Hydrolytic Activation Kinetics of the Herbicide Benzobicyclon in Simulated Aquatic Systems

Abstract

Herbicide resistance is a growing concern for weeds in California rice fields. Benzobicyclon (BZB; 3-(2-chloro-4-(methylsulfonyl)benzoyl)-2-phenylthiobicyclo[3.2.1]oct-2-en-4-one) has proven successful against resistant rice field weeds in Asia. A pro-herbicide, BZB forms the active agent, benzobicyclon hydrolysate (BH), in water; however, the transformation kinetics are not understood for aquatic systems, particularly flooded California rice fields. A quantitative experiment was performed to assess the primary mechanism and kinetics of BZB hydrolysis to BH. Complete conversion to BH was observed for all treatments. Basic conditions (pH 9) enhanced the reaction, with half-lives ranging from 5 to 28 h. Dissolved organic carbon (DOC) hindered transformation, which is consistent with other base-catalyzed hydrolysis reactions. BH was relatively hydrolytically stable, with 18% maximum loss after 5 days. Results indicate BZB is an efficient pro-herbicide under aqueous conditions such as those of a California rice field, although application may be best suited for fields with recirculating tailwater systems.

Benzobicyclon as a Post-Flood Option for Weedy Rice Control

“…at 32 C compared to 18 C. Large crabgrass was also twice as susceptible to mesotrione at 85% relative humidity as at 30% relative humidity (Johnson and Young 2002). The results of the percentage control data suggest similarities to the research conducted by Williams and Tjeerdema (2016).…”

“…The increased benzobicyclon activity could be due to environmental conditions such as temperature, relative humidity, or pH of water. The parent molecule, benzobicyclon, is a pro-herbicide that must be hydrolyzed to benzobicyclon hydrolysate to exhibit herbicidal activity (Komatsubara et al 2009; Williams and Tjeerdema 2016). Williams and Tjeerdema (2016) documented that the conversion of benzobicyclon to benzobicyclon hydrolysate increases as a function of temperature and pH of water.…”

“…The parent molecule, benzobicyclon, is a pro-herbicide that must be hydrolyzed to benzobicyclon hydrolysate to exhibit herbicidal activity (Komatsubara et al 2009; Williams and Tjeerdema 2016). Williams and Tjeerdema (2016) documented that the conversion of benzobicyclon to benzobicyclon hydrolysate increases as a function of temperature and pH of water. Johnson and Young (2002) confirmed that another triketone herbicide, mesotrione, has increased activity on certain weed species as temperature and relative humidity increases.…”

Benzobicyclon carryover to crops in the Mississippi Delta

“…Benzobicyclon is a pro‐herbicide that requires water to convert benzobicyclon to its herbicidal form, benzobicyclon hydrolysate (Komatsubara et al., 2009; Willimas et al., 2016). However, benzobicyclon hydrolysate has some leaching potential due to its aqueous solubility of 9.7 × 10 −4 oz gal −1 (Williams et al., 2016). The parent molecule, benzobicyclon, has a low leaching potential with a K oc of 1104 (Kegley, Hill, Orme, & Choi, 2019).…”

“…Similarly, another triketone herbicide, mesotrione, has a high leaching potential with a K oc of 80 (Riddle, O'Sullivan, Swanton, & Van Aker, 2013). Conversion of benzobicyclon to benzobicyclon hydrolysate can be affected by the pH of water (Williams et al., 2016). However, benzobicyclon persistence has not been tested in Mississippi Delta rice systems, and sensitivity to rotational row crops is not known.…”