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Preemergence Weed Control in Bentgrass Putting Greens

(By Jared Hoyle, KSU Turfgrass Research and Extension)

In the previous post about preemerge herbicides there is a table of many preemergence herbicides that available for professional turfgrass managers.  But when we start talking bout preemerge herbicides that we can use on bentgrass putting greens the list gets really short.  There are not many options out there for PREs on creeping bentgrass putting greens due to the injury they can cause to the putting surface.

Every golf course superintendent knows that one of the main priorities on the golf course is the putting greens. Therefore, weed control on the putting greens is a priority as well.  So lets just to go over some of the PREs that are labeled for creeping bentgrass putting greens and I will also mention one comment about each.

  • bensulide (Bensumec 4FL, Pre-San 12.5G, Weedgrass Preventer) – With this product you are not able to reseed for 4 months and do not use on greens that have more than 50% annual bluegrass.
  • bensulide +oxadiazon (goosegrass/crabgrass control) – To prevent injury apply two half rate treatments 10-14 days apart.
  • dithiopyr (Fertilizers w/ dithiopyr) – Older bentgrass varieties may result in undesirable injury.
  • siduron (Tuperson) – May be applied at time of seeding or to established creeping bentgrass for crabgrass control and bermudagrass suppression.

Also, you can see the list is a lot shorter then the list in the previous post but that is why managing bentgrass is so difficult.  Turfgrass managers must to do whatever they can to have a healthy growing creeping bentgrass system to prevent weeds coming in because once they are there, there isn’t many options to git ride of them.

Information in the previous list was acquired from “Turfgrass Weed Control for Professionals” by A. Patton and D. Weisenberger, Purdue University (and 11 collaborating states including Kansas). For more information about purchasing this publication see;

https://blogs.k-state.edu/turf/new-weed-control-publication-for-turfgrass-professionals/ 

Always remember to READ THE LABEL for the correct rate, turfgrass tolerance, and specific instructions before application!!!

***Mention of trade names or commercial products in this article is solely for identification purposes and does not imply recommendation or endorsement, nor is criticism implied of similar products not mentioned by Kansas State University.***

Don’t forget to follow me on twitter @KSUTurf.

Also, visit our facebook page www.facebook.com/KSUTurf

USGA’s Bob Vavrek gives insight on the “Turf Trifecta”

Bob Vavrek explains how the hot humid weather finally has made life miserable for maintaining cool-season turfgrass putting greens.  There are options out there to help out your putting greens but you always want to make sure to minimize injury to the turf during these stressful times.

Check out the article on the USGA website here.

http://www.usga.org/course-care/regional-updates/central-region/the-turf-trifecta.html

 

Water Management on Greens with Soil Moisture Sensors

After last week’s posts, I got several follow-up questions by phone and email on how to use moisture meters. Dr. Bremer is our microclimate guru, so I asked him to provide some pointers. – Megan Kennelly

 

How much water is too much or too little for your greens?

 

By Dale Bremer

As Dr. Jack Fry discussed in his recent article on this blog Good Water Management Will Help Get Greens Through Summer Stress, too much or too little water can be detrimental. I thought I would follow up with a few practical tips on how to determine the correct amount of water for your green using a soil moisture sensor that determines volumetric water content. The most common soil moisture sensor is probably a TDR (time domain reflectometry) such as the one shown in Figure 1. Keep in mind that different depths (lengths) of probes are available, and that you are primarily interested in measuring soil moisture in the root zone; any moisture that is below the root zone is unavailable to the plant. The depth of the root zone may vary during the summer (shallower in midsummer, deeper in spring and fall), but a good compromise would probably be the 3 inch probes.

Fig1

(Figure 1)

 

Ideally we should avoid constantly saturating soils with water. Instead, allow them to dry down to a predetermined level of soil water content just before the onset of drought stress symptoms. By definition, soils are saturated when 100% of the soil pore volume is filled with water. After irrigation, the soil will eventually reach field capacity, which is the amount of water remaining in the soil after free drainage has ceased. At field capacity, soils have good aeration but also have sufficient water for plant use. General guidelines for the volumetric water content at field capacity are 15-20% in sandy soils, 35-45% for loam soils, and 45-55% for clay soils (1).

On the other end of the scale, permanent wilting point is the soil water content when plants wilt and don’t recover when the soil is rewetted. Obviously this should be avoided in a green! Textbook values for volumetric water content at the permanent wilting point are 5-10% for sandy soils, 10-15% for loam soils, and 15-20% in clay soils.

