It’s Almost Time to Prevent Large Patch!

With soil temperatures starting to approach 70°F across portions of NC, now is the time to start thinking about treating for large patch.

Average Daily Soil Temperature on 9/14/11 from the NC State Climate Office

Large patch, which is caused by the fungus Rhizoctonia solani, is a common disease of centipedegrass, St. Augustinegrass, zoysiagrass, and bermudagrass grown for lawns, landscapes, golf turf, and athletic fields. Centipedegrass and St. Augustinegrass are particularly susceptible to this disease.

Symptoms of large patch appear in roughly circular patches from 2 feet up to 10 feet or more in diameter. The affected turf will initially be orange, yellow, or reddish-brown in color but will then turn tan and collapse to the ground. The disease can spread rapidly to encompass large areas of turf, and distinct circular patches may not be obvious in these cases.

Fungicides are available for large patch control, but they must be applied preventatively for best results. The first application should be made in the late summer or early fall when average daily soil temperatures are 70°F or below. Depending on your location and weather patterns, this can be anywhere from late August to late September.

One fungicide application will control minor cases of large patch, but two to three applications on a 4 to 6 week interval may be needed to control severe cases. Fungicides are not very effective once the symptoms of large patch appear. Curative applications will help to reduce further spread of the disease, but the affected turf will be very slow to recover.

Click here for more information about Large Patch, including images and specific control recommendations.

Getting ready for life without Rubigan

Is this what life will look like without Rubigan?

A lot of people have heard about Rubigan going off the market in December 2012. If you have questions or concerns, please check out yesterday's post on turfdiseases.org entitled "What will we do when Rubigan is Rubi-gone?".

We are planning a lot more spring dead spot research this fall in response to this issue, so we'll probably be in touch with some of you about the possibility of doing research at your facilities.

Do growth regulators and biostimulants cause yellow etiolation of creeping bentgrass?

We've been seeing yellowing and etiolation of creeping bentgrass greens in North Carolina off and on since 2005. Some people are calling this 'bacterial wilt', but there are two problems with this name. First, no one has proven that this condition is caused by a bacteria. Second, and perhaps most obviously, wilt isn't one of the symptoms!

So, can we all agree to call it yellow etiolation instead of just slapping another erroneous name on it? I know that 'etiolation' is difficult to pronounce, but you can hear its correct pronunciation and practice along at thefreedictionary.com/etiolation.

Early on, I had a theory that biostimulants and/or growth regulators were involved in either causing this yellow etiolation or increasing its appearance. I wanted to share a couple of pictures recently sent to me by golf course superintendents that provide even more evidence of their role in this condition.


This first picture was taken at one of our research sites. Our plots were positioned in a ring around the cleanup pass of this green, and we asked them to avoid spraying our plots when they made certain applications to the greens. The area to the right that is declining severely received their sprays containing a biostimulant product and the growth regulator trinexapac-ethyl. As you can see very clearly, the areas NOT receiving these sprays are much more healthy than the areas that were sprayed.



This second picture was sent to me by a golf course superintendent in Pennsylvania. You are looking at a collar-height walkway between a green and a tee. The area to the left of the red dotted line received double applications of Primo, one along with the greens applications and another along with the tee applications. You can clearly see that the yellowing, etiolation, and thinning of the bentgrass is much more pronounced in the area receiving higher rates of Primo.

So what is going on here? To me, this is looking more and more like a physiological condition rather than a disease problem. We are still unable to consistently isolate any single pathogen, bacteria or otherwise, from turf exhibiting these symptoms. We are planning research to look at the influence of growth regulators and biostimulants on this problem. Until then, I suggest that superintendents who are battling this problem eliminate biostumulants from their programs and also avoid use of trinexapac-ethyl during periods of summer stress.

Program '11 Update: Stress

A lot has happened since the last update I posted on July 22. We had record attendance of 650 at our NC State Turfgrass Field Day on August 10. Classes are in session, conference season is starting up, and we had an earthquake AND a hurricane in one week. I sincerely hope that everyone who was in the path of Hurricane Irene escaped severe damage.

From mid July to mid August was hot, humid, and stressful for bentgrass putting greens in North Carolina, with 18 days above 95 and 6 days above 100. The low temperature only dipped below 70 degrees once during this time.

We've made several changes to Program '11 in response to the prevailing weather patterns. In response to the severe stress imposed by the weather conditions, we decided to apply Signature + Daconil on August 1 instead of Stellar + Daconil. On August 15, the weather was cooling off and we decided to drop the Alude application and applied Spectro alone.

On August 29, in the wake of Irene, we applied Honor instead of Subdue + Fore. While there was some potential for Pythium root rot development in these wet conditions, we were more concerned about the explosion of dollar spot and brown patch we were observing in untreated areas on the research farm.


All of the programs have continued to provide excellent disease control. No significant amounts of dollar spot, brown patch, anthracnose, or Pythium root rot have been observed in the treated plots. The Bayer Program has continued to express more yellow spot symptoms as I reported in July. This program contains a lot of QoI fungicides, which we've found increase the intensity of yellow spot symptoms.

On July 25, Program 13, NC State Program, BASF Program and Program '11 all exhibited excellent turf quality. Beginning in early to mid July, all programs declined in their turf quality, except for the BASF program which actually continued to slightly improve. Plots treated with the BASF Program has significantly better turf quality than all others on August 16 and 22. The Syngenta Program improved in its turf quality and by August 29 was statistically similar to the BASF Program while all the others were significantly lower.

