Grass Herbicides for Pre-Plant Burndown?? (Culpepper and Prostko)
Thinking about using a grass herbicide such as Select Max (clethodim) for pre-plant burndown? Have you seen any data suggesting this is a wise decision?
Interestingly, there is a lot of buzz about using grass herbicides to burndown small grain cover crops and annual ryegrass because of the glyphosate price/shortage issues. Most of the conversations also include tank-mixing the grass herbicide with either 2,4-D or dicamba and applying as a March/April burndown.
Prior to making the effort and spending a significant amount of money, it might be wise to review the grass herbicide label itself for the level of control the product potentially offers. Additionally, you may find value in the data we generated in 2021 (Figure 1). A couple of important clarification notes regarding this research are as follows: 1) the application was made on February 28 (2021) when conditions were cooler; 2) we did not tank-mix with dicamba or 2,4-D, which could negatively influence grass control (i.e. antagonism); and 3) this is data from only one location.
When considering your burndown treatment for 2022, a significant amount of research suggests that the value of glyphosate may be at its maximum for the pre-plant burndown application if grasses are present in the field. Thus, we would encourage staying with the burndown program that you know is successful if anyway feasible. Planting into weed-free fields, with the potential lack of some postemergence herbicides this year, will be extremely important.
Once grassy weeds, as well as other broadleaf weeds are mature, Gramoxone (paraquat) + diuron + COC (cotton) or Gramoxone + Valor + 2,4-D amine + COC (peanut) are fantastic options (small grains must have seed heads). It appears, at least currently, that most of our winter weeds are maturing at a faster rate than in the past so these treatments may be very timely options.
Tillage is also a very effective option as you well know, just be cognizant implementing steps to avoid soil erosion.
Another possible negative. If Select Max is used prior to planting field corn, the plant-back restriction would be 30 days. The rate needed for burndown control (marginal) is much higher than the rate needed for volunteer corn control thus warrants a longer restriction.