However, for a number of reasons soil water content values at field capacity and permanent wilting point may vary from the textbook values for your green. This could be caused by differences in sand particle size, organic matter content, age of a green, etc.

A simple way to determine how much water to apply to your greens is to calibrate your soil moisture probe to your soils with the following steps:

  1. Irrigate the turf thoroughly, then take readings with your soil moisture sensor one hour later. Measure in several spots around your green, perhaps even in a grid pattern as you see fit.
  2. Take readings twice daily and note visual stress symptoms of the turf.
  3. Continue taking readings until turf shows symptoms of drought stress.
  4. Once these levels have been determined, use them help guide future irrigation events.
  5. Calibrate for each soil type.

My colleagues at the University of Arkansas (Doug Karcher and Mike Richardson) (2) used this method on native soils and on 1-year old and 10-year old USGA greens and came up with the dry down curves in Figure 2.

graph

Although soil moisture levels in the 10-year old green are higher than the 1-year old green, it is likely that drought symptoms begin at a higher soil moisture content in the 10-year old green; the same is likely for the native soil. This illustrates why it is a good idea to calibrate separately for different soils and for greens that may differ in age. It’s also important to note that drought threshold levels may change through the year, as the root system changes (as alluded to above). For example, a shallow root system in midsummer may require that irrigation be applied at a higher soil water threshold because roots are not able to “mine” water deeper in the soil as they may have earlier in the growing season.

References:

  1. http://nrcca.cals.cornell.edu/soil/CA2/CA0212.1-3.php
  2. http://www.stma.org/sites/stma/files/Conference/2012_Conference/Karcher.pdf

Good Water Management will Help Get Greens Through Midsummer Stress

by Jack Fry, KSU

It’s like watching a toddler play with an open staircase nearby. You’re in a good mood and things are going reasonably well, but if you turn your head away for an instant, disaster could strike. It’s no different than managing water on putting greens during midsummer. Minor flaws in greens construction or management may go unnoticed until now; when temperatures are 85 degrees or lower, bentgrass is able to tolerate it. But, an extended stretch of 100+ degree days highs, along with high night temperatures, can bring out the weaknesses in construction or the superintendent’s management program. A rootzone that remains wetter longer can exacerbate problems. Maybe you’re dealing with push-up greens that have been topdressed for years with sand; better than nothing, but not as good as a well-constructed, well-drained profile. Maybe your greens were constructed to “almost” – USGA specifications. For example, maybe sand particle size wasn’t evaluated by a testing lab, pea gravel doesn’t meet specifications, or the rootzone is 8 inches deep on some parts of the green and 15 inches deep in others. Perhaps your topdressing sand particle size distribution, or frequency of application, are different from the previous superintendent. All of these factors can contribute to the rootzone holding too much water, or not enough.

A rootzone that stays wet too long will have limited oxygen, and also be hotter than one that drains well (water helps retain heat); neither situation bodes well for bentgrass roots. Optimum bentgrass root growth occurs at 50 to 65 F. The top two inches of most putting surfaces in full sun during mid-day during July in Kansas will be 90 degrees or higher. Up until now, we have had excessive rainfall, and roots of bentgrass and annual bluegrass on many greens are no deeper than a couple of inches, particularly if the rootzone retains more water than desired. Furthermore, the roots that are there may not be functioning at an optimum level with the ongoing heat. The plant’s water-absorbing capability has been severely limited (it’s like being really thirsty with a cold glass of ice water in front you, but you’re not able to swallow). The “deep and less frequent” strategy for irrigation is not going to be effective when roots are shallow or not effective at taking up water. Instead, match frequency of irrigation to rooting depth, which could mean irrigating at least once a day.

Frequent scouting of greens will help identify areas that are experiencing stress first – the purple/blue color is a good indicator. Lightly watering these areas by hand will help make up for deficiencies in water distribution by the irrigation system and differences in the rate the turf uses water across the surface of the green. Pay particular attention to sloped areas that dry out faster. Hydrophobic localized dry spots will continue to exhibit stress symptoms unless a wetting agent is used in combination with probing the areas to encourage water penetration. The ability to hand water correctly is not something we’re born with – train your best people how to effectively scout and to apply the right amount in the right places. Hand-held soil moisture meters are becoming commonplace for determining volumetric water content of greens (Fig. 1). If you don’t have one, put it on your wish list. By using the probe, you or your employees will be able to identify areas of the greens that are drying faster and need water, or those that are moist enough that watering should be avoided.

 

Presentation1

Fig. 1. Soil moisture meter for measuring uniformity of rootzone water content across the putting green.

