Field Corn Weed Control Update (Prostko)

Field corn weed control does not have to be difficult.  Just about any of the herbicide programs that growers are using in Georgia do a good job of controlling most weeds, especially Palmer amaranth, when applied to small plants (<3" tall). Want some proof? Check out the following pictures from my field corn plots that I rated earlier today (click on pictures to make them larger).  Just so you know, these herbicide treatments were applied 17 days after planting with a CO2-powered backpack sprayer calibrated to deliver 15 GPA at 3.5 MPH using AIXR 11002 nozzles.

The most troublesome weed in Georgia field corn, in my opinion, is annual morningglory.  Field corn growers who struggle with morningglory should seriously consider a post-directed/lay-by application of Evik (ametryn) sometime after their initial POST treatment was applied.  Check out page 70 of the 2017 UGA Pest Control Handbook for more information about Evik.  The minimum corn height for post-directed applications of Evik is 12".  If Evik is tank-mixed with glyphosate, post-directed applications can be applied up until 48" tall corn (RR2 hybrids).

Glyphosate/Atrazine/Adjuvants in Field Corn (Prostko)

A common question this week from field corn growers is "Do I need to add a crop oil concentrate (COC) when applying glyphosate + atrazine?"  For you Roundup babies out there, Atrazine + Prowl + COC was one of the most common and effective field corn herbicide treatments in Georgia before the introduction of RR-crops.  Thus, it is tough for seasoned field corn growers to consider not using a COC.  With that said, there is no need to use a COC when a fully "loaded" formulation of glyphosate is used.  Fully "loaded" glyphosate formulations already contain enough adjuvants.  In fact, COC's have been known to cause antagonism when mixed with glyphosate.  

Fully "loaded" glyphosate formulations include the following:  Abundit, Barbarian Max, Buccaneer Plus, Cornerstone 5 Plus, Credit/41Extra, Credit Xtreme, Duramax, Durango DMA, Gly-Fos Xtra, Glysort Plus, Gly Gold Extra, Gly Star Plus, Helosate Plus, Helosate 70, Mad Dog Plus, Makaze, Roundup PowerMax, Roundup WeatherMax, Showdown, Touchdown CT, Touchdown IQ, Touchdown Total.

In my own research program, I have not been using additional adjuvants with Roundup + Atrazine for a very long time (Figure 1).

If a grower uses a glyphosate formulation that is not loaded at all or is partially loaded, then he/she should consider adding a non-ionic surfactant (NIS) @ 0.25% v/v or 1 qt/100 gal.

Figure 1. A common field corn weed control program.  No adjuvants were used with the POST treatment of Roundup PowerMax + Atrazine.  FYI, this entire herbicide program costs approximately $16.50/A (excluding application costs).