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.

Program '11 Update: Dry and Cool

It's been dry in Raleigh during most of June, and cool (compared to last year, at least) for the last couple weeks. Disease pressure on our 'A-1' bentgrass green has been relatively light as a result. Nevertheless, we still made several changes to Program '11:

Dollar spot pressure was still pretty high in early June, so instead of applying Disarm C on June 6 we applied Honor for its better activity against dollar spot. We skipped the application of Subdue Maxx that was planned for June 13 because of the dry conditions. Then on June 20 we applied the Disarm C that was originally planned for June 6.


All of the programs are providing good brown patch control. Dollar spot is still reducing turf quality in the Syngenta Program, but all other programs are providing very good turf quality this week.


For more information about our Program '11 Project, or to follow along on Facebook or Twitter, please visit our website turfpathology.org.

If it's yellow, just be mellow

Rumors have been swirling around the golf industry over the last week about 'bacterial wilt'. For the record, I want to make it clear that we have diagnosed NO cases of bacterial wilt in North Carolina or any other state.

I repeat, we have diagnosed NO cases of bacterial wilt in North Carolina or any other state.

Yellow spot of creeping bentgrass.

We have seen suspicious amounts of bacteria in bentgrass expressing symptoms of yellowing, etiolation, and gradual thinning. We don't know if these bacteria are the cause of the problem or if they are a secondary invader. As a result, we don't know if this is an actual disease or not. For more information, see our recent blog post.

A severe case of yellow spot on creeping bentgrass.

'Bacterial wilt' is caused by Xanthomonas translucens and is primarily a problem on Poa annua but also occurred on 'Toronto' creeping bentgrass back in the 1980s. Bacterial wilt causes rapid wilting and dieback of infected plants. Chlorosis, etiolation, and slow thinning of the turf doesn't fit the description of this disease. Therefore, what we are seeing now is NOT bacterial wilt.

We've had countless calls and samples over the last week from superintendents who fear they have bacterial wilt because they are seeing chlorotic or yellow turf. It's important to realize that many things can cause turf to turn yellow, and that if you aren't seeing the etiolation and gradual thinning then you probably don't have this suspected bacterial problem. For more information about some of the most common reasons for yellowing turf, please refer to this post on turfdiseases.org.

Several of the samples that came into our clinic this week turned out to be yellow spot. This disease causes chlorotic spots and patches on creeping bentgrass putting greens, but does not cause an abnormal growth habit and we've never seen it lead to thinning of the turf.

Yellow spot symptoms are especially prevalent during dry and hot weather. That certainly fits the conditions we're experiencing in North Carolina right now. For more information about yellow spot, please refer to this Golf Course Management article from the November 2006 issue.

Avid Receives 24(c) Label for Nematode Control in NC

Golf course superintendents in North Carolina have a new option for nematode control on putting greens.

Avid (abamectin) has been granted a 24(c) Special Local Need label for control of sting and ring nematodes on golf course putting greens. The supplemental label can be downloaded here. It is important to emphasize that this 24(c) label applies only to the Avid brand, is only valid in North Carolina, and only allows for application to golf course putting greens.

The application rate is 57 ounces per acre, with a recommended 3 to 4 applications on a 14 to 21 day interval. Tank-mixing with a non-ionic surfactant is recommended to improve penetration into the root zone, and applications should be watered-in immediately with 0.1" of irrigation.

Suspected Bacterial Disease of Creeping Bentgrass

Over the last two weeks, the Turf Diagnostics Lab at NC State received several samples of a suspected bacterial disease on bentgrass putting greens. All of the affected golf courses have been in the Piedmont region, from Raleigh to Greensboro to Charlotte.



Most locations are reporting yellowing and etiolation of the bentgrass followed by a slow thinning. The symptoms are relatively mild in these locations. Two courses experienced a more rapid and widespread decline. In all cases, the symptoms are limited to areas that were severely damaged last year by heat stress or other diseases.

We are working to isolate and identify the bacteria associated with these samples. Since there are bacteria in almost every turf sample we receive, we need to determine if the bacteria are pathogenic before we can be sure that they are the cause of the problem.

In the meantime, golf course superintendents who are seeing these symptoms are advised to avoid abrasive practices like aerification, verticutting, and topdressing. If the symptoms are localized to cleanup passes or certain greens, then dedicate a mower to those areas or wash the mower thoroughly and spray it with a 10% bleach solution before moving to other greens. Mowing affected areas last after the dew has dried or spraying with a hydrogen peroxide solution before mowing may also help to minimize the spread of bacteria.

In addition, anything that can be done to minimize stress on the turf is advised; for example raising mowing heights, switching to solid rollers, or skipping mowings on affected areas.

We are investing all of our effort and resources into determining the cause of this problem and developing a practical solution. We have initiated trials at 4 golf courses to evaluate practices that may help to control it. Be sure to follow our blog or sign up for email alerts to receive regular updates:

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