Joseph W. Rimelspach
John R. Street
Karl Danneberger
William E. Pound
Barbara Bloetscher
Joseph W. Rimelspach, Ohio State University Extension/Department of Plant Pathology; John R. Street, Ohio State University Extension/Ohio Agricultural Research and Development Center; Karl Danneberger, Ohio Agricultural Research and Development Center/Horticulture and Crop Science; William Pound, Ohio State University Extension/Horticulture and Crop Science; and Barbara Bloetscher, Ohio State University/Horticulture and Crop Science
The 1995 growing season was a difficult turfgrass maintenance season for golf course superintendents and other turfgrass managers throughout the Midwest. The Ohio State University Plant and Pest Diagnostic Clinic received numerous turf samples from Ohio and surrounding areas. Ohio State faculty and staff received more telephone calls and requests for on-site visits than any other summer in recent history. A major factor influencing turfgrass health on golf courses this year was the extreme environmental conditions. There is nothing more frustrating for golf course superintendents or turfgrass managers than to have to deal with adverse weather that is out of their control. This year presented some dramatic abnormal weather patterns that had tremendous impact on turfgrass growth and performance.
The environment during the spring and summer of 1995 was very conducive to extreme plant stress, turfgrass diseases, and turfgrass decline. It was one of the worst summers on record for growing high quality turf under the intense management of the golf course.
It is important to realize that the types of grasses used on golf courses in all of Ohio and the Midwest are cool-season grasses. Cool-season grasses, as the name implies, grow and prosper best under cool moist conditions of spring and fall. Shoots and leaves (tops) grow best at temperatures of 60-750 F. Roots of cool-season grasses grow best at soil temperatures of 55-65 degrees F. Air and soil temperatures this summer far exceeded these ideal ranges for extended periods of time.
Turfgrass types in the cool-season group include creeping bentgrass, Kentucky bluegrass, ryegrass, fescue, and annual bluegrass (Poa annua). These turfgrasses develop a dense, healthy plant community with a deep prolific root system in the cool periods of the year. The latter development is imperative for turfgrasses to form resistance to environmental and cultural stresses and disease pathogens that are encountered in summer.
The spring of 1995 was cool but wet in most of the state. Rainfall records were set in many areas. Although the shoots and leaves (tops) of the turf looked green and lush, and playability was good to excellent, the turfgrass root system was actually declining, with wet saturated soils resulting in short roots with a significant loss of root mass. Root systems on golf courses with good drainage and well-built greens developed better than on poorly drained greens.
Perhaps the most devastating environmental blow was the summer heat and humidity. Summer conditions did vary somewhat throughout the state, but in general temperatures were very hot and humidity was consistently high.
For much of July and August, daytime temperatures were 90 degrees F or higher, and nighttime temperatures were 700 F or higher. Nighttime temperatures on many nights remained in the high 80s until midnight or later. Particularly unusual and oppressive this summer was the number of consecutive days of high daytime and nighttime temperatures. In many cases, these high temperatures lasted more than six weeks.
Normally, hot periods in the summer are interspersed with cold fronts that bring several days of cool weather to assist in turf recovery. These intermittent periods of cool weather coupled with usually cooler nights throughout the summer are critical to the overall health and survival of cool-season turfgrasses. Hot humid days and nights provided no relief for turfgrasses in July and August.
High temperatures placed an extreme physiological stress on cool-season turfgrasses. First, photosynthesis (food production) slows as temperatures increase into the high 80s and 90s and is drastically reduced as temperatures approach 100 degrees F. Respiration (utilization of food reserves) increases as temperatures increase.
High day and night temperatures in July and August resulted in high rates of respiration. As a result of low photosynthesis and high respiration, available food in the turfgrass plant was depleted. Under this scenario, day by day the turfgrass plant continued to weaken.
Annual bluegrass (Poa annua) was the cool-season grass most affected by these extreme weather conditions. It is considered to be the least tolerant of the cool-season grasses to heat and stress. Golf courses with high populations of annual bluegrass had extensive damage.
Soil temperatures at the 1- to 2-inch soil depth (i.e., where most of the roots existed this summer) were often only a few degrees lower than air temperatures. Temperatures in the turfgrass canopy were usually higher than air temperatures. At midday, soil temperatures were often measured at 100 degrees F or above, especially on sand greens.
Optimum soil temperatures for root growth of cool-season grasses are 55-65 degrees F. It is not surprising that turfgrass roots began to die back. Bentgrass will not initiate new roots when soil temperatures exceed 90 degrees F. High soil temperatures resulted in root decline and no opportunity for root regrowth and recovery.
Turfgrass plants with deteriorating root systems became extremely susceptible to disease and stress. Weakened plants recovered poorly even where excellent fungicide programs were being used.
