Why Herbicide Timing is Important

Three main reasons why herbicide timing is important

1. Improved weed control and product efficacy

Herbicides are built and designed most often to control small actively growing weed species. As weed species are left to grow throughout the season, control is harder to achieve and often we are asking more of a product than what it was designed to do.  When we think about weed control and herbicide timing, the easiest time to control a weed is before it ever comes out of the ground (Figure 1).

Figure 1: Palmer amaranth control 77 days after the PRE application and 60 days after the POST (V3-V5 applications) of s-metolachlor + fomesafen

Residual herbicide applications are the best timing option to start weed control as they prevent, or delay weed emergence for an extended period.  This allows for weeds to be in a much more susceptible growth stage for maximizing postemergence product efficacy and maximizing weed control.  Herbicide timing can result in a 17% difference in product efficacy and weed control levels (Figure 1).

2. Maximize herbicide return on investment (ROI)

The critical weed free period (CWFP) for any crop is defined as the time during crop growth that it must remain weed free to mitigate yield loss from weed competition. This time varies from crop to crop, but often is within the first 6-8 weeks of growth. As mentioned in article (insert hyperlink) when weeds are not controlled during this period you are losing yield.  In addition to completive yield loss from weeds to crops, a grower’s financial investment in a herbicide application is also comprised if not applied at the appropriate time for maximum herbicide efficacy.

Depending on the crop in question herbicide applications can range from $56-170/acre.  This is a significant investment to a farming operation and by missing, delaying, or compromising suggested application timing for weed control we are decreasing the value of that investment.

3. Product stewardship and herbicide resistance management

By applying herbicides at the appropriate susceptible growth stage, we are preserving product efficacy and being proactive against herbicide resistance.  As labels often describe, there is a specified application timing window for maximum product efficacy; however, as we get outside that window, we inherently are going to ask more out of products than initially intended. 

When this occurs, we are putting more pressure on post emergent herbicide applications to achieve a weed control, instead of putting these products in a system to maintain efficacy and manage herbicide resistance. 

The Takeaway

To learn more about the nitrogen cycle and how to properly manage the nutrients in your soil, contact your local Simplot Grower Solutions Crop Advisor.