Georgia Soybeans: 5 Considerations for Late Season Weeds

It has been a while since my last blog.  In the last 60 days, I was out of commission for at least 27 days for various reasons (vacation time, 3 professional meetings, and 2 college moves).   However, the telephone calls kept rolling in!  Here are a few things to consider based upon recent calls:

1. Glyphosate will not adequately control sicklepod plants that have emerged thru the top of a soybean canopy.  However, glyphosate might have some effect on seed rain depending upon the sicklepod stage of growth at application and how much of the plant actually gets treated (Figure 1).  However, I would not expect as much seed reduction as depicted in this graph if only a few inches of the sicklepod plant actually gets treated with glyphosate.

2. Growers who have planted ultra-late soybeans need to be more conscious of herbicide crop rotation restrictions.  For example, Reflex, Prefix, or Warrant Ultra all have a field corn rotation restriction of 10 months (yes, this is real!!).  Thus, these herbicides should be avoided if field corn will be planted early next spring.  POST soybean herbicides with minimal crop rotation restrictions include Liberty, Cobra, or Ultra Blazer.

3. At this time of year, there are NO miracle cures or magical silver bullets for escaped morninglory, Texas panicum, or sicklepod in any crop.  Growers will need to rely on harvest aids or non-selective applicators when appropriate and/or labeled.  What’s the best strategy for controlling a 12-24″ weed?  Treating it when its 3″ tall!!!!!!!!!!!!!!  Sometimes a difficult but necessary pill to swallow.

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4. Growers need to stay vigilant in their post-harvest (corn) weed control efforts to minimize weed seed-rain back into production fields.  It would only take a few escaped, seed-producing plants to mess up multiple years of good weed control.  Please refer to pages 74 and 87 of the 2016 UGA Pest Control Handbook for more information about post-harvest weed control strategies.

5. As a reminder, I would be more than happy to spend some time in any county at this time of year at your request!

Figure 1. Late-season response of sicklepod to glyphosate @ 0.75 ai ae/A as influenced by application timing.