It’s no secret that weed resistance has evolved into one of the top issues for soybean growers. With each additional year of using ineffective herbicide chemistries and weed management strategies, weeds have the opportunity to adapt and develop resistance.

In order to delay the development of weed resistance, most universities say it’s important to implement a combination of cultural practices in conjunction with a strong herbicide program containing overlapping residuals. This includes using multiple, effective sites of action (SOAs) that directly target the spectrum of weeds present.

Syngenta developed a resistance modeling program to analyze different weed management scenarios in which various programs were considered.

1. Single SOA program: No pre-emergence herbicide, followed by 2 post-emergence applications of dicamba.
   • SOAs: Group 4
   • Predicted results: Repeated use of a single SOA program like this one could lead to the development of resistance after only a few years.

2. Three SOAs program: Boundary^®5 EC herbicide pre-emergence, followed by dicamba post-emergence.
   • SOAs: Groups 4, 5 and 15
   • Predicted results: Applying a pre-emergence herbicide with multiple, effective SOAs can help extend the life of the technologies, but it won’t make up for applying a post-emergence herbicide with only a single SOA. Resistance could develop in several years.

3. Three SOAs program with overlapping residuals: Boundary pre-emergence, followed by a tank mix of dicamba plus Dual Magnum^® post-emergence.
   • SOAs: Groups 4, 5 and 15
   • Predicted results: Overlapping residuals and utilizing a herbicide program with multiple, effective SOAs in both the pre-emergence and post-emergence applications can delay the development of resistance for many years.

4. Four SOAs program: Boundary herbicide pre-emergence, followed by a tank mix of dicamba plus Prefix^® herbicide post-emergence.
   • SOAs: Groups 4, 5, 14 and 15
   • Predicted results: Continual use of a strong soybean herbicide program with multiple, effective SOAs in both the pre-emergence and post-emergence applications that directly target the spectrum of weeds on your farm has the potential to delay the development of resistance for up to 2 decades longer than a program with a single SOA.

For more tips on how to win the battle against resistant weeds, visit ResistanceFighter.com.

Sign up for the Know More, Grow More Digest to receive twice-monthly agronomic e-mail updates pertinent to your area.

All photos are either the property of Syngenta or are used with permission.

Syngenta hereby disclaims liability for third-party websites.