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Is Emerald a Poor Curative for Dollar Spot?


Over the years, I've heard a number of people say that Emerald is a slow or poor fungicide for curative control of dollar spot. I must confess that I've never understood what everyone is talking about.

Given that boscalid, the active ingredient in Emerald, controls fungi by depleting their energy reserves, it makes sense that it might be a little slow to work on a curative basis. However, in reality, I've always been impressed with it's activity on both a preventive and curative basis.

Let's look at a couple of examples. In this first curative dollar spot control study, we had an average of 40 to 45 dollar spot infection centers in each plot before initiation of treatments. That's not a huge amount of dollar spot on a 20 square foot plot, but certainly enough to warrant a curative fungicide application in a golf course setting.

On July 20, just 5 days after applying the low rate of Emerald, we reduced the number of infection centers down to 2 per plot, whereas the number in untreated plots held constant. So, the low rate of Emerald reduced dollar spot incidence by 95% in 5 days. I'd consider that to be pretty good curative activity! If you're expecting more than this out of a curative application, then you are probably expecting too much.

Looking at some older data, in 2006 we evaluated Emerald, Daconil + Emerald, and Daconil + Banner for curative dollar spot control. In this case, the dollar spot pressure was much more intense, with 150 to 200 dollar spot infection centers per plot before the initiation of treatments. After the first application on 19 Jun, dollar spot incidence declined in all of the treatments at a similar rate and none of the treatments were disease free until three weeks later on 10 Jul. And this is even though dollar spot disease pressure was much lower during late June and early July, as evidenced by the decline in the amount of disease in untreated plots.

Curative control of any disease is more dependent on the level of disease pressure, the amount of turf injury present, and the growth rate of the turf after the application. Which fungicide is applied probably isn't that important in most cases. In order for the disease symptoms to go away, the turf has to grow out of the symptoms and spread into the damaged areas. This, of course, takes time. There aren't any fungicides that will make dollar spot go away over night.

For a lot of reasons, we don't recommend controlling dollar spot on a curative basis. Perhaps the most important reason is that curative applications increase the risk for fungicide resistance to develop. If you find yourself in a situation where you need to make a curative application for dollar spot control, be sure that you are tank-mixing with chlorothalonil to reduce the potential for resistance to develop. This is especially important for products with a high resistance risk like Emerald.

6 Responses to “Is Emerald a Poor Curative for Dollar Spot?”

D Smith said...

Great comments Lane! I have been wondering the same thing myself as we see similar results on putting greens here in Oklahoma treated with Emerald. Thanks for posting this.

Damon

Jim said...

Lane thanks for saying this. I have heard the same thing and I think some are impatient when it comes to Emerald. We have observed that iprodione mixed with chlorothalonil provides a good initial knockdown, even quicker than Emerald. Yet within a week or so, Emerald was out performing all treatments in our study. Our plots were 30 square feet and during this trial dollar spot exploded over a weekend and when we started applications we had around 300 spots.

So again thanks for clearing this up. Use preventative applications for dollar spot!

Jeffrey Johnson said...

So when is the proper time to make the preventative application of Emerald? I've been told to make an early spring application in Minnesota, say around the middle of May? Your thoughts?

Jim said...

Jeff- Lane can chime in too, but I do like Emerald early in the season (Mid-Mayish). I also like Emerald during the first fall application because it seems to get people through the fall lingering of dollar spot.

Anonymous said...

Are we talking about true early season dollar spot apps? For instance, dollar spot often first shows up in the NE around mid/late May but early season apps start in early/mid April (after the 2nd true mowing). If so, Kaminksi's work with early season apps for dollar spot suggests that as long as the fungicide works for suppression at your course, the overall efficacy (Emerald is often better than other dollar spot fungicides) isn't as crucial. For example, if Curalan and Emerald both provide dollar spot control, the less expensive fungicide makes more sense. Kaminski can shed more light on the subject obviously but I think I referenced his work accurately.

In my travels Emerald has been a great material for dollar spot prevention and I do see value in timing apps for early summer and especially early fall when we tend to see more damaging/pitting dollar spot.

Adam Moeller

Jim said...

Adam,

In our early-season trials in the Midwest, we have not observed suppression with early-season applications of vincozolin or iprodione. Our early-season applications are the first of May or middle May, so we are little bit behind those in the Northeast.

I do agree that Emerald is ideally placed during early fall.

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