Early Spike Set to Cool Down
What a summer it was! Okay technically summer isn’t over if you’re an astronomist. However, most would rather the meteorological definition of September 1 signifying the beginning of fall since both us and the grass could use some recovery. June had all the hallmarks of starting a drought akin to 2012, then flipped completely into a washout. July – August 2016 will fall in the top 5 wettest that Missouri has experienced. Along with the rainfall, intense humidity, similar to 2010 and 2011, plagued the region.
The Historical Highs (or Lows) of Summer 2016
Stagnant Gulf of Mexico air masses, combined with the added humidity from evapotranspiration, resulted in a brutal mix of humid, and constantly warm air. The average 2016 summer dew point temperature for Missouri is in the top 4 since records were kept in 1920. This humid air did a few things. Along with us, the humidity made plants, particularly short ones on putting greens, very uncomfortable. Plants need to perspire, or transpire, in order to keep cool, and all that excess water vapor already present in the air slows this evaporation process. Wet wilt was a common occurrence, as grasses couldn’t take up or get rid of the amount of water needed to cool themselves off (see this previous update for info on this condition). Second, the humidity put a damper on the daily high temperature, which was about average in 2016, but held the heat like a plastic bag at night. The average low temperature in June - August 2016 was 67.2 F, 3.1 degrees above average and the 4th highest on record tied with 1954. Since water that gets hot tends to stay hot, soil temperatures averaged 90 degrees on many days. A historically bad summer for cool season turfgrass, specifically bentgrass and low mowed tall fescue/Kentucky bluegrass sports fields or lawns.
The forecast does offer a welcome glimpse of fall temperatures and fall recovery. Temperatures are expected to be mild in the middle part of September, along with some healthy chances for participation. Remember one of the main advantages of cool season turfgrasses is they can be seeded and for the most part quickly established compared to warm season species… so do it.
Fall Expected for mid September
Gray Leaf Spot on Tall Fescue
Basal Rot Anthracnose
Drainage Check May Be Necessary on Putting Greens
Many, many putting green samples have been submitted for diagnosis this year, and most have had one thing in common – a saturated root zone. As stated above, the environmental conditions had quite a bit to do with this, since hot, humid conditions didn’t allow bentgrass roots to effectively take up the water and dispel it, while the clouds were often very good at overdispensing H20. Organic matter accumulation from retreating roots and stolons compounded the problem by holding onto water. The common recommendation is to tine, tine, tine… to release potentially hot, suffocating water out of the saturated soil profile and provide a less hospitable environment for pathogens.
In some of these cases, however, perhaps the submitted samples can’t tell the whole story. The depth of samples is normally 4 inches, and in summers like these only an inch or two may contain viable roots. If the problem is more deeply rooted, say 10 – 16 inches below the turf surface, the real cause of the constantly saturated soil is more difficult to decipher. A collapsed PVC plastic drainage pipe is often blamed as a potential culprit, and camera scopes are used to investigate and determine if it’s the true problem. The question that is less often answered is “Does the entire column of soil operate like a perfect flowing tube to the drainage pipe?
The USGA putting green profile is not a flowing tube and isn’t designed as such. The pea gravel layer underneath the sand serves to provide a perched water table, holding a reserve for potential root use until gravity overcomes the water holding force, prior to complete saturation. When gravity takes over, a vacuum pull from the drainage pipe can drain the profile quickly. Some saturate the rootzone on purpose intermittently throughout the season to “flush” potential salts or contaminants, particularly in arid regions prone to salt accumulation.
Research at the University of Wisconsin by Dr. Doug Soldat and University of Nebraska by Dr. Bill Kreuser and his PhD student Glen Obear has uncovered a problem in several USGA putting greens caused by the formation of impermeable iron-oxide layers (click here to read more). This issue is occurring near the sand/pea gravel interface where water and potential contaminants may accumulate. This research is ongoing and hopefully the scope of the problem and potential answers can be realized. The finding begs the question though, how much do contaminants play a role in plugging up the USGA sand profile, and what inputs may be causing their accumulation? If water sits on top of this perch, is it contributing to an anaerobic (or dead bird) state deep in the profile and what harm may this be doing to the above bentgrass?
We often associate turf loss at green margins and collars to increased traffic from mower or golfers, with the worst decline often at the lowest points of the green. Perhaps the lateral subsurface flow of water, however, is causing an increased accumulation of water and flow-inhibiting contaminants in this region near the gravel layer. Additionally, a heavier textured soil serves as a boundary on one side, so if the water is also sealed below where does this subsurface water go? Sitting water results in anaerobic conditions, and potentially a sulfur/methane producing black layer region releasing toxic gas upwards. Additionally, a completely saturated rootzone that doesn’t drain effectively would be a prime ground for Pythium root rot and other soilborne diseases.
Many more questions than answers are presented here, but after an intense summer like this past one, perhaps it is necessary to dig a little deeper. With the brutal environmental conditions this previous summer, bentgrass putting greens needed no extra help in declining. Perhaps the whole solution can’t be achieved from actions on the surface, and the true problem lies farther beneath the surface than we think.
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Extension Turfgrass Pathologist
University of Missouri