Heat Taking a Toll on Golf Turf

Heat taking a toll on golf turf
July 21, 2012

Though golf turf is still performing fairly well in spite of heat and drought, cool-season turfgrasses simply cannot survive the extended heat. As one local superintendent quoted, ”Temperatures like this is why they grow zoysia just an hour or two south of here.” The reason cool-season grasses cannot survive extended heat is physiological. Cool-season grasses reach maximum photosynthesis near 75F air temperature and drop off sharply at higher temperatures. Conversely, respiration or energy consumption of cool season grasses increases with rising temperatures. At elevated temperatures, cool-season plants are in energy deficit where they are using more energy in respiration to stay alive than they are producing in photosynthesis. All grasses can survive this energy imbalance for a given period by using carbohydrate storage accumulated earlier in the year when photosynthesis
was higher than respiration.

How long they will survive this energy imbalance is complex and depends on many issues such as duration of elevated temperatures, frequency of cool nights, species, cultivar, previous maintenance, mowing height, traffic, etc. Often when these plants are weakened, it takes one small stress to put the plant over the edge or the proverbial straw that breaks the camel’s back. Small stresses include slight drought stress, minor disease, traffic, a light dusting of topdressing, insect feeding, etc. The bright spot this year for golf courses is the drought and relatively low humidity has limited most of the damaging diseases and allowed superintendents to manage irrigation to keep turf dry. Annual bluegrass is the weakest turf species during the summer, and is always the first to die. Annual bluegrass on golf courses is currently yellowing and I’d expect it to start to thin and die in the very near future given the current forecast of the next four days above 100F in eastern NE. Fungicides and previous applications of trinexapac may help delay the decline, but it is difficult to avoid the inevitable thinning of annual bluegrass in a year like this. Perennial ryegrass on tees and fairways can also be one of the weaker species, and weakening from the heat is often exaggerated by pythium, brown patch, or potentially gray leaf spot. Fungicides may be effective at preventing widespread damage on perennial ryegrass.

As mentioned in a previous Turf iNfo (http://turf.unl.edu/pdfctarticles/juneheat.pdf), following are practices to minimize stress on golf turf:

• Continue to manage irrigation to keep turf as dry as possible while staying away from drought stress. This will maximize soil oxygen to maintain roots, while also providing ample soil water so the plant can cool itself.
• Syringe annual bluegrass in middle of the day. This works on turf with compromised root systems (annual bluegrass, seedlings of other grasses, or turf affected by white grubs or summer patch.
• Continue preventative fungicides to minimize additional stress.
• Roll greens whenever practical to maintain speed instead of mowing. Continue mowing as needed, but be sure turf is well-watered to insure no extra damage.
• The drought will concentrate egg-laying of masked chafers and/or Japanese beetles to irrigated turf areas.
• Watch for breaks in your insecticide applications.
• Switch to solid rollers instead of grooved rollers on all reel-type mowers.
• Aerify as needed with solid narrow tines to increase water and air movement. Insure the areas are wellwatered prior and consider this during cloud cover or in the cooler parts of the day.

Zac Reicher, Professor of Turfgrass Science, zreicher2@unl.edu, turf.unl.edu