We asked representatives from several pesticide companies: We’re hearing that herbicide resistance is becoming more of a factor in golf course maintenance. Are superintendents aware of this? What should they do to combat potential resistance? Here’s what they had to say:

Jason Fausey | Weed Scientist, Nufarm

Superintendents are aware of less than previously achieved control provided by herbicides. Yet, until they encounter herbicide-resistant weeds, it seems they underestimate the magnitude of the situation. For instance, when managing Poa annua, resistance is often cited as the reason for a few escaped weeds. However, once herbicide resistance has developed, you suddenly find complete survival of weeds to the entire class of chemistry, which worked in the past. The key to a successful resistance-management program is to ensure maximum results and having a reason and a goal for every herbicide application on the course. Product selection and utilization is critical for a balanced program and each herbicide is unique and has its own optimum-use pattern for rate, timing, temperature, spray volume and coverage that needs to be followed.

Kyle Miller | Senior Technical Specialist, BASF

As a rule, most superintendents do not perceive a problem with weed resistance on golf courses. However, we do have certain situations where resistance has been documented or appears to be present. This usually occurs when a single active ingredient has been used for many, many years on the same area of the course. We most often see this with pre-emergent annual grass herbicides since they are routinely used as a single active ingredient (one mode of action). Most broadleaf herbicides contain numerous active ingredients with different modes of action reducing the likelihood for resistance. The solution is fairly simple — incorporate different modes of action into your weed control program, just like we do with fungicides.

Colleen Tocci | Marketing Manager, Engage Agro USA

While superintendents are aware of herbicide resistance, they may not be aware of techniques to prevent it if it’s not directly impacting them. Unfortunately, products with new mechanisms of action (MOA) to combat herbicide resistance aren’t in any advanced state of development, so we rely on products currently in the market. In addition to glyphosate products, weeds such as annual bluegrass, goosegrass and smooth crabgrass are building resistance across the U.S. to ACCase, ALS, and microtubule assembly inhibitors. To minimize resistance potential, a proactive approach by rotating products with different MOAs now can reduce the potential for resistance later.

Dean Mosdell | Western Field Technical Manager, Syngenta

Certain weeds are more inclined to develop resistance in turf. The most common are annual grasses that develop seedheads below typical mowing heights, like annual bluegrass and goosegrass. To combat potential resistance, superintendents should have a weed management plan, including a map of weed encroachment, and evaluate changes throughout the season. There are several herbicide options to slow the development of resistant biotypes — pre-emergence, selective post-emergence and if necessary, spot treatments with non-selective herbicides. Some options work best if used together such as a broadcast preemergence with a post-emergence to control escapes. Superintendents should also read the resistance management language on labels concerning the number of applications and herbicide rotation. Some modes of action, such as ALS and PS-2 inhibitors, can quickly select for resistant biotypes.

Dave Loecke | Herbicide Product Manager/ PBI-Gordon

Herbicide resistance in weeds isn’t new, but it may be hitting the golf industry more than ever. Fortunately, we have a greater understanding of what causes resistance, and we have more proven products to help fight it. The key to resistance management is rotating not just products, but modes of action. Rotating between brands that use the same mode of action won’t slow resistance. But we can fight resistance development through a rotation program that uses different modes of action or products with multiple modes of action.

 

Jay Young | Herbicide Brand Manager/FMC

Herbicide resistance is becoming a concern. In order to combat resistance, turf professionals need to incorporate a rotational program into their weed management programs. Rotation of chemistries has played a role in slowing down resistance in disease management and a similar philosophy needs to be taken when developing an effective and sustainable weed management program. In addition, many researchers are mentioning using combination products that contain different modes of action to reduce development of weed resistances.

 

Jeff Michel | Herbicide Product Manager, Bayer

Superintendents are aware of the importance of weed resistance, but it’s important to remember that herbicide resistance isn’t found equally in all parts of the U.S. It’s often localized on a course or region. While annual bluegrass and goosegrass are most frequently reported with control issues, the recommended way to manage the development and spread of resistant weed populations is to use effective herbicides with different mechanisms of action in tank mixtures, rotation, or in conjunction with sound cultural practices which minimize weed pressure and maximize weed control.

COVER PHOTO BY CHARLES MANN/SIGNATURE/ISTOCK