When Bentgrass Bonks
MU Turfgrass & Landscape Field Day – Next Tuesday!
Click here to register.
Guide Offered at Field Day
As Spiderman would say, "everyone gets one" when you attend the 2019 MU field day.
If you need any more reason to attend next week's field day, while supplies last we will be offering the above guide to each attendee. Pest Management for Home Lawns is a pocket- or glove box-sized manual that can be used by lawn care operators to facilitate dialogue with homeowners on the common pests that harm lawns in Missouri and how to manage them. It is also part of the core curriculum for our Lawn Care workshop series previously held in STL, KC, and Springfield with future iterations on the way. For any turf manager working with higher cut turf, the guide is handy and with Dr. Brad Fresenburg and Dr. Bruce Barrett acting as co-authors a ton of expertise is wrapped up into a small space.
A big thank you to all of the exhibitors that will be in attendance, whose support gives us the opportunity to provide the education and for you to be able to find the applicable solution on site. A full list of exhibitors can be found here.
Click here to see the entire schedule.
- High temps got the billing last week, but high night temps steal the show. – Missouri Climate Center
- The current cool down looks to be temporary. – NOAA
Echoing Ron Burgundy, "well that escalated quickly". Summer heat and humidity arrived in force last week, meaning sweat of cool season turf managers was produced by both environment and nerves. As shown above, while the high daytime temperatures dramatically spiked, the above average nighttime temperatures have been riding steady all month long. This means high dewpoints, and lots of dew, facilitated foliar summer diseases. But also equated into virtually no break for poor bentgrass roots to grow in water logged, boiling root zones (more on that below). The very welcome break in temperatures we experienced this week is set to end as we get into the first of August.
July may be breaking the trend a bit in rainfall frequency, but precipitation have been very spotty. Considerable rainfall has impacted the southwest portion of the state in July, while other regions were (dare I say it) nearly in a drought situation after the 1st wettest May and above average June. Rainfall chances increase next week, with a system set to move in Sunday and Monday, hopefully a break for field day on Tuesday, and then higher chances into late week.
July Rainfall Varies Across the Region
- Believe it or not, drought symptoms nearly occurred in mid July. – Missouri Climate Center
- Rainfall chances increase next week. – NOAA
Abiotic Injury & Pythium root rot
- Easy to observe in this plug where air gets in, and the bentgrass health benefits.
- Root decline leads to higher OM, wetter soils, and Pythium root rot.
A term used by some runners, "bonking" is when the energy expended on long runs is beyond the calorie intake and corresponding energy level. One gets disoriented, light headed and dizzy, so it serves as a perfect term for bentgrass putting greens in this environment. The advent of real summer stress weather last week, with sustained high daily and nighttime temperatures and persistent humidity, brought in a flood of bentgrass putting green samples this week. At this point, a perfect ten samples have been submitted, and it just so happens to illustrate quite perfectly the approximate percentage of diagnoses from most summer submissions.
- Abiotic/Physiological Decline: 100%. Obviously it can't be 100% and match up with the others, so one might consider it to be 70%. However, the rootzone environment is the major predisposing factor to symptom development due to soilborne diseases this time of year. Therefore, it's impossible to exclude from the diagnosis. As stated in earlier reports, water in the soil profile is normally the villain here. Saturated roots don't have oxygen available in pore spaces to respire and grow, and toxic gasses get trapped in the soil where they further inhibit root growth. Water that gets hot tends to stay hot, resulting in higher nighttime soil temperatures when roots need the break. Water also provides a perfect breeding ground for soilborne pathogens and facilitates dissemination, particularly for the water mold Pythium. Pathogens that are all too primed to prey on high temperature and water weakened roots and crowns.
Too much water in the soil profile of putting greens is often part of a vicious cycle. Organic matter holds on to moisture like a sponge and "normal" physiological root decline adds to the normal levels of OM, so more builds up as the summer rolls along. As the soil moisture builds and heats up more roots and older leaves die contributing to the accumulation. Black layer caused by anaerobic bacteria may also take a foothold, as may toxin producing algae towards the soil surface.
Some techniques during the summer to help include:
1. Irrigation Management - Be careful with the amount of irrigation applied, particularly in rainfall events. Keep overhead irrigation to a minimum, and consider using TDRs to assess volumetric water content.
2. Topdress - Effectively shortens mowing height while not dropping a blade, but also dilutes organic matter from the top down.
3. Solid tine/vent - Put it on a regular schedule with a tine size and type that makes the most sense considering the condition and stress level of the green. We often talk about "babying" a green during summer stress periods. Well, babies need to be burped or they will throw up. So burp your greens.
4. Pull cores or slit when turf is actively growing and create sand-filled channels.
5. Last but not least, restrict verticutting on bentgrass and move to solid rollers.
- Pythium Root Infection – 20%. While present in most samples, Pythium root infection is the major cause of root decline in about 20 – 30% of samples, and these past 10 samples had two bonafide Pythium root rot caused decline symptoms. This leads to a bit of judgement during diagnosis since the environment is often also playing a major role. If the oospores are numerous enough to persistently wink at me in the microscope and roots are clouded with encysting zoospores, then a Pythium targeted fungicide application would aid recovery in my estimation. Cyazofamid (Segway) is still the heaviest hitter relied on most often for curative activity at the 0.9 fl oz/M rate tank mixed with a QoI fungicide, but should also be considered in the spring and summer at the half rate for prevention (particularly during this wet May and June) . Etridiazole (Koban/Terrazole) is often suggested as a knock down curative application, and may serve in a rotation preventively along with other Pythium fungicides like Signature, Subdue, Banol, etc. These fungicides must be watered in with at least 0.1 inch of irrigation and perhaps higher volumes depending on root depth and organic matter.
- Summer patch added on to the stress of hot, humid conditions to result in
- Infected root and root base of infected plant.
- Summer Patch – 10%. This is another soilborne disease along with take-all patch in which the pathogen can always be found lurking around stressed roots. Symptoms may occur as rings or frog eyes or in severely affected turf as distinct patches. Infected roots have a very darkened root cortex all the way to the stem base, and ectotrophic hyphae course along the outer epidermal cells producing scattered infection cushions along the way. For curative activity, Briskway, a multiple action DMI and QoI fungicide is suggested at the high 0.75 fl oz/M rate. A small dose of ammonium sulfate (~0.15 lb N/M) may also aid recovery, but should be used with some care in summer if a black layer problem is already present. As with the Pythium root rot fungicides, these should be watered in.
Last but not least, greens can and often do have a combination of one, two, or all three issues that may be predicated by parasitic nematodes. But that will be a story for another time.
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Extension Turfgrass Pathologist
University of Missouri