As weed resistance continues to evolve, it is critically important to develop and utilize effective weed management strategies. Pre-emergence herbicide applications offer a valuable tool to prevent or reduce weed infestations early in the season, giving the turf a chance to thrive and compete with the weed population.
Compared to post-emergence, pre-emergence herbicide applications have unique challenges that make effective control difficult. In post-emergence applications, the spray targets the weed leaf directly. While these applications are still prone to off-target movement (i.e., drift and volatilization), UV-degradation, and challenges with uptake, the herbicide can typically be effective provided that it hits the leaf and isn’t antagonized by spray tank water or other chemicals.
By contrast, pre-emergence applications target the soil, which is a complex physical and chemical matrix that differs on every site. The herbicide must successfully reach the soil surface, and then move to and stay at the correct depth for the application to be effective. The active ingredient must remain active long enough to suppress weed seed germination over an extended period of time.
Some herbicides adsorb to organic matter readily and are difficult to move down into the soil. These herbicides may be more prone to UV degradation. Other herbicides do not adsorb to organic matter and tend to be difficult to keep in the soil. These herbicides are more prone to leaching. In both cases, loss of the active ingredient results in poor weed control.
The use of adjuvants with pre-emergence herbicide applications is rising. The Council of Producers & Distributors of Agrotechnology (CPDA) offered a webinar in December of 2023 that discussed the various benefits of using adjuvants to enhance residual weed control. The presenter, CPDA Director of Education Johnnie Roberts, discussed the difference in herbicide chemistry – the herbicides that tend to adsorb to organic matter more readily (e.g., pendimethalin) tend to be more oil soluble, and can benefit from oil-based adjuvants. The herbicides that tend to adsorb to organic matter less readily (e.g., atrazine) tend to be more water soluble, and can benefit more from polymers or resins.
Figure 1: A randomized field trial one day after application of a pre-emergence herbicide. The use of an Exacto adjuvant resulted in visibly less moisture at the plot surface. The adjuvant helped to move the spray down into the soil, preventing the risk of UV-degradation of the herbicide at the soil surface.
The value of adjuvants with pre-emergence herbicide applications is visible in Figure 1, where the use of an Exacto adjuvant helped the spray move further into the soil, and off the surface where it could have been susceptible to UV-degradation. In Exacto’s field research studies, the use of the adjuvant Inlay with the herbicide application has extended weed control by 15 to 40% between 45 to 90 days after application (Figure 2).
Figure 2: Crabgrass control in Raleigh, NC on a sandy soil. Herbicides were applied to bare ground and crabgrass control was evaluated over time. Herbicides began to lose their effectiveness around 30 days after application, but the use of Exacto’s adjuvant Inlay extended residual weed control by 15 to 40% between 45 to 90 days after application. Lower case letters indicate statistically significant differences at the alpha=0.05 level.
There are proven adjuvant options on the market today for optimizing pre-emergence herbicide applications, and using these products can extend residual weed control to get more out of every application. INLAY™ is a deposition-aid specially designed for pre-emergence herbicides, and this product gives turf managers more time between sprays by extending weed control.
This demonstration of INLAY shows how this deposition aid can keep herbicide in the soil even after multiple rain events.
INLAY is a deposition aid that improves effectiveness of pre-emergence herbicide applications. This adjuvant helps improve deposition and distribution of the spray application into the soil where weed seeds germinate. Here is why pre-emergence applications should include Inlay:
Spray Delivery: Inlay provides drift control and improves deposition of the spray, helping the active ingredient reach its target in the soil.
Extended Control: Inlay extends residual weed control by up to 40% between 45 to 90 days after application.
Improved Flexibility: Lawn care operators have more time before follow-up post-emergence applications are required, and the turf stand is more competitive against weeds early in the growing season.
Science is still evolving when it comes to identifying the complex relationships between spray characteristics, herbicide chemistry, soil chemistry, and weed ecology. These relationships will become more complex as spray application technology evolves, and as tank mixes become more complex and concentrated. These challenges exist with a backdrop of increasing herbicide resistance in weed populations which threatens the weed control tools we have available today. Adjuvants offer additional flexibility, improved performance, and greater efficiency, and these technologies will continue to be more and more important in the future. Exacto is innovating adjuvants to help bridge from solving the application problems of today, to optimizing the emerging technologies of the future.
Surfactants are widely used across the world – in fact, you probably use surfactants every day in soaps, detergents, toothpaste, cosmetics, and countless other applications. Surfactants are just as important in agriculture and turf and understanding how and when to use the right surfactant can make or break a successful application.
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