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Proposed Registration of Tiafenacil Herbicide

Soybean farming today is significantly compromised by the persistent and widespread occurrence of herbicide-resistant (HR) weeds. Gone are the days when a shot or two of glyphosate applied to glyphosate-resistant (GR) crops can be the sole weed control system used by farmers.

In a July 31, 2020 press release titled “EPA Proposes Registration of New Herbicide to Aid in Resistance Management”, the US-EPA “is proposing to register a new active ingredient, tiafenacil, a contact herbicide” that can be used for preplant and preemergence burndown application in corn, cotton, soybeans, and wheat. According to the press release, tiafenacil provides an alternative for controlling GR Palmer amaranth and suppressing GR marestail.

Tiafenacil is a Group 14 herbicide (PPO inhibitor). This group also includes the active ingredients fomesafen (Reflex), flumioxazin (Valor, Panther SC), and saflufenacil (Sharpen), among others. According to information in the article titled “Biochemical and physiological mode of action of tiafenacil, a new protoporphyrinogen IX oxidase-inhibiting herbicide” [Pesticide Biochemistry and Physiology 152 (2018) 38-44,], tiafenacil is a non-selective pyrimidinedione PPO inhibitor that exhibits effective herbicide activity against both monocot and dicot weeds.

According to the Tiafenacil proposed label, the following stipulations (among others) are made. 1) “Tiafenacil 70WG is a nonselective contact (burndown) herbicide used to control or suppress a broad spectrum of emerged broadleaf and grass weeds. Tiafenacil 70WG has excellent burndown activity on most young (generally less than 5 inches tall) annual weeds and suppresses the growth of perennial weeds by desiccating green foliage.” 2) Tiafenacil rapidly degrades following its application, and thus has no preemergence activity. 3) A methylated seed oil/crop oil concentrate or nonionic surfactant must be used when applying Tiafenacil or reduced performance will occur.

Click here for a “Review of Benefits for the Proposed new Registration of the Herbicide Tiafenacil...” by the US-EPA Office of Chemical Safety and Pollution Prevention, Biological and Economic Analysis Division (BEAD). Included in this analysis is a list of the 23 target weeds (both broadleafs and grasses) as identified by the registrant, ISK Biosciences Corporation.

The EPA press release contains the following points. 1) “The database for tiafenacil indicates the chemical is generally low-risk to non-target organisms other than plants; thus, most mitigation measures for this new herbicide deal with avoiding contact with non-target plants.” 2) “EPA has not identified any dietary, residential, aggregate, or occupational risks of concern for human health; therefore, no mitigation is being proposed.”

As with any herbicide, both past and future, the value of this new herbicide active ingredient will only be realized if it is used in accordance with the forthcoming label, and then only if used against weeds that are stipulated as target weeds on the label.

LGH Note: To my knowledge, there is no trade name for this new herbicide at this time. It is assumed that once/if registered, it will be given a trade name then.

Composed by Larry G. Heatherly, Aug. 2020,