Early Preplant (EPP) Herbicide Applications...How Early Can They be Sprayed

By Dwight Lingenfelter

As the days warm and time gets closer to planting, certain residual herbicides can be applied prior to planting but timing is critical.

Historically, we have not recommended early preplant (EPP) herbicide application in our region with a couple of exceptions such as for marestail control. In general, residual herbicides applied more than two weeks ahead of planting almost always require additional weed control often in the form of a post application. With advancements in seed technologies with more herbicide resistant traits, there can be more opportunities to apply a residual burndown program two or more weeks ahead of planting with the idea of coming back with a well-timed post treatment. But keep in mind that by spraying a residual herbicide early, in some cases, “wastes” the utility of that residual product. Most of these products only provide about 4-5 weeks of residual weed control, so by spraying early there might only be about 2 weeks of residual once the crop is planted. Residual products tend to provide more weed control value when applied at planting. Another question raised relates to potential “tie-up” of the herbicide by a cover crop. Currently there is limited data about how cover crops, whether still alive or dead, affect the residual aspect of the herbicides. Furthermore, when tank mixing, certain products such as atrazine, can antagonize burndown herbicides like glyphosate and paraquat. However, for various reasons some may want to tank mix and spray both burndown and residuals in one pass. A number of herbicide labels specify in days what is allowed EPP. Herbicide rates may increase for EPP, so consult a current herbicide label for specific use directions. The table below provides some spring EPP application intervals for some common corn and soybean products.

Table 1. EPP application intervals for selected herbicides.

Regarding some of the popular PPO/Group 14 soybean herbicides (e.g., Valor products, Envive, Fierce, Trivence, Authority products, Sonic, Surveil, others), if using these in combination with Sharpen/Zidua Pro/Verdict/OpTill for control of marestail, there is a 14 day restriction before planting. So, if you tank mix Sharpen-containing products with another PPO/Group 14 residual herbicide you must wait 14 days to plant soybeans. Or if Sharpen is applied EPP in a burndown mix without the PPO residual product, then you must wait 2 weeks before applying the Group 14 residual herbicide at planting.