgeg.org.uk/SGEpdfs/Climate%20Change%20and%20Scottish%20Golf%20Courses%20%28SGEG%202004%29.pdf

A PowerPoint presentation on how climate change impacts on US golf courses made to the American Society of Golf Course Architects can be found at http://www.agrowinginterest.com/presentations/Marzolf_Tom.pdf.

WeatherBill Inc. published a 2007 study analyzing historical weather data to determine changes and trends in annual Golf Playable Days. The study concludes that U.S. golf playable days are increasing in 95 cities, primarily due to higher average temperatures. The study also identifies increasingly rainy trends in the Northeast and Southeast, a drier Southwest and West, and increasingly uncertain weather in 33 cities. The free study can be downloaded at http://www.weatherbill.com/assets/LandingPageDocs/golfstudy.pdf.

Is “scald” the same as sunburn?
Scald occurs when turfgrass is submerged in standing water after heavy rainfall. When the sun emerges in conjunction with high temperatures, the turfgrass is “cooked,” for lack of a better term. Turfgrass can survive standing water for longer periods of time when temperatures are cool. High temperatures and standing water lead to rapid turfgrass decline.

Air vs. turf canopy temperature
An important point to remember in measuring heat stress is that standard meteorological weather data records temperature at 5 ft. above the ground and that temperatures at the turf level may exceed the recorded high. At a Middle Atlantic course, for instance, when air temperatures were 93 degrees F, the actual temperature at the surface canopy of a bentgrass/Poa putting green was 106 degrees F.

Of course, high air temperatures are only part of the cause of reduced plant vigor. High soil temperature can adversely impact root growth and thus overall turf quality.