Excessive soil moisture occurred throughout many parts of the state. With heavy rainfall, oxygen level was reduced in the soil, suffocating roots. Waterlogged soil coupled with high temperatures caused rapid and extensive root dieback and death. In many cases, superintendents can pinpoint a specific day or time period that was the breaking point for turfgrass on their course.
Wet conditions also promoted algal growth on the soil surface that spread to leaf surfaces. This contributed to turf thinning and decline. Algae that formed on the soil surface were difficult to break up, and further slowed soil drying.
In late August, daytime temperatures remained high, relative humidity decreased, and winds increased causing extensive evaporation of water from turfgrasses. With a very shallow root system, the turfgrass plant rapidly lost water, wilted, and declined.
Due to these weather patterns, turf roots on many greens and fairways became short and stunted resulting in a fragile plant system. This turf continued to thin despite cultural and chemical attempts to revive it.
Upon evaluating golf courses throughout the state, the amount of play was directly correlated with success or failure. Golf courses with high use (i.e., especially public golf courses) had more turf loss. Many courses only suspended play during the time of actual thunderstorm or rain shower activity. If play was resumed shortly after rain under wet conditions, extensive damage occurred. Play on heat stressed or wilted turf also caused damage.
Turf was also damaged where golf carts and maintenance equipment were repeatedly driven. If the soils were wet, compaction and turf injury increased. In situations where the turf and soil were dry, the crowns were often injured. Tire tracks led to unusual symptom patterns and extensive damage to turf, especially in fairways.
Some golf courses have tournaments or special events at various times throughout the year. To prepare for these, greens were often cut lower and more frequently to increase ball speed. If these maintenance practices were performed during the hot stress period, the already fragile turf was seriously weakened. In a number of instances, these events occurred around the fourth of July; and for the next two months, turf had no opportunity to recover. These golf courses struggled with serious problems throughout the rest of the summer.
Green size was another factor influencing success or failure. In general, courses that had larger greens, where pin placements were spaced out and wear was distributed over a larger area, survived much better than smaller greens.
Most golf course superintendents respond to the golfer's desire for faster greens. This is often accomplished by lower mowing heights, more frequent mowing, rolling, frequent topdressing, and related activities. All these factors place additional stress on the turfgrass plant. In most years these practices can be performed and turf maintained. There was little opportunity this year for turf recovery. If anything further weakened the turf, it declined or developed serious problems.
In most instances where golf courses maintained high quality turf throughout this summer, some significant alterations were made in mowing practices. First, mower height was raised early before the onset of heat. Second, grooming rollers were replaced with smooth rollers on greens mowers. Again, these practices were instituted before adverse weather and disease weakened the turf. Third, superintendents switched from riding greens mowers to walk behind greens mowers. Complaints were received by superintendents about slower greens; however, turf was maintained more successfully throughout much of the summer.
It must be pointed out that mowing height plays a dominant role in the health and vigor of turfgrasses. Allowing more leaf area to remain results in more food produced for the plant. In fact, only a small increase in mowing height (i.e., 1/16 to 1/32 inch) can have a significant impact on reducing turf stress. Also, slightly higher mowing heights will increase rooting depth and mass. Greens speed may have to be sacrificed for the overall betterment of turf and playability under extreme environmental conditions.
The first element of water management is proper drainage. Proper drainage includes both surface and internal soil drainage. Golf courses with low areas on greens or fairways had much more damage than courses that were designed with good surface drainage. Courses that had inadequate soil drainage had serious problems managing water and disease problems.
The second element of water management is irrigation system design and management. Many golf courses showed inadequacies in the present irrigation system either due to poor design or operation problems. As a result, certain areas of the course were too wet while others were too dry.
Syringing is a practice of supplying light amounts of water to turf. This is used to prevent wilt of turf during hot and dry periods and to cool turf under hot conditions. In Ohio, depending on the summer, syringing may be used occasionally to quite frequently. This year, syringing had to be used extensively to cool turf.
The challenge in many cases is to syringe turf with saturated soil without adding to the existing moisture problem. There was little option but to apply water to cool the turf and keep it alive.
Managing turfgrasses in the summer of 1995 was a complex and challenging job. Many different factors interacted to cause turfgrass decline and failure on golf courses.
Weather played a dominant role. In short, excessive rainfall, oppressive day and night temperatures, and humidity gradually produced weakened turfgrass plants. These plants become vulnerable to disease and environmental/cultural stresses causing turf decline.
Turfgrass plants became so weak that they lacked enough vigor to respond to even the best programmed pesticide and fertilizer applications by golf course superintendents.
Managing fragile grass during a summer as severe as 1995 demands a reduction in cultural stresses, a thorough knowledge of turfgrass science, and cooperation between the superintendent, golf club owners, and members. The 1995 season presented an opportunity to learn and plan for the future.