Questions of the Week? (Prostko)

Here a few questions that I received over the last few days or so.  Thought all might benefit?

1) How do I control ryegrass prior to planting peanuts if I suspect that I might have glyphosate resistance?

Select 2EC @ 8 oz/A or Select Max 0.97EC @ 16 oz/A (or generic equivalents) + 1% v/v COC  would be a good choice for this problem.  Remember that ryegrass stage of growth is important (Figure 1) and that temperatures below 50 F can significantly reduce control.  Higher rates of paraquat (3.5-4.0 pts of 2 lb ai/gal) can also be effective but 2 applications (10-14 days apart) may be needed.    

Figure 1.  Influence of clethodim timing on ryegrass control.  

2) What is the best nozzle to use for soil applied residual herbicides?

Generally, nozzle type is not as critical with soil applied residual herbicides when compared to postemergence herbicides.  For many years, I used a flat fan nozzle (11002DG) for all my weed control trials.  Recently, I started using an AIXR11002 nozzle as my standard.  I have also applied soil residuals with a TTI-02 nozzle.  I have not observed any reductions in the performance of residual herbicides when using these larger droplet nozzles.  Check out Figure 2 for a quick look at the coverage provided by these different nozzle types.  However, I would suggest that growers refer to the nozzle manufacturer for more specific information about the potential performance of nozzles with soil residual herbicides.

Figure 2.  Spray Coverage with Various Nozzle Tips

3)  What is ACURON herbicide?

Acuron, from Syngenta, is a mixture of s-metolachlor + atrazine + mesotrione + bycyclopyrone registered for use in field corn, seed corn, silage corn, sweet corn, and yellow popcorn.  Acuron can be applied preemergence or postemergence depending upon the type of corn.  I have tested Acuron for a number of years and it is a very good product.  It would be especially useful to growers who are dealing with glyphosate, atrazine, and/or ALS resistant weeds.  But in the absence of resistance, it's very difficult to for most higher priced new herbicides to beat the cost-effectiveness of a timely postemergence application of glyphosate + atrazine + Prowl tank-mixture in Georgia.   I do not have an exact figure but I have heard that Acuron is a bit pricey?

4) What is SHIELDEX herbicide?  

Shieldex, from Summit Agro USA, contains the active ingredient topyralate.  Shieldex is labeled for postemergence use in field corn, sweet corn, and popcorn.  Shieldex has the same mode of action as several other corn herbicides such as Callisto (mesotrione), Impact (topramezone), and Laudis (tembotrione).  All of these herbicides are HPPD inhibitors (WSSA MOA #27).  There are 2 good reasons why Georgia corn farmers need not worry about this herbicide:  1) it is not yet labeled in GA; and 2) I only have 1 field trial with this product (i.e. not enough data to make a solid recommendation).