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Heat Straining Golf Courses

By David Shefter, USGA

| Aug 3, 2010

As long as the weather extremes continue, USGA Green Section agronomists consider it necessary and appropriate to practice defensive maintenance and management.

The summer of 2010 is on a pace to break temperature records up and down the East Coast and along the Gulf of Mexico. For example, Washington, D.C. had 40 days of 90-plus-degree temperatures in June and July, more than typically occur in an entire average year (37). During the recent U.S. Girls’ Junior Championship at The Country Club of North Carolina in the Village of Pinehurst, the heat index reached triple digits, topping out at 110.

Needless to say, this has put tremendous strain on golf courses and those in charge of maintaining them.   

USGA Green Section agronomists consider it necessary and appropriate to practice defensive maintenance and management programs as long as these weather extremes continue. Obviously, extra care must be taken to pamper the grass through this difficult weather, and understanding from golfers is also a must to help get through the crisis. If everyone works together and does what is best for the grass, the summer of 2010 will one day be nothing more than just a bad memory.   

By way of letters sent to USGA Member courses and via communication through the Green Section Record, the goal has been to alert golfers and turf managers alike about the extraordinary weather conditions and turf-loss-related matters. This extended period of heat and drought – followed by heat, humidity and thunderstorms – has caused and probably will continue to cause turf stress and turf loss throughout the affected areas of the country. 

“No two golf courses are alike, having different grasses, soils, course features and golfer expectations,” said Stanley Zontek, director of the Mid-Atlantic Region for the USGA Green Section. “It is important that golf course superintendents use defensive golf course maintenance programs. That is, be conservative and pamper the grass. The turfgrass is under intense weather stress, which is compounded by an increase in disease pressure. Everyone should be more concerned about plant health than green speed.

“There is an old adage in our industry: Slow grass is better than no grass. This is not a joke. It needs to be taken seriously.” 

Some suggested management programs include: 

Maintain a solid fungicide program: With heat, humidity and thunderstorms, fungicides do not last as long and disease pressure is greater. There is no better money spent than in protecting the grass from disease. If the fungicide budget is being depleted, pull back in other areas. However, when conditions are this difficult, fungicides often cannot completely overcome disease incidence. It may well be a case of reducing disease injury rather than eliminating it altogether. The following steps are just as important as applying a good fungicide.

Raise mowing heights and use sharp mowers: This can help the grass survive.

In an age of rising expectations for putting-green performance, the recommendation to raise the mowing height on bentgrass greens to promote better summer survival is not a popular one for golfers. Of course, failed putting greens in late August are not popular, either. However, science is on the superintendent’s side on this one. 

The benefit of raising the mowing height in the summer can be explained by looking at the relationship between energy production (photosynthesis) and energy consumption (respiration) in the summer. As temperatures increase, the rate of photosynthesis in cool-season grasses (bentgrass) decreases, but the rate of respiration increases.  Explained another way, energy production is slowing while energy consumption is increasing. This is not sustainable over the long term because, eventually, the plant is going to run out of fuel. 

Chris Hartwiger, a USGA Green Section senior agronomist based in the Southeast Region, says that raising the mowing height increases the amount of leaf surface area, which increases the amount of potential photosynthesis. In essence, the higher mowing height is creating a bigger tank of fuel for the plant, and hopefully, the fuel will not run out until cooler temperatures return in the fall.

Mow less…roll more: The goal is to reduce mechanical stress to the grass plant. Mowing is a stressful practice for bentgrass putting greens in the summer months. Researchers at the University of Arkansas found that, by mowing three days per week and rolling three times per week, green speeds would remain consistent throughout the week.   In the field, we have observed this practice used in the summer months, and superintendents report favorable results with respect to turf quality. Therefore, if stress is high, reducing mowing frequency and substituting rolling is an option to consider for limiting stress. 

Switching from grooved rollers to solid rollers will also protect collars from the turning of mowers.

Carefully monitor course traffic: Traffic causes additional stress when grasses are already weakened by high temperatures. During these difficult economic times, every golf course wants as much play as possible, but traffic patterns need to be managed carefully. “During these stress periods, we emphasize the importance of using ropes and stakes to manage traffic flow on and off greens. In some cases, weak putting greens may need to be closed,” said Bud White, director of the Mid-Continent Region.

Spoonfeed the grass: Bob Brame, director of the North-Central Region, emphasizes the importance of staying consistent with a light and frequent foliar feeling. Excessive grass growth depletes carbohydrates (plant food). Iron (to keep the grass green) and growth regulator applications will be part of this mix. 

Air movement: On shaded or pocketed greens, prune tree limbs, use fans, and generally keep the air moving.  When you are hot, you stand in front of a fan to cool yourself. When the grass is stressed, it needs good air movement as well. Drier turf is also less prone to disease.

“Fans have proven in research trials and in the field to be a valuable bentgrass life support tool,” said Hartwiger. “Fans should be running 24 hours a day right now. If portable fans are available, use them and rotate them throughout the property as needs dictate.” 

Do not over-water: Manage water applications carefully, and hand-water if possible. Lightly syringe the turf with the nozzle. If you are wetting the soil, it’s too much. Any midday watering should be focused on cooling the turf canopy. Remember, you can always add more water, but wet, saturated soil can damage newsContents, increase disease and contribute to turf loss via wet wilt. If corrective watering needs to be done to curtail dry spots, the extra water should be applied in the early morning or late in the evening. Do not over-water the grass in midday heat. 

Watch the putting greens carefully and add supplemental water as often as needed to prevent shallow-newsContented bentgrass from wilting. 

Surface aerate the greens: This allows the soil to breath, excess moisture to escape, and newsContents to regrow, thereby helping the grass to survive. 

Venting the putting greens is another way to properly maintain turf. Venting is a term that applies to the practice of creating small, non-disruptive holes in a putting green for the purpose of improving gas exchange, increasing water infiltration, and stimulating new newsContent initiation. The term venting is used instead of aeration because of the negative connotations golfers associate with the term aeration. Venting is a golfer-friendly practice. 

Dr. Robert Carrow, of the University of Georgia, found that the ideal venting frequency in his research plots was every 21 days throughout the summer months. For the summer of 2010, the Green Section recommends venting greens every two to three weeks until fall core aeration arrives.

None of these suggestions by themselves will make the difference between putting green survival and serious injury. It is important to implement all of these suggestions to the greatest degree possible. Although you can’t do much to control the weather, these are steps that will help in the long run.

Green Section agronomists will continue to do everything possible to help courses through this difficult year. For additional information and weekly updates, subscribe, at no charge, to the Green Section Record at: