Wet & Hot July 2016
The adage “if you don’t like the weather in Missouri just wait a few minutes” definitely applies to this summer thus far. July 2016 will be remembered as one of the bigger shifts in monthly rainfall patterns in sometime. June was extremely hot and dry, while July is giving us a healthy dose of the Amazon, with a sustained heat accompanied by a ton of rain. July temperatures are approximately a degree or so above normal, but the real story has been the heavy rainfall, particularly along the state’s midsection. Over 10 inches have officially fallen in many locales (some report northward of 17 in.), with Columbia already having the 5th wettest July in recorded weather history. Overall the state average is around 6 inches which ranks 12th (July 2015 ranked 4th). July is typically one of the drier months of the growing season in Missouri, so to have two years with extremely above average rainfall in a row is very rare. Thank you as always to Dr. Pat Guinan for helping to accumulate this information.
As we roll into August, (and thankfully for some shorter daylengths), the forecasted weather pattern in the early portion for the month seems to be more of the same. A return of warmer temperatures is expected to return next week, with healthy chances of rainfall. As demonstrated below, many turfgrass diseases are currently active and I expect them to remain so for the early part of August.
Early August Outlook
Brown Patch Raging Now
“Other” spots aren’t sitting around
Samples of declining bentgrass putting greens have flooded into the MU Plant Diagnostic Clinic over the last two weeks. This persistently terrible weather pattern for bentgrass health has taken an extreme toll on the health of these cool season plants that are perilously trafficked, groomed, and cut at marginally sustainable heights. Many are also facing maintenance heavy and high expectation tournaments in late July or August, which are doing no favors.
Below are the three most often observed problems on bentgrass putting greens we’ve seen in the Clinic over the past month in order of prevalence. Note all of the issues are root related. Management practices should be focused on this aspect during these times of turmoil, while simultaneously not neglecting the normal stress preventers (raising mowing heights, smooth rollers, spoonfeeding, etc.). A preventive soilborne fungicide program is warranted, but also realize the answers to these problems will not solely come out of your sprayer boom. Lastly, the physiological decline of the plant due to inhospitable weather conditions is paramount here. So addressing this first, as I will, can reduce your management inputs substantially for the true biotic issues.
Physiological Root Decline
Air vs. water - the struggle is more than real now in a bentgrass root’s existence. Needs both, but most of the time the overabundance of water is the true enemy. Water excludes air indiscriminately in pore spaces of saturated soils, and then holds a constant temperature for an extended amount of time. Root growth stops at 86 degrees F (30 C), and daily 2” soil temperatures in native soils were averaging 90 degrees and above during this latest heat wave. These water soaked soils simply don’t cool off at night, leaving roots to continually boil. This high specific heat capacity of water keeps fish in the deep pond happy, but won’t keep shallow roots growing in the wading pool of a summer putting green rootzone. Managing greens with a soil moisture meter (TDR) is a good way to dial in the difference between underwatered, adequate, or oversaturated.
Recently, Dr. Bill Kreuser from the University of Nebraska posted a video regarding the cooling effects, or lack thereof, of syringing greens (click here to view). Several superintendents are stopping or considering stopping the practice of cooling off greens with water throughout the afternoon heat and focusing on utilizing morning irrigation only to provide water throughout the day. From a root perspective, this is a wise move, since most syringing practices in my estimation provide considerably too much water into the rootzone during the heat of the day. This water sticks in the organic matter, heats up, and commences to sous vide the short root system for an extended amount of time. Additionally, this excess water provides a suitable environment for soilborne pathogens, particularly Pythium root rot.
The true hero of cooling is air movement. As stated a few times in these updates, fans have been the best, most consistent fungicide and plant health tool I’ve observed. As shown by David Han at Auburn University, fans reduce not only air and canopy temperature, but also soil temperatures by 5 – 7 degrees F. This makes sense when thought of in the air vs. water perspective. Humidity in the air and moisture on the leaf is reduced, allowing the plant to continually move water through its system and out to the atmosphere. Functioning roots in turn pull water out of the soil pores and leaves air, which won’t hold on to that high temperature so stubbornly when the evening hours finally arrive. So break out the generators and box fans on troubled greens to encourage recovery, and put in a request for 220 volts of beautiful wind.
Lastly, venting greens needs to go on your calendar just as much as when to make fertilizer and pesticide applications. This is a crucial water and air management tool for your rootzone during the summer heat, and should be planned biweekly at a minimum. The damage done during the venting process pales in comparison to the damage that will be done if venting doesn’t occur regularly.
Pythium Root Rot Still Widespread
Several samples of “wow” amounts of Pythium root rot have been submitted recently.
In past reports, I have beaten to death the amount of Pythium root rot observed this season. In the last few weeks, several samples of “wow” Pythium root rot infections have continued to come in, indicating again how widespread this epidemic is in the region. A preventive program using watered-in (approximately 1/8 inch) fungicide applications should been in place, particularly in areas heavily impacted by July rains and those that have had a history of the disease. As detailed by Dr. Jim Kerns at NC State University, a 14 day rotational program using Segway (low rate) as a base (i.e. Segway – Signature Xtra – Segway – Banol – Segway – Subdue, etc.) is the current suggestion for controlling this difficult disease. Dr. Kerns will be visiting the MU campus on September 21 to give a seminar to the Plant Sciences Division. Superintendents interested in attending should send me an email for more details.
Summer Patch on Bentgrass
Last, but certainly not least, we have observed a number of cases of summer patch on creeping bentgrass as the primary cause of decline, and also as an “add-on” in root physiological decline. This pathogen begins to infect earlier in the summer (65 F soil temperature) and gradually takes out the root system with summer stress being the final deliverer of symptoms. Stand symptoms appear as mottled, droughty areas. Individual roots have extremely darkened vascular cylinders with symptoms that extend all the way up to the base of the plant. On bentgrass putting greens, a preventive strategy of watered in applications of QoI fungicides (Heritage, Insignia) or mixtures with QoI fungicides (i.e. Briskway, Lexicon) are recommended.
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Extension Turfgrass Pathologist
University of Missouri