Fall – Winter Herbicide Application: Weather Impacts and Cautions to Consider

As 2023 turned into 2024 rather quickly, we often think about the new challenges and changes that come with a new spring just around the corner.

In certain parts of the upper southern business unit, weather dependent, planting can begin as early as 6 weeks from now. However, weather patterns in the fall of 2023 left much of the area in what could be considered one of the driest falls/winters many can remember. As fall faded into winter and unsettled beds, lack of rainfall, and lack of predicted rainfall put us in a mid-winter herbicide application time frame.

A couple of items we wanted to highlight as we make our way into early 2024 is what impact late fall-mid winter herbicide applications can have on our subsequent crop and cautions that should be considered with applications being made currently. 

Fall herbicide programs are becoming more of staple in southern row crop production for controlling problematic fall/winter weed species. These applications reduce the soil seed bank and keep fields as clean as possible to minimize weed control pressure placed on spring burndown applications.

In addition to these two primary focus points, there are several additional benefits to a fall herbicide program. For more information please see the 3 Part Fall Burndown Series from last fall.

To achieve maximum efficacy, we typically want to target fall herbicide applications between Mid-October to Mid-November; however, due to previously mentioned weather constraints of late 2023 and early 2024 applications are currently being made that could put growers in a sensitive time frame for plant back restrictions (See Table 1).

Typically, we see greater residual control due to decreased microbial activity, lower temperatures, shorter day length and slower herbicide breakdown in the fall and winter.

However, due to the unique timeframe we are currently in, where beds are finally settling, and rainfall is adequate to activate residuals we are beginning to approach plant back restrictions to spring crops. For lack of better terms fall-winter applied residual herbicide applications could be categorized as self-imposed carryover situation if application timing, herbicide active ingredient, and weather are compromised or applied too late to an early planted sensitive crop.

During the next few weeks, if herbicide applications are being made, it is crucial to check plant back restrictions and in places where applications were made this fall, lack of rainfall and dissipation rate should be considered as well when considering what to plant on those acres, especially on uncommitted acres.

Fall herbicides are a great method of weed control especially when it comes to early planted crops, and the later we can apply these applications often the length of weed control improves. However, applications during the current time window should be advised with caution as plant back windows are getting narrow.

During this time as your growers are making applications, please consult label plant back restrictions to ensure a great spring crop. Please consult any of your local Agronomic Sales Enablement Team for any further questions and product options.

Table 1: Commonly applied herbicides in southern production systems.

Table adapted from 2024 Weed Management Suggestion for Mississippi Row Crops Pages 21-23

1. Replant only with grain sorghum safened for applications of Group 15 Herbicides
2. Rotational crop restrictions are dependent on herbicide application rate, soil pH, rainfall following application, soil texture, or application technique (PRE, POST, etc). Consult the product label for specific information.
3. Rotation interval applies for soybean for STS tolerant soybean
4. For additional information, please see these websites: www.agrian.com, www.cdms.net, or www.greenbook.net