In most years, August 15th is looked upon as the “whew!” date to get past for managing bentgrass putting greens in Missouri. Not in 2014. A sustained blast of late August/early September high temperatures plus precipitation led to a number of problems on creeping bentgrass putting greens over the last three weeks. The first weather wallop occurred over the Labor Day holiday when 2 to well over 5” of precipitation occurred in a 24-hour period over much of the I-70 corridor. This left hook broke a single day rainfall record in Columbia, and amounted to the Kansas City region being 1-2” and the St. Louis area being an outstanding 4”+ above normal during the previous 14 day span. This first punch of saturation landed on putting greens that had accumulated a (mild) summer’s worth of organic matter, which held onto it like a sponge. The right uppercut occurred two days later, when temperatures soared into the mid-90’s with high humidity on a root system and soil profile that was still soaked. To add insult, a final 0.5 – 1” of rainfall fell on September 5th in some areas, just to make sure the root system stayed wet.
Despite the summer being fairly mild from June – early August, late August and early September turned flat out ugly in Missouri for superintendents managing golf putting greens. The Plant Diagnostic Clinic has received an unprecedented number of putting green samples over the past three weeks, and abiotic causes of decline top the list for turfgrass decline (detailed in the main section below). On the bright side, the current forecast shows a marked decline in temperatures and a drier than normal rainfall pattern over the next 6-14 days. For renovation, some supplemental irrigation over the next 10-14 days may be required to keep seed wet, but for turfgrass roots with extremely soggy feet the dry down will be welcome.
The aforementioned problems relating to Pythium root rot, patch diseases, surface algae, and black layer on bentgrass putting greens were all a product of the overall predisposing factor of a wet root zone combined with high temperatures. As detailed above, these two environmental factors occurred in spades from Sept. 1 – 5, but occurred in more minor local events in middle – late August. These conditions caused physiological root decline in response to the high soil temperature and low gas exchange caused by the saturated system.
Another factor in this decline may be the timing of our heat stress event in 2014. By previous summer standards, June and July had much less temperature stress than in normal summer months. Managers may have reduced inputs on golf greens, perhaps skipping a venting application or two, or skipping a watered-in fungicide application. Meanwhile, the bentgrass is growing well, and therefore the organic matter in the soil is still building. The soil microbial community may not have been working at full capacity due to the reduced temperatures, or a skipped venting didn’t allow enough oxygen to these microbes or the roots. All of a sudden the shock of a high rainfall event causes this excess organic matter to saturate and hold water. Roots in this saturated layer lost access to oxygen and a subsequent 48-72 hours of sustained + 90 degree temperatures initiated the rapid decline. Pathogens and competitors were happy to oblige the roots in their demise.
Dr. Peter Dernoeden detailed this wet wilt situation in a great publication the March/April 2006 USGA Green Section Record (click here to read this great article again). With the compromised root system and high night temperatures, bentgrass had little chance in relieving themselves through the cooling process of transpiration, and in a sense boiled over the 3-week span. In some instances, the greens became puffy after a rainfall event and scalping may have further reduced the plant’s transpirational ability.
Several practices aimed at stress reduction are recommended during a wet wilt or high temperature, saturated soil condition. A change in mowing practices, especially raising mowing heights, alternating mowing and rolling, and switching to smooth rollers, is often necessary during these late season stress events. Venting or spiking greens before and after a considerable rain event may help dry out the upper 2” of the soil profile and reduce the amount of black layer, algae and root loss that occurs due to inadequate gas exchange. Lastly, most of the current samples came from greens that are perennial problems due to lack of air movement. As is normally the case, none of the current samples came from a green with a fan, demonstrating how critical air movement is in cooling the turfgrass canopy, removing water from the system, and reducing soil temperatures.
Now that we are back in the gravy for cool-season root growth, and it appears we are going to stay there, fertilization and recovery should ensue. If afflicted, a dry down aided by an aerification event, followed by a watered-in fungicide to stop the secondary pathogens and a good push of fertilizer should aid recovery,. As many have looked forward to through this past tough month, it’s time to hear the sweet whine of the working tine.
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Extension Turfgrass Pathologist
University of Missouri