Can the coarse-droplet nozzles required for use in the auxin-tolerant cropping systems be used for the delivery of peanut weed control programs? Or more simply, will growers have to switch nozzles every time they go from an auxin-tolerant cotton or soybean field into a peanut field?   

That could be both time and cost prohibitive to many farmers.  

In numerous research trials, the weed control performance of the dicamba and 2,4-D systems has been good.  Both 2,4-D and dicamba tolerant crops should be a welcome addition to the weed control toolbox of many growers. Interestingly, dicamba-tolerant cotton varieties were planted on 43% of the acres in the Southeast in 2016.

Perhaps the biggest concern with these new technologies is the potential off-target movement (drift and volatility) of herbicides to sensitive crops.  Consequently, future auxin labels for use in tolerant crops will have specific recommendations for many application parameters including wind speed, tractor speed, GPA, boom height and nozzle type.

Since all of the required nozzles for these new auxin technologies will produce coarser (i.e. larger) droplets when compared to the traditional flat fan nozzle, weed scientists around the country have been frantically testing their effectiveness.

With that thought in mind and the assistance of an able-bodied, Georgia-grown graduate student, field trials were conducted in 2015 and 2016 to evaluate the effects of nozzle type on peanut weed control systems.  Results of this 2-year study are presented in Table 1.  When averaged over 4 complete peanut weed control programs, nozzle type had no effect on peanut injury, Palmer amaranth control, and peanut yield.  However, annual grass control was reduced by 5% when TTI02 nozzles were used.  A reduction in grass control with larger droplet nozzles has also been observed by other researchers.

Of the 3 nozzles evaluated in these tests, the TTI nozzle produced the coarsest (largest) droplet (VMD₅₀ = 524 microns).  VMD₅₀ values for the DG and AIXR nozzles were around 332 and 402 microns, respectively.  You may recall that I addressed droplet size in a previous edition of this column (February 22, 2016).

Although these results are promising and suggest that peanut growers should be able to use the coarser droplet nozzles, I would encourage all to proceed with caution.  Hopefully in 2017, I will be able to test these nozzles in a commercial sprayer operating at faster ground speeds to confirm the results from these small-plot tests.           

It will be interesting to see what develops over the next few months in regards to the labeling of herbicides for use on auxin-tolerant crops.  One thing for certain is that growers will have to change nozzles.  If a peanut grower decides to use a coarser droplet nozzle, an additional herbicide application might be needed if grasses are a problem.  As always, good weed hunting!