Tetflupyrolimet treatments had complete or near complete control of Echinochloa spp. by 14 DAT, but by 56 DAT, complete control was observed in all treatments regardless of tetflupyrolimet application timing. The grower standard treatment had near complete control of bearded sprangletop at 14 DAT, which later increased to complete control by 56 DAT. Treatments including both PRE and POST applications of tetflupyrolimet had season long complete control of bearded sprangletop. Excellent grass control by tetflupyrolimet is consistent even when combined with other herbicides with or without activity on grasses. Mixing tetflupyrolimet with grass control herbicides does not appear to provide an antagonistic effect on weed control unlike the combination of other rice herbicides, such propanil tank mixed with ACCase inhibitors that was reported by Matzebacher et al. . Because tetflupyrolimet has activity on grasses with no activity on sedge or broadleaf weeds, a combination of tetflupyrolimet with other herbicides that control sedge and broad leaf weeds is required for complete control of the weed species that are common in California rice fields. In 2022, the grower standard treatment showed season long complete control of rice field bulrush . All other treatments showed complete control of rice field bulrush at 14 DAT, which then decreased by 56 DAT to 88 to 97% control in treatments that did not include benzobicyclon plus halosulfuron, vertical grow racks which is an herbicide treatment with known activity on rice field bulrush .
The control of small flower umbrellas edge was similar to results of rice field bulrush control where complete control was obtained by the grower standard and all other treatments at 14 DAT, followed by a minimal decrease in control by 56 DAT for tetflupyrolimet followed by carfentrazone, tetflupyrolimet followed by bensulfuron followed bypropanil, tetflupyrolimet followed by triclopyr plus propanil, and clomazone followed by tetflupyrolimet followed by propanil. The only significantly different treatment for small flower umbrellas edge control was tetflupyrolimet followed by carfentrazone, which still had 72% control of small flower umbrellas edge. The lessened control of small flower umbrellas edge for this treatment is unlikely to be from herbicide resistance because previous greenhouse trials reported that this species did not show resistance to carfentrazone . Complete season long control of duck salad was achieved by the grower standard treatment as well as all other treatments besides tetflupyrolimet followed by carfentrazone, which showed 90% control at 56 DAT. Control of redstem by the grower standard treatment shifted from complete control at 14 DAT to near complete control by 56 DAT. All other treatments not including benzobicyclon plus halosulfuron had complete season long control of redstem. PRE tetflupyrolimet followed by POST benzobicyclon plus halosulfuron had moderate control of redstem at 82%, while PRE benzobicyclon plus halosulfuron followed by POST tetflupyrolimet had minimal control of redstem at 33%. Redstem is known to emerge later in the season, missing the PRE applications . The delayed emergence explains why greater control is achieved when benzobicyclon plus halosulfuron is applied POST rather than PRE, since it has slight control of this species while tetflupyrolimet has no control of redstem. Therefore, herbicides, such as propanil and triclopyr, are needed to successfully control redstem.
In 2023, control of ricefield bulrush by the grower standard at 14 DAT was 98% and 100% at 56 DAT . There was a wide range of 40 to 100% control of ricefield bulrush for all other treatments. Ricefield bulrush control was 65, 50, and 40% with tetflupyrolimet followed by triclopyr and propanil, clomazone followed by tetflupyrolimet followed by propanil,and tetflupyrolimet followed by benzobicyclon plus halosulfuron, respectively. The low rice field bulrush control by these treatments was largely because none of the PRE herbicides in these treatments have good activity on sedges . Furthermore, the 14 DAT rating was only 2 to 3 days after the follow up herbicide application which was not enough time to completely control ricefield bulrush. By 56 DAT, near complete or complete control was observed in all treatments except tetflupyrolimet followed by carfentrazone, which gave 77% control. In 2023, small flower umbrellas edge control by the grower standard increased from 96% control at 14 DAT to complete control by 56 DAT. All other treatments showed either near complete or complete control of small flower umbrellas edge throughout the season. The grower standard showed complete control of duck salad throughout the entire season. In all the other treatments, there was complete control of duck salad at 14 DAT besides tetflupyrolimet followed by triclopyr and clomazone followed by tetflupyrolimet followed by propanil . This varying control is once again because of the application timings, where the PRE herbicides do not have activity on duck salad but by 56 DAT, an application of propanil or triclopyr has been made. Near complete control was shown at 56 DAT in all treatments excluding tetflupyrolimet followed by carfentrazone, which was significantly lower from most other treatments at 83%. The grower standard treatment showed no control of redstem at 14 DAT due to the weak activity of benzobicyclon plus halosulfuron on redstem , however by 56 DAT, redstem was completely controlled by the subsequent propanil and triclopyr applications. All other treatments had complete control of redstem at 14 DAT.
