By Scout Nelson
Fall-applied herbicides can help farmers manage kochia and other weeds that emerge early in the growing season. However, the effectiveness of these products depends on weather conditions, soil moisture, and the herbicides used. Research from South Dakota State University (SDSU) showed that combining herbicides from different groups can provide better kochia control than using a single product.
Eric Jones, Assistant Professor and SDSU Extension Weed Management Specialist, along with Jill Alms and David Vos, examined fall herbicide treatments for kochia management. The study took place at the SDSU Southeast Research Farm in Beresford, South Dakota, to compare the effectiveness of different herbicides and mixtures.
Why Fall Herbicide Applications Matter
Residual herbicides help prevent weed seeds from germinating, reducing competition between weeds and crops. They also help farmers reduce their reliance on postemergence herbicides, which are applied after weeds emerge.
However, weather can affect how well residual herbicides work. Dry conditions at planting may prevent herbicides from moving into the soil where weed seeds germinate. Wet conditions can delay fieldwork and herbicide applications, allowing weeds to emerge and compete with crops.
Fall applications offer another way to manage early-emerging weeds. Snowmelt and early spring rainfall can move herbicides into the soil layer where young weeds begin growing. This timing can reduce the risk of poor application conditions during spring planting.
Fall herbicide applications do not eliminate the need for weed control throughout the growing season. However, they can provide an important first step in a broader weed management plan.
Herbicide Resistance Creates New Challenges
Flumioxazin, sold under brand names such as Valor and Panther, is commonly used for fall weed control in South Dakota. Its properties support residual activity against several weeds.
However, repeated use of the same herbicide group can encourage resistant weeds to develop. Kochia populations resistant to Group 14 herbicides have been identified in Canada, North Dakota, and South Dakota.
This growing concern raises an important question for farmers: “What is as effective, and what other herbicides should be used as well?”
Using herbicides with different modes of action can help reduce reliance on a single group and improve the chances of effective weed control.
SDSU Research Compares Herbicide Treatments
Researchers applied several herbicides and mixtures on November 4, 2025, and evaluated kochia control on May 11, 2026. Each treatment was tested three times. The kochia population at the research site was susceptible to Group 14 herbicides, which is an important factor when interpreting the results.
The study included single products such as Dual Magnum, Prowl, Tricor, Valor, and Zidua. It also tested mixtures, including Dual Magnum with Zidua, Fierce EZ, Tripzin, Dimetric Charged, and Fierce MTZ.
The results showed that only two single-herbicide treatments, Valor and Zidua, provided more than 70% kochia control. The other single products did not exceed 67% control.
In comparison, all herbicide mixtures provided more than 80% kochia control. The two-herbicide mixtures achieved control ranging from 85% to 99%, while the three-herbicide mixture provided about 92% control.
These findings suggest that combining herbicides can improve weed control compared with using individual products. However, the results come from one location and one year, so additional research is needed to understand how the treatments perform under different conditions.
Important Considerations for Farmers
The researchers selected herbicides based on a soybean crop planned for the following spring. Not every product is suitable for every crop, and some herbicides have planting restrictions.
For example, pendimethalin, sold as Prowl H2O, has restrictions that farmers must consider when planning a corn crop. The single-herbicide treatments also used maximum labeled rates, which could limit opportunities for additional applications of those products during the growing season.
Farmers should review the latest South Dakota Pest Management Guides and individual herbicide labels before making application decisions. These resources provide details about application rates, weed control, crop safety, and planting restrictions.
Photo Credit: South Dakota State University
Categories: South Dakota, Crops