Peanut Disease Update (Kemerait)

Dr. Bob Kemerait issued the following disease update. I just went through the weather station data and we are recording from 10.3″ to 14.1″ of rain in the last 30 days here in the Suwannee Valley. Some farmers have reported higher amounts at their farms.

Monsoons in June bring High Risk in July

Dr. Bob Kemerait, UGA Plant Pathology

Much of the Coastal Plain of Georgia and the southeastern United States has been pounded by relentless storms and rains in June 2013.  As one former agent in east Georgia described, “I have had 13 inches of rain at my house this month and that is a desert compared to the rest of the county.”  It is estimated that some areas in Jefferson County, GA have had upwards of 25 inches of rain this month.

Such rainfall, like the monsoons of Southeast Asia, creates tremendous headaches for our peanut growers.  Such torrential downpours do the following:

1.  Creates prolonged periods of leaf wetness needed by fungal pathogens for spore germination, growth, infection, sporulation and spore dispersal.

2.  Spread the spores over small and large distances in rain-splash and blowing rain.

3.  Creates problems where rainfall occurs before there is sufficient time for the recently applied fungicide to dry before being washed from the plant.

4.  Creates conditions where growers cannot get into the field to make fungicide applications until long after such a protective spray was needed.

Below are situations that have been reported to me and advice that I offered.

1.   “I have a grower whose peanuts are 50 days old and he has not been able to make the first fungicide application.  What should I tell him?”

1A.  The obvious problem is that the grower is long-overdue for early protection of the peanut crop and some infection (leaf spot, white mold, and Rhizoctonia limb rot) may have already occurred.  It is imperative to protect the crop as quickly as possible.  I believe that the best protection at this point for leaf spot is either Headline (9 fl oz/A) tank mixed with something like tebuconazole (7.2 fl oz/A) to get a jump on white mold control or to consider the benefits of a program where Proline/Provost program is used for excellent leaf spot and soilborne control.  Within two weeks of the Headline/tebuconazole application, the grower should come back into the field with an aggressive program for management of leaf spot and soilborne diseases.  The best choice of fungicide will depend on the predominant soilborne disease- white mold or Rhizoctonia limb rot.  While our soilborne fungicides are effective for both, some are “excellent” for white mold while others are “excellent” for Rhizoctonia limb rot.

2.  “What about Peanut Rx, Bob?  My grower has a field at low risk.  How does this weather change his plan?”

2A.  Great question! The weather is so severe this season that even low-risk fields may have increased risk to disease.  For this reason, all growers should consider disease to be a serious problem this season, regardless of risk defined by Peanut Rx.  This does not mean that every grower needs to spray his field on a 7-spray program; however it does mean that all fungicide programs should be more conservative in 2013 because of the tremendous impact the weather will have on disease.

3.  “Bob, what diseases are being reported in the field now?”

3A.  Although conditions are extremely favorable, we have only had Aspergillus crown rot (associated with farmer-saved-seed) and white mold (research plots in Attapulgus) reported.  Still, growers need to know that leaf spot, white mold, Rhizoctonia limb rot, and even Cylindrocladium black rot are likely to be problematic this year.

4.  “Bob, you have an opinion about everything… What are your thoughts about choices of fungicides in 2013?”

4A.  Yes, yes I always have an opinion; however they are based upon our data.  First, it is important to consider use of fungicides with systemic activity/curative activity this year for leaf spot control.  With the weather this summer, there is a good chance that some leaf spot is already present in a field before a fungicide program can be established.  All of our fungicide programs, except for chlorothalonil or dodine (Elast), will offer some measure of systemic activity and can be deployed effectively.   Our very best leaf spot programs include use of Headline or Provost.  Fontelis is strong on leaf spot and there is now the opportunity to mix Abound (18.5 fl oz/A) with Alto (metconazole, 5.5 fl oz/A) for increased control of leaf spot.

All of our soilborne programs are effective for use in our peanut fields; however Abound gets special attention for Rhizoctonia limb rot; Provost for CBR, and Artisan, Convoy and Fontelis for white mold.  Tebuconazole is a great value for the price; however it is not the best soilborne fungicide our growers can choose.  Diseases will be of significant concern this season and growers are encouraged to invest in the fungicide program their crop needs for optimal yields.

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