There can be a number of reasons why fungicides might not perform as well as we expect them to. I was recently asked if we are seeing failures with Miravis plus Elatus. There are cases in the southeastern U.S. where protection from leaf spot has decreased when this fungicide program is used. There is work going on to characterize the reason why this has occurred. Is the decrease in sensitivity of the pathogen to Miravis due to resistance or something else? This is being debated in detail by pathologists across the U.S. working in peanuts.
I'm a weed scientist by training who works in other disciplines, primarily agronomy, but I have stretched into pathology, entomology and nematology when needed. But I only go an inch or so deep on these last three disciplines. When it comes to mechanisms of resistance that may explain what we see in the field with resistance and product performance, there can be variation in terminology and how systems work when comparing pest disciplines. When I point out something in these posts or in other places, I’m checking myself with the experts we have at NCSU and other states to make sure I‘m as accurate as I can be in the moment.
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One thing we have noticed with Miravis and Elatus (and it would be the same for chlorothalonil) is that any pathogen activity that began before the Miravis/Elatus (or other stem rot fungicide mixed with Miravis) spray is going to continue developing after the Miravis/Elatus spray. There is no curative activity. In a case like this, you can say Miravis/Elatus let you down, but that gets back to knowledge and expectation. The weak link could be the fungicide or fungicides applied prior to Miravis/Elatus or gaps in sprays. We have had gaps in our 14-day schedules. And we always have some spray programs that start on the late side and allow some pathogen activity. Anything that allows the pathogen to be active is going to translate into more disease after a Miravis/Elatus spray. Miravis/Elatus may be working well on what begins in its window of protection, but it can’t cure what is already going.
So, there are several take-home messages:
- If Miravis/Elatus is used, the previous fungicide program needs to have done a good job of not letting the pathogen get going and disease developing.
- If you are confident that the previous fungicide program did a good job of protection, a decrease in sensitivity of the pathogen to Miravis might indeed be present. If that is the case, you may have experienced a three-week gap in protection.
- If you are seeing some disease now, regardless of what was going on in points one and two above, you need to focus on protecting as many leaves as possible. We are putting a lot of pressure on Provost. It is one of the fungicides that offers some curative action. There could be others too. We have about four weeks remaining to protect peanuts from leaf spot to avoid canopy defoliation. Don’t be complacent. Be diligent with sprays as you move into September. Reach out to local pathologists for specifics. I’m here to help too, but reach out to those who know more details. I’ll be doing the same.