It is difficult to determine why the BASF Program held up so well during the hot and humid conditions of early July. These plots were treated with a tank-mixture of Segway, Iprodione Pro, and Daconil Ultrex on August 8, which may have helped to control some underlying Pythium root rot or other disease. Perhaps the application of Honor on July 11 helped to precondition the bentgrass for the oncoming stress as BASF promotes.

Program '11 Update: Yellow Spot

As mentioned in a previous post, yellow spot has been particularly bad this year on creeping bentgrass putting greens. We have a lot of it in our Program '11 Trial area so we were able to assess how fungicide programs are influencing the disease.

It is interesting to note that the programs receiving chlorothalonil or mancozeb applications during May and June were relatively clean of yellow spot, especially the Syngenta, BASF, and Program '11 treatments. This is consistent with our past observations of effective yellow spot control with chlorothalonil and mancozeb.


For the most part, we stuck to our original plans for Program '11 during July. Most of the changes we make continue to be dictated by dollar spot pressure. We applied Disarm C instead of Honor on June 20 because the Honor was applied earlier on June 6. We also applied Signature + 26GT on July 5 instead of Signature + Daconil Ultrex because dollar spot was continuing to develop and we feared that Daconil alone would not provide sufficient control. Both of these changes may have turned out to be a mistake.

Turf quality dipped to 6 out of 9 in our Program '11 treatment on July 19. Turf in these plots was showing significant signs of stress, thinning, and algae invasion. On the other hand, the NC State Program was among the best treatments in the trial with turf quality of 7 out of 9. The Honor application on June 20 and the Signature + Daconil application on July 5 are most likely responsible for the increased turf quality provided by the NC State Program.

Now entering the 'No DMI Zone'

Every year, we see a lot of golf course superintendents get into trouble by applying DMI fungicides to bentgrass or Poa annua putting greens during periods of hot weather. These products can cause severe damage to stressed cool-season grasses, and our general rule of thumb is that they should not be applied to putting green turf when temperatures above 90 are expected in the next two weeks. After a nice break in the weather late last week, temperatures are ramping up into the high 90's and I don't think we can count on seeing temperatures below 90 for quite some time.

There are few good reasons to apply a DMI fungicide during July and August anyway. Most of our summer diseases can be controlled very well with other chemistries that do not have these negative side-effects.

So, if you are considering an application of a DMI fungicide, ask yourself two questions: "Are my greens stressed? Are temperatures above 90 in the forecast?" If the answer to either of these questions is "Yes", then leave the DMIs on the shelf!

One exception is anthracnose; if you have Poa annua greens or older bentgrass varieties that are prone to anthracnose, a DMI application could be justified. The new-generation DMIs like metconazole, tebuconazole, and triticonazole have less injury potential on cool-season grasses and provide very good anthracnose control. Keep the rates low and tank-mix with chlorothalonil to minimize the chances for injury, thinning of the turf, and algae invasion.

Update on Bacteria in Creeping Bentgrass Greens

In the last month, we've observed significant amounts of bacteria in 32 creeping bentgrass samples submitted to the Turf Diagnostics Lab. We isolated the bacteria in these samples and are identifying them by DNA sequencing and other techniques.

The good news first: the majority of samples contained bacteria that are known to be non-pathogenic to turf. We suspect that these bacterial infections occurred during aerification and topdressings performed after Memorial Day when it was very hot and humid. These non-pathogenic bacteria are not killing the plant directly but may be speeding up the dieback of leaves or tillers that were injured by these stressful practices.

We did isolate the plant pathogenic bacteria Acidovorax from 7 locations, most of which are in the Piedmont of North Carolina. The samples that contain Acidovorax are showing the symptoms of chlorosis, etiolation, and gradual thinning that I wrote about in previous posts. The caveat is that we're not isolating Acidovorax from all of the locations where these symptoms are present. As a result, we cannot be sure that this bacteria is the true cause of the symptoms.

Results from trial on L-93 in Raleigh. Rates are per 1000 sq ft.

We have ongoing trials at 2 locations where Acidovorax is present, and our preliminary data is presented here. First, a word on our rating scale. These ratings are on a 0 to 9 scale, where 0 equals no disease, 1 to 3 represents varying degrees of chlorosis, 4 to 6 represents chlorosis with varying degrees of thinning, and 7 to 9 represent severe thinning of the turf.

Results from trial on G-2 in Charlotte. Rates are per 1000 sq ft.

While we haven't found a silver bullet yet, we have noticed that Signature treatments seem to be helping. In the Raleigh trial, 8 oz of Signature applied 3 times has prevented the turf from thinning, although some chlorosis and etiolation is still evident. In the Charlotte location, plots treated with 8 oz of Signature 3 times have improved slightly, while all other plots have continued to thin.

Before you complain about the price of an 8 oz Signature spray: we don't set the prices, we're just trying to find something that works. We are continuing to evaluate other products and practices that may help to control this problem and will post regular updates on this blog as we learn more.

One important take-home message: just because a diagnostic lab sees bacteria in your bentgrass doesn't mean you have a bacterial disease. Most of the samples we've received have only contained non-pathogenic bacteria. The bacteria has to be isolated and identified in order to determine if it is a plant pathogen.