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Sicklepod becoming difficult in peanuts, but not a resistance issue yet

Eric Prostko/UGA Extension sickle-pod-prostko-sefp-june.jpg
A Sumter County, Ga., sicklepod population treated with Cadre @ 4 oz/A + COC @ 1% v/v in the greenhouse at 21 days after treatment in 2017 (treated – left, untreated – right).
Over the last few years, I have observed with my own eyes and heard complaints with my own ears about the reduction in sicklepod control that has been occurring in some peanut fields.

Over the last few years, I have observed with my own eyes and heard complaints with my own ears about the reduction in sicklepod control that has been occurring in some peanut fields. 

The potential causes of this problem have been speculated to be anything from herbicide resistance to alien intervention.  Although I am a believer in UFOs, I seriously doubt that visitors from other planets have had anything to do with this particular problem.

My PhD graduate student O.W. Carter and I have been conducting greenhouse experiments over the last two years to determine if sicklepod has developed resistance to Cadre (imazapic).  At this point in time, O.W. and I have screened about 20-plus Georgia sicklepod populations and have yet to find one that is even remotely resistant to Cadre (imazapic).  We still have a few more populations to test though?  So if herbicide resistance and extraterrestrials are not the cause of this problem, what is?

Overall peanut plant health plays a vital role in sicklepod control.  An optimum stand of well-growing goobers can be very competitive with sicklepod.  Previous research has shown that if a peanut field can be kept free of sicklepod for eight weeks after planting, the peanut canopy can suppress 95 percent of the sicklepod emergence for the remainder of the growing season.  Unfortunately, much can happen during the 135-150 day peanut growing period that can negatively influence a peanut plant’s competitive abilities, even when grown under irrigation and/or in twin rows.

Another potential cause of this problem has to do with herbicides.  In peanut, there really are no herbicides that provide adequate soil residual control of sicklepod.  Popular peanut residual herbicides such as Dual Magnum, Prowl, Sonalan, Strongarm, Valor and Warrant are not very helpful when sicklepod is a problem.  Consequently, sicklepod can germinate and emerge throughout the year.  

Additionally, the expectations for postemergence herbicides such as Cadre and 2,4-DB may be unrealistically high since long-term sicklepod control averages for these herbicide are approximately 86 percent (Cadre) and 70 percent (2,4-DB).  Sicklepod control with Cadre can improve to about 94 percent when it follows an earlier “cracking” application of Gramoxone (paraquat) + Basagran (bentazon) or Storm (bentazon + acifluorfen).  As a last resort, don’t forget that paraquat applied in a non-selective applicator (NSA) can be very effective for late-season sicklepod management.

When a postemergence herbicide fails to provide satisfactory weed control, it is usually because of the environmental conditions (hot and dry) and weed size (too big) that exist at the time of application.  Growers cannot do much about the environment but they can try to be timelier with their postemergence herbicide applications.  That is easy for me to say but hard for many to do in reality. 

I am also of the opinion, although I have yet to prove it scientifically, that faster application speeds could also be partially to blame.  This year (2017) marks my 20th peanut crop.  Many peanut growers are not applying herbicides the same way today as they did back in 1997 or 2007 (slower speeds and smaller spray rigs). I am still not 100 percent convinced that bigger is always better when it comes to weed management?

Now there is no great answer for this sicklepain problem that is occurring.  All I can suggest today is that you try to grow the most vigorous peanut crop as possible, be timelier with your postemergence herbicide applications, and use paraquat in a NSA if needed. 

As always, good weed hunting!

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