 

Syringing, supplying a light mist on the surface of the leaves, can be used to help cool the leaf’s surface. However, it’s most effective when the humidity is lower and/or if there is air movement to help the water evaporate. Thin out or remove trees, or install fans, before relying on syringing to get creeping bentgrass through periods of heat stress.

Managing water on greens in midsummer is tricky business. Pay attention, put up a gate, do whatever it takes to keep the toddler away from the staircase.

More info on physiological decline and diseases

(By Jared Hoyle; KSU Turfgrass Research and Extension)

One of my good friends on the other side of the river at the University of Missouri, Dr. Lee Miller, has posted some great information about physiological decline and updates on diseases that he has been seeing.

For more information on physiological decline/ wet wilt of bentgrass greens check this out – “Summer Rises” – (It’s at the bottom of the article)

http://turfpath.missouri.edu/reports/2015/update07_13_15.cfm

For more information on diseases and more specifically brown patch control see Dr. Miller’s most recent post – “Rhizoc, Rinse, Repeat” –

http://turfpath.missouri.edu/reports/2015/update07_28_15.cfm

IMG_2314

 

Summer weather can be ruthless when the turf is stressed and rootless

019 020 hydrophobic-droplet-test thatch_layers

(Megan Kennelly, KSU Plant Pathology)

Losing turf and having a hard time getting it back? You aren’t alone.

It’s that time of year when turf can quickly fall into a tailspin, especially putting green turf. In the past 1-2 weeks, the number of emails, phone calls, and samples has really spiked. Jack Fry has provided a great article with tips about watering bentgrass elsewhere on the blog this week (see http://blogs.k-state.edu/turf/good-water-man…dsummer-stress/) and we  have also linked to some excellent info from Dr. Miller in Missouri (https://blogs.k-state.edu/turf/more-info-on-physiological-decline-and-diseases/). Here, I will talk about a few other topics related to summer stress in turf.  The next stretch of days are looking better with cooler highs as well as some nighttime lows in the 60’s, but the summer heat will probably be back before it’s gone for good.

Take a look at your rootzone.

If you are seeing turf decline above ground, take a peek above ground. I’ve seen a number of samples lately where the rootzone shows some clear underlying problems of organic matter buildup, thatch, or localized dry spot. I posted some example photos up above, at the top of this post. Your situation might not be as severe as those, but consider whether rootzone management could be the culprit behind the decline.

Summer heat is NOT the time to get aggressive with aerification, but put it on the agenda as a priority for fall.   Throughout the fall and next spring keep on with the best agronomic practices you can manage. Build up those roots when the turf is growing its best, during fall and spring temps. Building up the turf is like putting money in the bank to rely on during the tough times (ie, July and August of 2016). In the meantime,with cooler spells (highs in the 80’s for a few days) you can consider some gentle aerification with solid tines but be careful! Try to do it during cooler parts of the day. Watch the turf and stop operation if the turf can’t take it and is getting torn up.  We may be a long way from weather that will allow long-term recovery.

Does your profile look like a layer cake? Put some aerification and topdressing on the agenda for fall.

layers and aeration hole

 

Look at the roots, since they’re supporting the shoots

In addition to problems in the soil profile itself, there have been multiple samples where the roots themselves are short, brown/mushy, and lacking root hairs. Sometimes there is a root pathogen thrown in there, sometimes there isn’t and it’s just physiological decline. Either way, the turf is suffering.  How deep are your roots? Are there lots of root hair that cling to the sand, or does the sand slide right off? Try washing the soil off of a plug or two. Healthy roots are a creamy white. Brown and mushy? That’s not good. Before you start treating what looks like an above-ground problem, take a peak under the ground.

Check your roots and plan ahead to build more for NEXT summer

turf_shortroots_longroots

Brown and mushy is not good

mushy

 

Hot underground = little growth to be found

When it’s 100 degrees outside in the air, we feel it. But, what the turf is really feeling is heat in the soil. When soil temps get into the upper 70’s and 80’s, root growth starts to shut down. When soil temps get into the 90’s, shoot growth stops too. What this means is that if you have any damage from disease/insects/stress, the turf will have a hard time growing out of it.

Use a soil thermometer to check your soil temps. It may not be pretty. The next week or so will give us a nice break, though.

 

Too much water can be worse than not enough.

