By UPL

Lynn Justesen, UPL Row Crop Technical Services Lead

Ryan Bryant-Schlobohm, Ph.D., CCA, UPL Technical Services Manager

Weeds compete with crops for key resources, directly reducing yield potential and producer profitability. Integrated pest management programs are a focal point of sustainable management, and herbicides provide proven performance to pest management programs – increasing profitability, efficiency, and sustainability of modern cropping systems. Post-emergence herbicide applications are a focal point of many management programs, and optimization of these applications provides direct return for growers. When planning a successful post-emergence herbicide application, growers and consultants should consider application timing, weed size, weather conditions, multiple modes of action, and proper adjuvants.

Application Timing and Weed Size

Proper timing is a priority for optimized herbicide applications. Growers should consider the labelled crops heights/growth stages and weed size to achieve best performance of a post-emergence herbicide application. Many modern herbicides are most effective when targeting small, actively growing weeds – ideally less than 2-3” in height. Additionally, timing these applications to complement the residual activity of pre-emergence herbicide will provide further benefits in managing weeds throughout critical points of crop development. Ensuring weeds are controlled during early vegetative growth stages should be a focal point of any herbicide program to ensure yield potential is not limited due to excessive weed competition. Below is a graphic that shows the effect weed size at the time of application from IMIFLEX™ Herbicide with igrowth^® sorghum. The smaller the weeds, the greater the level of efficacy that can be achieved.

Wheat is a good example of a crop who’s yield potential positively responds to the early control of troublesome grass and broadleaf weeds. When we consider an all-in-one wheat herbicide like BATALIUM^® AMPED™, this is a product that allows for a wide application window between wheat reaching the 2-leaf stage and 60 days before harvest all while maintain a high level of crop safety. Timing this application early in the season to small, actively growing weeds allows wheat growers to control a long list of grass and broadleaf weeds that have the potential to rob yield potential.

Weather Conditions

Weather before and after a post-emergence herbicide application is an important point to consider when timing your application. The key is to time these applications around periods that avoid rainfall during the rain-fast window of the herbicide and to make applications when weeds are actively growing. Periods of excessive heat, drought, or cold stress can reduce the pace at which herbicides act on the weeds. If periods of stress are unavoidable, utilizing a more aggressive adjuvant package/combination can help overcome some of the drop in performance.

IMIFLEX Herbicide performs best when used on weeds that are small and actively growing. When used with igrowth sorghum, drought and heat stress can be a common occurrence in many of the key sorghum growing regions of the US. When making a post-emergence application in these situations, opting for an adjuvant combination that features a 2% v/v of MSO and 5% v/v of UAN can help optimize efficacy when targeting weeds that are experience environmental stress.

Multiple Modes-of-Action

The foundation to successful herbicide programs is a solid pre-emergence herbicide. Look to layer the residuals of a post-emergence application with the residual timeline of the pre-emergence application. When making any herbicide application, multiple modes of action are key to sustainable weed management programs. Utilizing herbicide combinations that expose troublesome weeds to multiple effective chemistries will help to optimize control and promote the longevity of effective products. Whether this is achieved through a tank-mix or pre-mix, control of weeds like kochia, common lambsquarters, redroot pigweed, and many others will be optimized when growers use multiple effective herbicides to combat these weeds.

BATLIUM AMPED Herbicide is an example of a product that provides multiple modes of action to target difficult to control weeds like kochia. Made of flucarbazone-sodium, fluroxypyr, and bromoxynil (Groups 2, 4, and 6, respectively), this product provides 3 modes of action in a combination that has a unique finishing power on weeds like kochia, lambsquarters, and many other broadleaf and grass weeds.

When making weed control plans, the addition of a group 15 herbicide in sorghum or the use of a multi-mode of action product like BATALIUM AMPED in wheat will aid in providing thorough weed control leading up to harvest.

Proper Adjuvants

Adjuvants are a crucial part of post-emergence herbicide applications. Herbicide labels will list adjuvant requirements of products. When implementing a tank-mix, it’s important to follow the adjuvant requirements of the most restrictive herbicide label. Adjuvants can include a range of products, but are generally focused on non-ionic surfactants, crop-oil concentrates, methylated seed oils, high-surfactant oil concentrates, and nitrogen sources. Depending on the type of herbicide, adjuvant use will have different objectives to obtain desired results. When using contact herbicides, adjuvants that improve coverage, deposition, and cuticle penetration will likely be called for on the herbicide label. Systemic herbicides will follow many of the same principles and will often feature a call for adjuvant combinations that enhance cuticle penetration and uptake of the active ingredients. Understanding your herbicides of choice and the situation they’re being applied in will help clarify your adjuvant objectives.

IMIFLEX Herbicide is an example of a product that has several adjuvant combinations to choose from. These decisions can largely be dictated by weed size and environmental stress. In periods of low environmental stress a combination of NIS and AMS is an acceptable option. However, if environmental stress increases, a grower may choose to use a higher rate of MSO with UAN instead. Thicker cuticles of weeds in response to heat and drought stress can be overcome to an extent with adjuvants that promote a greater level of penetration. Growers should be aware that certain adjuvant combinations have the potential for increased potential of crop response. Generally these reactions are only cosmetic to the crop, while providing a higher level of efficacy towards the target weeds. Below is data comparing different adjuvant combinations with IMIFLEX Herbicide and igrowth sorghum. A few key points with this data are that it shows the general trend of higher crop response from the addition of UAN, in addition this data highlights the slight increase in crop response you may encounter with MSO + Nitrogen source combinations. As the impact to the crop is usually only cosmetic, the heightened activity of different adjuvant combinations provides an opportunity for optimized herbicidal activity on tough to control weeds.

Additionally, different types of tank-mixtures can require different approaches with adjuvants. BATALIUM AMPED Herbicide used by itself or tank-mixed with dry formulated herbicides or EC-based herbicides used at less than 8 fl oz/A requires a basic blend or NIS + Nitrogen Source combination. Whereas when BATALIUM AMPED is tank-mixed with an EC-based herbicide used at a rate greater than 8 fl oz/A, the main requirement is a nitrogen source with NIS being optional if not restricted by the tank-mix partner.