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2012 Peanut Disease Management

                                                                                                                                                                 

Peanut Pointers February 2012
Bob Kemerait, University of Georgia
Extension Plant Pathologist

 Though we are 2 ½ months away from planting peanuts, there are a number of important points for growers to consider now with regards to management of diseases and nematodes affecting the crop.   These points include:

  1. 1.       Our winter weather.  With the exception of a few cold snaps, the winter of 2011-2012 has been both mild and dry.  Although it is impossible to say exactly how the warm temperatures will affect diseases and nematodes in the 2012 peanut crop, a few important observations should be made.  First, the weather in 2011-2012 has been very different from the winters of 2009-2010 and 2010-2011.  The impact of the weather this winter on thrips (the insects that vector tomato spotted wilt virus) is uncertain; however any affect that increases the thrips population or results in earlier flushes of thrips could have an impact on the level of spotted with this season.  Second, a warm weather could make problems with nematodes (on peanut and other crops too) worse in 2012.  Warmer soils may mean that the root-knot nematodes become active earlier in the season; it may also mean that weed hosts are available earlier in the year leading to an increase in population of the nematodes.  Regardless, I believe that a warmer winter with warmer soils could spell more significant damage from the nematodes on the peanut crop.  Third, warm soils could prompt an early-season outbreak of white mold, much like we have experienced in 2010 and 2011.  We typically recommend that growers begin their “white mold/soilborne” phase of a fungicide program approximately 60 days after planting.  However, when soils are unusually warm it is likely beneficial to the grower to begin his battle against white mold prior to 60 DAP.  Strategies for early-season white mold will be described below.  Fourth, the severity of Cylindrocladium black rot (CBR) in a given season is significantly influenced by the conditions at planting.  Should we experience a cooler and wetter spring, we can expect a more serious outbreak of CBR.  However, in warmer springs like those of 2010 and 2011, outbreaks of CBR have been few and far between.
  2. 2.      Fontelis (penthiopyrad) from DuPont.  Fontelis is a new fungicide for peanut growers that should receive a label from the EPA by the end of February and I fully expect it to be available for growers this season.  Recommendations from DuPont for use of Fontelis will likely include 3 applications during the season at a rate of 16 fl oz/A each.  Reasons for growers to consider use of Fontelis include, a) broad spectrum activity (white mold, Rhizoctonia limb rot, leaf spot, and suppression of CBR), b) good efficacy, based upon results from studies conducted at the University of Georgia and UGA Cooperative Extension, and c) the new mode of action that compliments fungicide resistance management efforts for strobilurin (Abound, Evito, Headline) and triazole (Provost, tebuconazole, Quash) fungicides.
  3. 3.      Management of peanut root-knot nematodes.  Whether or not our warm winter has any measurable effect on the damage from peanut root-knot nematodes in 2012, growers must still remain quite vigilant in order to protect their crop.  The sudden loss of Temik 15G in 2011 leaves a gaping hole in our means to manage nematodes on the peanut, as well as cotton and soybeans, crop.  Fortunately, growers can plant ‘Tifguard’; this peanut cultivar is virtually immune to the root-knot nematode and no nematicide is needed to protect it.  In fields planted to Tifguard, growers need only use a product to protect against thrips.  Some growers have expressed concern that a) the yield potential of Tifguard is not equal to some other cultivars, e.g. Georgia-06G, and b) Tifguard is reported y some to have “weak peg strength”.  In response, I offer that the yield potential of Tifguard without use of a nematicide in a field significantly infested with peanut root-knot nematodes is as good, or BETTER, than a non-resistant cultivar treated with a nematicide in the same field.  Second, after completion of several research studies, we cannot document any decrease in yield associates with an increase in loss of pods for Tifguard as compared to other popular cultivars.  Growers planting a variety OTHER than Tifguard in a field with damaging levels of peanut root-knot nematode must consider fumigating with Telone II (1,3-dichloropropene- 4.5 to 6 gal/A).  Telone II is an excellent nematicide; use of Telone II should be complimented with the use of another product, like Thimet or phorate, for control of thrips.  Agents should alert growers to the fact that supplies of Telone II will be limited again in 2012.  Also available to peanut growers in 2012 for the management of nematodes are Enclosure (iprodione from DevGen) and neem oil.  Research efforts continue on both products at the University of Georgia to assess their use and efficacy in the peanut crop for the management of nematodes.
  4. 4.      Early season white mold control.  Although “60 days after planting” remains our standard recommended date to begin the “white mold/soilborne” phase of our fungicide program on peanuts, there is no doubt that there are seasons, e.g., 2010 and 2011, when it is prudent to start the program earlier.  Work over the past two years has documented the opportunity to better manage a serious white mold problem by banding a FULL broadcast rate of Proline (5.7 fl oz/A) in a narrow band directly over the young peanut plants 2-5 weeks after planting.  The exact timing of the application for optimum white mold control may vary from season to season; e.g. in 2011 control of white mold improved as the time of application was delayed from 2 to 5 weeks after planting.  I would recommend that most growers consider the timing of an early-emergence application to be between 3 and 4 weeks after planting, recognizing that in some years even a little later can be beneficial.   In a study last season, Dr. Tim Brenneman achieved similar results in control using spray volumes of 40 gal/A and 10 gal/A.  Bayer CropScience recommends 20 gal/A for the early emergence application.  The early emergence application of Proline offers growers the opportunity for a good start on white mold control and, based upon a trial from 2011 in Colquitt County, Rhizoctonia limb rot control.  The use of Proline early in the season is followed by an effective white mold fungicide program at the appropriate time later in the season.  Growers looking for early season white mold control, but choosing not to use a Proline program, may consider the option to include tebuconazole in one or both of the first applications (30 and 45 days after planting) tank-mixed with chlorothalonil, Headline or other appropriate leaf spot material, so long as appropriate considerations are given to fungicide resistance management in the later soilborne fungicide program.
  5. 5.      Management of Cylindrocladium black rot (CBR).  For growers who anticipate problems in their field (or fields) from CBR, our basic management program remains as follows.  First, try not to plant peanuts following peanuts or soybeans.  Second, consider fumigation of the field with Vapam or metam sodium at 10 gal/A.  Third, if you do not use Vapam or metam sodium, we strongly advise that you apply Proline, 5.7 fl oz/A in-furrow at planting.  Note: Proline can be safely mixed with Rhizobium inoculants.  Fourth, consider planting the peanut cultivar Georgia Greener which has some documented resistance to CBR.  Fifth, follow up with a fungicide program that includes Abound, Headline, Provost, or other fungicide labeled for the suppression of CBR.

 

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