Interaction of PS II‐ and HPPD‐Inhibiting Herbicides for Control of Palmer Amaranth Resistant to Both Herbicide Sites of Action

Abstract

Palmer amaranth (Amaranthus palmeri S. Watson) resistant to post-emergence (POST) applications of photosystem (PS) II-and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides has been confirmed in a continuous corn (Zea mays L.) seed production field in Nebraska. Field studies were conducted in 2014 through 2016 near Shickley in Fillmore County, Nebraska, to determine the response of Palmer amaranth to PS II-and HPPD-inhibiting herbicides applied pre-emergence (PRE) and to their tank-mixtures applied PRE or POST. Results from the dose-response study indicated that atrazine at 3757 and 17,920 g a.i. ha-1 applied PRE provided 25 and 45% Palmer amaranth control, respectively, at 28 d after treatment (DAT). Mesotrione and isoxaflutole doses required for 90% control were 1030 and 1140 g ha-1 , respectively. To determine the interactions of mesotrione, tembotrione, or topramezone tank-mixed with atrazine applied POST, Colby's equation was used to calculate the expected Palmer amaranth control achieved with those tank-mixtures compared to a nontreated control. Based on Colby's equation, additive interactions occurred for Palmer amaranth control, density reduction, and biomass reduction when atrazine tank-mixed with mesotrione or isoxaflutole was applied PRE at all rate combinations. However, synergistic interactions occurred when mesotrione or topramezone tank-mixed with atrazine was applied POST. The results indicated that Palmer amaranth from Nebraska is resistant to both PS II-and HPPD-inhibiting herbicides applied PRE or POST alone; however, they can be applied POST in a tank-mixture with different site of action herbicides for effective control and to reduce the risk of herbicide resistance evolution.

Utility of isoxaflutole-based herbicide programs in HPPD-tolerant cotton production systems

“…While the addition of IFT did not enhance Palmer amaranth control at this location, IFT did add an additional site of action without detriment to weed control, potentially aiding in the delay of herbicide-resistance evolution. In production areas where Palmer amaranth may be resistant to HPPD, PSII, or both sites of action, the use of IFT with a PSII herbicide such as fluometuron may still be able to provide some control where fluometuron alone may not, due to the synergistic behavior that has been shown to overcome resistance to these sites of action (Chahal and Jhala 2018;Chahal et al 2019).…”

“…The addition of IFT will provide an additional herbicide site of action for cotton production acres while planted to cotton, which will be paramount for combating further herbicide resistance evolution. Even with HPPD-inhibiting herbicide resistance already present in Arkansas (Heap 2021) with resistance to mesotrione, combinations of HPPD-inhibiting herbicides such as IFT with PSII inhibiting herbicides, such as fluometuron in cotton, have been shown to overcome resistance to either HPPD-or PSII-inhibiting herbicides by Palmer amaranth (Chahal and Jhala 2018). It should be noted that successful, season-long weed control was attained only through the use of complete herbicide programs that used multiple effective sights of action, and these strategies, as well as the incorporation of holistic integrated weed management strategies, will need to be implemented to aid in the longevity of these new technologies (Norsworthy et al 2012).…”

“…Typically, IFT has been labeled for use in corn production as a preemergence (PRE) or early postemergence (EPOST) herbicide for the control of smallseeded broadleaf weeds and grasses (Anonymous 2019;Pallett et al 1998). It has been previously reported that IFT is an effective tank-mixture partner with photosystem II (PSII)-inhibiting herbicides for the control of glyphosate-resistant Palmer amaranth when used as a part of a glufosinate-based herbicide programs (Chahal et al 2019;Chahal and Jhala 2018;Jhala et al 2014;Stephenson and Bond 2012).…”

“…When applied postemergence (POST), the combination of HPPD-and PSII-inhibiting herbicides has been shown to have a synergistic effect, whereas PRE applications of similar tank-mixtures were additive in nature (Chahal and Jhala 2018;Kohrt and Sprague 2017;Meyer et al 2016). Although HPPD-resistant populations of Palmer amaranth have been documented, the pairing of HPPD-inhibiting herbicides such as IFT with PSII-inhibiting herbicides has been shown to be effective at overcoming resistance to either site of action (Chahal et al 2019;Chahal and Jhala 2018). In IFT-tolerant cotton, producers will have the flexibility to apply IFT PRE or EPOST.…”

Effective dose of atrazine required to complement tolpyralate for annual weed control in corn

“…Herbicides such as atrazine that inhibit the photosystem II (PS II) protein complex are commonly applied in a mixture with HPPD inhibitors to improve weed control (Armel et al 2005;Chahal and Jhala 2018;Chahal et al 2019;Johnson et al 2002;Kohrt and Sprague 2017;Whaley et al 2006;Willemse et al 2021a;Williams et al 2011;Woodyard et al 2009). The PS II inhibitors compete with plastoquinone for the Q B binding niche on the D1 protein of the photosynthetic electron transport chain (Hess 2000).…”