Spring-applied triclopyr mixtures for bermudagrass (Cynodon dactylon) suppression in sugarcane

Authors: Spaunhorst, Douglas

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sugarcane harvested as seed-cane introduces the potential for bermudagrass to reinfest fields. Research was conducted 6 to 9 months after sugarcane harvest for seed-cane to evaluate bermudagrass management with photosystem II (PSII)- and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibitor herbicides applied alone or tank-mixed with triclopyr. Mixing diuron at 2.8 kg ha-1 plus clomazone at 1.5 kg ha-1 or triclopyr at 1.1 kg ha-1 and hexazinone at 0.74 kg ha-1 plus triclopyr applied in mid-February injured bermudagrass 85 to 86% and greater than diuron or hexazinone applied alone (16 and 10%) in mid-March. By early April, bermudagrass began to recover from the herbicide treatment and was 45 to 56% for these combination treatments, however, control differences were similar to the earlier rating. A mid-March application of these treatments indicated similar control trends when evaluated in early April. By mid-May, however, no treatment resulted in greater than 18% bermudagrass injury. With the exception of clomazone plus diuron applied mid-March (19% sugarcane injury), by early April, no treatment resulted in greater than 6% sugarcane injury and injury was no greater than 1% by mid-May. In mid-May, mid-April application of topramezone at 0.025 kg ha-1 in combination with triclopyr at 1.1 kg ha-1 resulted in 62% bermudagrass injury, which was similar to that reported with other topramezone rates in this combination (0.012 and 0.037 kg ha-1) (54 to 69%) and mesotrione applied at 0.105 kg ha-1 plus triclopyr (32%) or in a 4-way mix with atrazine, mesotrione, S-metolachlor, and triclopyr (47 to 55%), and greater than all other treatments. Results were similar at this rating interval for LPOST treatments applied in early May. In August, averaged across herbicide treatments, the early-season application timing resulted in greater bermudagrass density than the late-season timing (71 vs 54 m-2). Averaged across application timing, the lowest numeric bermudagrass density at this time was observed following application of topramezone at 0.037 kg ha-1 applied with triclopyr (27 m-2). This number was statistically similar to topramezone applied alone at the highest rate (59 m-2) or in combination with triclopyr (36 to 39 m-2) , mesotrione plus triclopyr alone (45 m-2) or in 4-way combination (49 to 56 m-2), and triclopyr and diuron each applied alone (40 and 43 m-2, respectively). Sugarcane stalk height and population were not influenced by herbicide program or application timing. Data from this study showed the flexibility of triclopyr when mixed with several currently labeled HPPD- or PSII-inhibitor herbicides for bermudagrass management in sugarcane. Greater flexibility in application timing for HPPD-inhibitor herbicides when compared with PSII-inhibitor herbicides (diuron or hexazinone), and mixed with triclopyr, may provide an opportunity for sugarcane growers to suppress established bermudagrass in April and May with minimal sugarcane injury before rapid sugarcane growth begins.

Technical Abstract: Sugarcane infested with bermudagrass and harvested as seed-cane introduces the potential for weedy vegetative propagules to reinfest fields. Research was conducted in 2018-2019 the spring following sugarcane harvest for seed-cane to evaluate bermudagrass management with photosystem II (PSII)- and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibitor herbicides applied alone or tank-mixed with triclopyr. Combinations of diuron at 2.8 kg ha-1 with clomazone at 1.5 kg ha-1 or triclopyr at 1.1 kg ha-1 and hexazinone at 0.74 kg ha-1 with triclopyr applied EPOST in mid-February injured bermudagrass 85 to 86% and greater than diuron or hexazinone applied alone (16 and 10%) in mid-March. By early April, injury had dropped to 45 to 56% for these combination treatments, however, control differences were similar to the earlier rating. LPOST mid-March application of these treatments indicated similar control trends when evaluated in early April. By mid-May, however, no treatment resulted in greater than 18% bermudagrass injury. With the exception of clomazone plus diuron applied LPOST at the early April evaluation timing (19%), no treatment resulted in greater than 6% sugarcane injury and injury was no greater than 1% by mid-May. In mid-May, mid-April EPOST application of topramezone at 0.025 kg ha-1 in combination with triclopyr at 1.1 kg ha-1 resulted in 62% bermudagrass injury, which was equivalent to that observed with other topramezone rates in this combination (0.012 and 0.037 kg ha-1) (54 to 69%) and mesotrione applied at 0.105 kg ha-1 plus triclopyr (32%) or in a 4-way mix with atrazine, mesotrione, S-metolachlor, and triclopyr (47 to 55%), and greater than all other treatments. Crop injury was no greater than 2%. Results were similar at this rating interval for LPOST treatments applied in early May. In August, averaged across herbicide treatments, EPOST application timing resulted in greater bermudagrass density than LPOST timing (71 vs 54 m-2). Averaged across application timing, lowest numeric bermudagrass density at this time was observed following application of topramezone at 0.037 kg ha-1 applied with triclopyr (27 m-2). This number was statistically similar to that observed for topramezone applied alone at the highest rate (59 m-2) or in combination with triclopyr (36 to 39 m-2) , mesotrione plus triclopyr alone (45 m-2) or in 4-way combination (49 to 56 m-2), and triclopyr and diuron each applied alone (40 and 43 m-2, respectively). Crop stalk height and population differences were not influenced by herbicide program or application timing. Data from this study showed the flexibility of triclopyr when mixed with several currently labeled HPPD- or PSII-inhibitor herbicides for bermudagrass management in sugarcane. Greater flexibility in application timing for HPPD-inhibitor herbicides when compared with PSII-inhibitor herbicides (diuron or hexazinone), and mixed with triclopyr, may provide an opportunity for sugarcane growers to suppress bermudagrass POST in April and May with minimal sugarcane injury prior to sugarcane entering the critical growth period of crop development.