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.
Herbicide Resistance Info
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.