If the soil is wet, it holds more heat so turf does not cool off well overnight, and this can really trigger a spiral of decline.  Check Jack’s article for some tips (http://blogs.k-state.edu/turf/good-water-man…dsummer-stress/)

 

“I sprayed a fungicide and it didn’t seem to work”

Okay – let’s talk about diseases for a minute. You might be seeing dollar spot, brown patch, anthracnose, or Pythium root rot. For this discussion, let’s assume that you diagnosed it correctly and applied a great chemical at optimal rates with impeccable coverage.

But – you still might not see improvement. In fact, the disease could still get a little worse at first. Keep in mind, diseases have a latent period, and there could be more “infected” tissue than “symptomatic” tissue. So, for a couple of days, you could still see some symptoms develop from tissue  that was actually colonized before you even knew it and got the product down.

Then, once that phase is done, even with the pathogen shut down and not infecting more tissue, you still have the problem that the turf isn’t growing well. That is, you might not have new green, good-looking turf for awhile even if the disease itself is under control. The aesthetics won’t improve until there is some new growth to fill in the damaged areas. Hopefully we will get some recovery in the next few days, with the milder temps.

As a final point on fungicides (and any product), be very careful to heed any warnings about use in hot weather. Test any new tank-mix concoctions on a small scale first to avoid unfortunate surprises. There are some excellent details about specific products in this publication: http://www2.ca.uky.edu/agc/pubs/ppa/ppa1/ppa1.pdf

 

Got Poa?

Annual bluegrass is pretty wimpy stuff. Here it is checking out in the heat:

poa dying

Poa triv is checking out, too. If you have problems with these pesky invaders try to reduce their populations for next year.  It’s easy to forget about them a little bit when everything is green and happy, but there’s no ignoring them now.

Do you become a little more devout in August?

Over the years, I’ve heard several superintendents say variations of, “God grows the turf from Labor Day through Memorial Day. Then, it’s our job June, and July… and August? That’s when we start to pray.”

The next week or so is looking better, and maybe we will be lucky and August will be mild. Let’s hope so.

GDD Tracker for Poa annua Seedhead Suppression

(By Jared Hoyle, KSU Turfgrass Research and Extension)

Annual bluegrass in a bentgrass putting green
Annual bluegrass in a bentgrass putting green

Golf course superintendents in KS typically have to manage annual bluegrass in putting greens and not so much “control” it because of the large populations of annual bluegrass that exist in the putting greens.

One of annual bluegrass management practices is the use of PGRs. This is combination with aerification, pre-emergent herbicides, fertility and proper irrigation management, just to mention a few, can lead to the success of reducing annual bluegrass populations and increasing bentgrass incidence.

Timing of the PGR applications in the spring can be one of the most difficult tasks. Too late can lead to a summer of playing catch-up. The use of Growing Degree Days (GDD) can really help predict PGR application timings.

http://www.gddtracker.net/

Just type in your location on the “Proxy/Primo Seedhead Timer (GDD 32)” page and it will give you the GDD in your area. Earlier applications have seen to be more effective than later applications so try and get a Proxy/Primo application out after two mowings (full green-up) or 200-250 growing degree-days on the GDD 32 model. The Target Range is 200-500 but greater success has been seen when the initial application was made earlier. In 2014 Manhattan, KS reached 200 GDD (base 32) on March 15th.  Right now Manhattan is at 5 GDD.  But watch out it can catch-up real quick!

Research conducted out of MSU suggests that tank mixes of Proxy/Primo for Poa annua Seedhead Suppression on bentgrass greens should be made at 5 + 0.125 fl oz per 1000ft2. A repeat application can be made 21 days later. If golf course superintendents plan on applying Primo throughout the season then they can start their program 14-21 days after the tankmix treatment.

Information contained in this blog can be found at http://www.gddtracker.net/about ; Dept. of Crop and Soil Sciences, Michigan State University.

Always remember to READ THE LABEL for the correct rate, turfgrass tolerance, and specific instructions before application!!!

***Mention of trade names or commercial products in this article is solely for identification purposes and does not imply recommendation or endorsement, nor is criticism implied of similar products not mentioned by Kansas State University.***

Don’t forget to follow me on twitter @KSUTurf.

Also, visit our facebook page www.facebook.com/KSUTurf

Dollar spot activity

The moderate temperatures are reducing stress on our cool-season turfgrasses, and some of our typical late July/early August diseases are not active. Dollar spot likes this type of weather and it IS active. Here is a picture of a nontreated plot out at Rocky Ford:

Keep on your disease management plan, and don’t forget some back-to-basic things like calibration, swapping out worn-out nozzles, etc.  I spoke with someone recently where it sounds like some application/calibration issues might have compromised disease control.