Weed Science Update - February 26 (Prostko)

     Over the last several days, a few interesting things have crossed my desk.  Thought you might want to see them as well.  Figure 1 is a picture of a weed from a plantation in SW Georgia (https://plants.usda.gov/core/profile?symbol=pagl17).  Numerous yellow flowered plants are blooming at this time of year so be careful when identifying.  Figure 2 is a picture of Palmer amaranth that has already emerged somewhere in SE Georgia.  Seems too early to me but also serves as a reminder that growers should consider a residual herbicide if planting will be delayed after ground preparation.  Figure 3 is a picture of volunteer Xtend (dicamba) soybeans in winter wheat.  Not an easy weed to control since they are resistant to dicamba.  Depending upon wheat stage of growth, best bet for control might be Harmony Extra + MCPA?  Importantly, these soybeans were not STS/SR.  Figure 4 illustrates how glyphosate rate and timing are important for the control of annual ryegrass.  Assuming resistance is not an issue, I would suggest at least 48 ozs/A of glyphosate are needed.

Figure 1.  Butterweed (Packera glabella).

Figure 2.  Palmer amaranth emergence in February??

Figure 3.  Volunteer Xtend (dicamba) soybeans in wheat? 

Figure 4.  Rate and timing of glyphosate for annual ryegrass control.

Bermudagrass Burndowns (Prostko)

     During the last few weeks, I have received a few inquiries about controlling bermudagrass prior to planting various row crops.  An established stand of bermudagrass can be very difficult to manage.  When dealing with bermudagrass burndowns, glyphosate rate and time of application are crucial.  Here are a few points to consider:

1) When applying glyphosate in the spring, when is the best time of application?  Generally, later applications are more effective after the bermudagrass has greened up and is actively growing (Figure 1).

  
2) Can bermudagrass be effectively controlled with 1 application of glyphosate?  What rate of glyphosate should be used?  In previous UGA research, the most effective control of bermudagrass occurred when 3 applications of glyphosate @ 2 lb ai/A were applied (Figure 2).  Obviously, this program would have to be implemented the year before planting a spring row crop.  I hope you notice that a single application of 4 lb ai/A of glyphosate applied in May was not very effective (38% control).

3) Growers who are relying on spring applications of glyphosate only will almost certainly have to follow up in-crop with 1 or 2 applications of a postemergence grass herbicide, such as Select or Poast (only in labeled broadleaf crops), or glyphosate (only in labeled GR-crops).  Consequently, those extra herbicide costs should be included in their budget plans.  Additionally, it might take a few years of fighting before optimum bermudagrass control will be obtained.