At this time of year, many courses experience localized dry spots (LDS) on sand-based putting greens as day length, temperatures and evaporative demand increase. Rainfall also dissipates in western states as we move closer to summer. LDS shows up as a camouflage pattern and occurs most frequently on sand-based putting greens with little organic matter, but it is also commonly seen on mounds and south-facing slopes.
The pattern very much resembles its name; it looks like a bunch of localized dry spots. These small, irregularly shaped patches form due to excessively dry conditions. Looking at soil cores or using a soil moisture meter quickly reveals dry sand or soil that often is so dry it is dust-like and will not stick together. If left unmanaged, the dry conditions will result in significant turf decline, especially with cool-season grasses.
Observation and treatment of LDS is nothing new to golf course superintendents. Many, if not all, use some type of wetting agent on the localized patches, but wetting agents don’t guarantee remediation. A 1-inch rain event will often do the trick, but in the absence of rainfall superintendents must replicate this deep watering with irrigation. They should continue to use wetting agents, but occasional deep irrigation events are also a crucial part of properly wetting the entire soil profile.
Applying irrigation every night at light rates most certainly will not improve LDS. It is recommended to apply a minimum of 1 inch of water during an evening irrigation cycle to thoroughly wet the soil profile. To do this, set a shorter run time of 5-10 minutes per sprinkler followed by a minimum of 20 minutes soak time, and repeat until the run times on each sprinkler yield 1 inch of water. Run the sprinklers individually and preferably on opposite sides of the green, not one after another in close proximity, to avoid creating runoff or puddling. On larger greens, two sprinklers can run at one time as long as the throw lengths are not close to one another. If you aren’t sure how much water a green can take before runoff occurs, conduct a daytime test at an opportune time.
The total water window may be 8-10 hours in some cases depending on the run time, number of sprinklers per green and the necessary soak time. Be patient with the process, there is no point in applying this water to have it sheet off the green and soak the surrounds. This process works best with part-circle sprinklers with individual head control but can be deployed with full-circle sprinklers.
It is best to use the irrigation control software to calculate the run times necessary to apply a minimum of 1 inch of water based on each sprinkler arc. If this process sounds uncomfortable, try it on one green multiple times and space the deep soaks at least one week apart, then observe the results. Most will see the process mitigate LDS and significantly reduce the reliance on hand watering much more effectively than a frequent but light irrigation approach. Those lucky employees pulling hoses will thank you! If you would like to learn more about deep irrigation and want to improve your surface organic matter management program, please reach out to your regional USGA agronomist.
West Region Agronomists:
Brian Whitlark, regional director, West Region – bwhitlark@usga.org
Ross Niewola, agronomist - rniewola@usga.org