Features Agronomy
Like it or not, it’s time to think ahead to the heat of summer

By Sean R. Jordan, T.Ag.
Agronomist

IN the last issue, I wrote about a fictional movie on a golf course
called “A Beautiful Spring.” If this current issue’s article were a
movie it, in true Hollywood fashion, would be about a highly overrated,
and ultimately less enjoyable, sequel called “A Hot Summer.”

Just at the mention of summer, many superintendents go into a cold sweat, thinking all of the things that could happen to the turf they manage: disease, insect pest infestation, wilt, drought, traffic and so on. All of these things are inevitable, especially since the turf that we are forced to grow in this climate suffers the most environmental stress when in highest demand. No turf manager wants to see or, even worse, make excuses for thin, patchy or blighted turf at the peak of the season. Ultimately, keeping turf happy and healthy requires turf managers to maintain a cool head on their shoulders even in the greatest heat.

As the temperature rises and the plants start using the water taken up from the soil for cooling as well as normal metabolic functions, turf has to reallocate some of its efforts. During this time, the photosynthates produced by the leaves fall below the level required for survival, causing the plant to start taking energy from the carbohydrate reserves built up during the spring and previous fall. Simply put, more energy is being spent on growth than can be made by the leaves. Keeping this in mind will help answer the question of “Where did my roots go?” in mid to late-summer. 

Other factors such as a spring-active root diseases and root-feeding insects may weigh in on the question of what is happening in the soil during the summer season. Having a handle on the quality and quantity of root mass in the turf system is crucial when deciding how to feed and provide water. Relying on a weak root system to take up water and nutrients can leave the turf lacking the ability to fend off biological attackers (disease and insect pests) and recover from abiotic stressors (wear and damage).

Maintaining a consistent supply of available nutrients without causing surges in growth is a balancing act necessary for the turf to repair itself from the wear of daily play without taking away from the already reduced carbohydrate reserves. It may become necessary to incorporate foliar feeding into the fertility program for a period ranging from a few weeks to several months if the roots simply cannot intercept or take up enough nutrients. Use of the many different slowly-available nitrogen fertilizers is essential to maintaining steady growth with fewer surges that could reduce the turf’s reserves and increase disease susceptibility.

Irrigation regimes during these types of periods would also need to be adjusted to accommodate the “less-than-average” state of the root zone. Although the strategy of deep and infrequent watering to encourage root growth has been preached as turf gospel for decades, consideration must be given to the fact that roots may not grow and, in fact, can be reduced during summer months. Due to variations in root zones, microclimates and even topography of turf may make it necessary to manage more individually the different areas of the course. 

Using the deep and infrequent method of irrigation may necessitate syringing, or placing a thin layer on the surface of the turf to absorb heat and cool the canopy without supplying water to the soil. This is a well proven method but can easily be performed incorrectly if the person on the end of the hose becomes a bit overzealous with the water. If too much water is applied to a hot soil, it could cause scorching of the roots which would set the turf back even further in a time of real need.

As mentioned earlier, turf managers are unavoidably “behind the eight ball” as play peaks during the hot months of summer, and yet the turf is expected to be in top shape. The expectations for ball-roll distance and consistency, on greens especially, create a nightmare scenario for managers that force them to sometimes push turf beyond its limits. Lowering the height of cut is typically the first route many take to increase these measures of a green’s “quality.” 

Research was recently performed at Rutgers University to measure factors contributing to anthracnose incidence and severity. In this study, the researchers looked to alternatives to lowering cutting height while still maintaining acceptable ball roll distance. Initial results indicate that greens height of annual bluegrass turf double-cut daily to 0.141 inches achieved similar ball roll distance as cutting once-daily to 0.110 inches. 

A study at the Virginia Polytechnic Institute showed similar results on creeping bentgrass in that the turf cut to 0.140 inches and rolled two to three times per week still had a slightly lower ball roll distance and maintained greater health throughout the hot and humid months of summer than that cut to 0.120 inches.

Disease prevention is a primary focus of the practices performed in summer to reduce stress on turf. Consistent with the idea of disease incidence reduction, a plan to remove dew and guttation fluid in the morning can play a major role. A layer of dew helps to maintain a favourable environment for disease development, and the amino acid and sugar-rich guttation fluid from inside the turf plants provides a little nourishment for the growing fungi. While many balk at the idea of dragging the dew from fairways, simply taking the time to calculate the man-hours to remove dew in the morning can show that the reduction in chemical treatments will pay for the labour. This practice can also help the subjective judgment of the fairways in that golfers will be playing on dryer turf sooner and mowers will be less likely to leave excess clippings caused by the moisture.

Throughout this discussion there have been many ideas about reducing the summer heat stress and ultimately disease incidence that should make our turf more able to defend against the stresses of the season. Much to the same idea that I used in the last story, planning is crucial to survival. It is necessary to consider all of the factors that contribute to the health and well being of the turf, from height of cut and irrigation scheduling to nutrition and even processes as simple as dew removal.