Questions About Leaf Spot Control Peanut Notes No. 104 2018
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Here are some questions we’ve gotten about different leaf spot scenarios that have developed over the past couple of weeks:
Question 1 – A spray is due or overdue. It’s too wet to get equipment into the field and more rain is forecast. Should the grower consider an aerial spray?
Answer: Yes. Aerial fungicide application may not be ideal, but as long as favorable conditions continue, it is important to maintain protection. Follow up in 10 days with a ground application.
Question 2 – A spray is overdue and the grower is ready to make an application. What fungicide would you recommend?
Answer: The choice of products will depend somewhat on what has been applied already, but I would recommend a product that will penetrate the leaves and/or move systemically. In this scenario, tebuconazole (“Folicur”) + Bravo is NOT a good choice because tebuconazole probably will not provide any leaf spot control and Bravo is strictly a surface protectant. If no stem rot fungicide has been applied to date, consider using 10.7 oz/A Provost. If a stem rot fungicide such as Provost, tebuconazole, or Elatus has already been used, the grower may want to switch to 8 oz/A Priaxor or 3.4 oz/A Miravis.
There are many other possibilities that could work for a given situation. However, fungicide selection has become very difficult due to unexpectedly poor control provided by some products in some areas. Don’t use a product that has under-performed for you in the past. If at all in doubt about efficacy, add 1 to 1.5 pt/A chlorothalonil to the fungicide mixture. Scout carefully and be prepared to shorten intervals to 10 days if needed.
Question 3 – The grower went almost 28 days without a spray and now has an outbreak of late leaf spot. What should the grower do?
Answer: This is very bad news. While our conditions have been very challenging, we should not be seeing significant late leaf spot this early. See the answer to Question 2 for fungicide options. The main differences to the answer for question 2 above and this one are 1) the grower should definitely plan to spray right away and then again in 7 to 10 days; 2) the grower should avoid products already used in case the population in the field is resistant to one of those products; 3) the grower should add at least 1 pt/A Bravo to whatever product is selected to reduce the risk of fungicide resistance.
Question 4 – Can a grower expect 28 days of leaf spot control from Miravis?
Answer: We have applied Miravis at 21 – 28 day intervals in our trials. We see slightly more spots with longer intervals, but this has not impacted defoliation or yield. However, our experience with this product is still limited so a cautious approach is wise. Use extended intervals in fields with good rotations and where excellent leaf spot control has been maintained to date. Remember that protection against stem rot is still needed: mix Miravis with a good stem rot fungicide if you plan to wait 28 days before the next fungicide application. Applying Miravis in early August and waiting 28 days would make a spray due in early September. Growers should plan to apply Bravo or other broad-spectrum fungicide at that time to carry protection through harvest, especially given the challenging weather we have had this summer, and the possibility that these conditions may persist in the fall.
Question 5 (not asked yet) – Should I be worried about Sclerotinia blight?
Answer: Yes! We’ve had continuously favorable weather for the past 3 – 4 weeks. Scout carefully and treat with 1.5 pt/A Omega preventively or at the first sign of disease.