Comments From Dan Anco Clemson Disease Control Peanut Notes No. 94 2019

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Comments on Disease Management in Peanuts
June 14, 2019
Daniel J Anco
Dr. Anco is located in South Carolina. While management of disease and other pests can vary across the Virginia-Carolina region, many of Dr. Anco’s comments would apply across the region but more specifically southeastern North Carolina.
Fields planted between April 30 and May 10 are right at 45 and 35 days. Along with herbicides going out, fungicide programs are starting or are coming up soon. Bravo is the economical standard at this time when field rotation history and cultivar resistance help moderate pressure. If wet weather delays entry for about two days past when we would like to get a spray in, use or addition of a systemic product to the tank can help recover some protection.
We are still a couple weeks off before the 60-day spray where Miravis will be going out in places, so I won’t spend too much time on it here except to say that if we are considering an extended interval following its application, we still need to keep the weather in mind for washing a white mold product into the soil. Irrigated Virginia type peanuts have a good match with a Miravis program, both from the white mold resistance and the irrigation side for yield potential and washing fungicide into the soil. Dryland runners are a little more variable, since most are more susceptible to white mold, though Georgia 12Y has great resistance and FloRun 331, TifNV-High O/L, AU-NPL 17, Georgia 14N have good resistance but are still limited in acreage. This makes the soil delivery of these products even more important considering the potential for hot and dry weather to ramp up the disease.
The recent rains have no doubt helped, but keep eyes open for pests. Beet armyworms and bud worms have been reported in some peanuts earlier this week, which is about a month ahead of schedule.
Fungicide Sensitivity
For fungicides both now and later in the season for leaf spot, some products have been appearing to have reduced performance in recent years, particularly strobilurins (Abound, Headline…) applied alone. One of our projects supported by the South Carolina Peanut Board is looking into possible fungicide resistance in the state. The good news is that the old standby multi-site chlorothalonil (Bravo) continues to show robust performance. From the 9 counties we sampled against 5 active ingredients, late leaf spot was typically always less sensitive to azoxystrobin than for chlorothalonil. In Dorchester County, however, thiophanate methyl (Topsin) showed less activity than azoxystrobin, with different levels of activity in other counties. We did see some prothioconazole activity somewhat slipping in places, including Hampton, Marlboro, and Calhoun Counties, and a few fields from Barnwell County as well. Benzovindiflupyr (one of the actives in Elatus) is still showing overall activity, but samples from Darlington County were less susceptible than others.
The ‘disclaimer’ for this if you will, is that we intentionally tried to detect possible insensitivity from a mix of different lesions. This is similar to not having any product rotation on a highly susceptible variety under favorable conditions, and seeing disease develop. Control in the field may be different, but always good to have a possible heads up.
Not all doom and gloom by any means, always good news in the mix. I think we can still incorporate different products in an overall effective program. A couple of things to keep in mind, some of these are familiar. Cultivar resistance and 3+ years of field rotation goes a long way in mellowing pressure. The dry start to the year certainly helped there too. For application, Abound and Topsin should be tank mixed with another product (Bravo) and not applied alone. Overall, Abound is more helpful against Rhizoctonia where that is a concern than it is on late leaf spot. In counties showing less sensitivity, application of products with prothioconazole (Provost, Proline) on susceptible varieties (Virginia types, TR 511) or in fields with histories of disease control challenges should be rotated if used with different modes of action and/or tank mixed. Microthiol Disperss has contributed great benefit to prothioconazole in our tests, and although the 5 lb/A rate can be bulky to deal with, it is easy on the wallet.
If you would like to test leaves from fields this year, your Extension agent or consultant can help and we can take a look. We are working on speeding it up, but currently, it takes a few weeks for results, which is too slow for how fast decisions need to be made sometimes, but still a way to get information.
Dan Anco
Extension Peanut Specialist and Assistant Professor
Department of Plant and Environmental Sciences
Clemson University – Edisto Research and Education Center
64 Research Road
Blackville, SC 29817
803-284-3343 x261 office
630-207-4926 cell
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