However, by 56 DAT, control of redstem in treatments that did not include an application of propanil decreased, ranging from 63 to 73%, while the treatments that did include an application of propanil achieved near complete control . The control of grass, sedge, and broad leaf weeds by the combination of herbicides used in this experiment showed acceptable control in both years without signs of synergistic or antagonistic effects. There have been a multitude of both herbicide synergism and antagonism cases in rice across the world, such as the synergism of barnyard grass and red rice control when mixing imazethapyr, propanil, and thiobencarb . This suggests that tetflupyrolimet may be more user friendly for applicators and growers than other available rice herbicides, however, it is crucial to understand the weed populations dynamics in a field when choosing herbicide programs to ensure the effective control of all weed species present. The grower standard treatment showed slight rice injury symptoms of stunting and stand reduction by 28 DAT, 4×4 plastic tray which completely recovered by 42 DAT . At 28 DAT, tetflupyrolimet followed by thiobencarb followed by propanil showed 16% injury compared to the non-treated control. Because of the ability of thiobencarb to reduce shoot growth, the application of thiobencarb could have had damaged the root system of the rice causing death of some plants that were not completely anchored to the seedbed . There was no chlorosis observed for any herbicide treatment at 14 DAT, however at 28 DAT, only three treatments – tetflupyrolimet followed by benzobicyclon plus halosulfuron, tetflupyrolimet followed by thiobencarb followed by propanil, and benzobicyclon plus halosulfuron followed by tetflupyrolimet – showed very slight chlorosis. Rice plants, however, completely recovered from chlorosis by 42 DAT. Moderate bleaching was observed in the clomazone followed by tetflupyrolimet followed by propanil treatment at 7 DAT but fully recovered by 14 DAT, which was not surprising because clomazone is known to cause bleachingof rice after its application . There were no bleaching symptoms observed in any other treatments. No significant stunting was observed at 14 DAT for any treatment. At 28 DAT, tetflupyrolimet followed by thiobencarb followed by propanil showed slight stunting symptoms of 10% . This response was not surprising because thiobencarb is known to show stunting in rice . By 42 DAT, however, the stunted rice had completely recovered. There were no significant or lasting necrosis symptoms observed in this study. The average yield for the non-treated control in 2022 was 3,687 kg ha-1 , which was significantly lower than all other treatments . The grower standard treatment yielded 9,118 kg ha-1 , which was not significantly different from any tetflupyrolimet treatment. Of the tetflupyrolimet treatments, the lowest yielding treatment was clomazone followed by tetflupyrolimet followed by propanil at 7,740 kg ha-1 and the highest yielding treatment was tetflupyrolimet followed by thiobencarb followed by propanil treatment 9,552 kg ha-1 . The reduced yield of the clomazone followed by tetflupyrolimet followed by propanil treatment could be due to early bleaching resulting from the PRE clomazone application .
The greater yield from the tetflupyrolimet followed by thiobencarb followed by propanil treatment could be from superior weed control throughout the season that caused a lower level of weed competition to rice. However, in 2023, the only significant difference detected was that the yield of the non-treated control was significantly lower than all other treatments . The difference of higher yields in 2022 and lower yields in 2023 could possibly be due to the cooler weather during the 2023 season compared to 2022 .There was significant interaction between treatment and year for necrosis and yield while there were no significant treatment by year interactions for bleaching, chlorosis, stunting, and stand reduction symptoms. Therefore, necrosis and yield data were analyzed separately by year and all other rice symptom data were combined. In general, slight chlorosis symptoms in both years were observed in the grower standard treatment for ‘CM-203,’ ‘M-206,’ and ‘M-209’ at 14 DAT but rice plants completely recovered by 28 DAT . The grower standard treatment also showed minimal stunting and stand reduction symptoms in all varieties, which fully recovered from stunting shortly thereafter. No tetflupyrolimet treatments, regardless of application timing or rate, had significant levels of chlorosis, bleaching, stunting, or stand reduction at any rating time. In 2022, consistent necrosis in the tips of the rice leaves was observed. At 14 DAT, all treatments besides PRE tetflupyrolimet at 0.125 kg ai ha-1 showed minimal necrosis, however, it does not seem to be a trend of a specific variety showing necrotic symptoms . Importantly, these necrosis symptoms also were observed in treatments that did not include tetflupyrolimet, which suggests that the necrosis symptoms were not related to application of tetflupyrolimet. These minimal symptoms persisted until the end of rice heading stage when they fully recovered before harvest. Average yield data for all tetflupyrolimet treatments were similar to the grower standard treatment within every variety . In 2023, there were no necrosis symptoms observed, which suggests that the necrosis symptoms observed in 2022 were not from tetflupyrolimet, but rather possibly abiotic factors . Furthermore, no necrosis symptoms were observed in any of the other two experiments, regardless of year or site. Genetic variations within species can contribute to differential response of herbicides, however, no varietal response to tetflupyrolimet wasobserved in this study. Rice varietal response was reported in California when clomazone and triclopyr were used . The yield data in 2023 for all tetflupyrolimet treatments were comparable to the grower standard treatment for every variety.Tetflupyrolimet provided excellent season long control of Echinochloa spp. and bearded sprangletop regardless of application timing. There was no trend of late season escapes of bearded sprangletop in tetflupyrolimet treatments unlike other bearded sprangletop control herbicides such as clomazone and thiobencarb. The introduction of tetflupyrolimet to the rice cropping system is contingent upon its ability to perform well in an herbicide program where sedge and broadleaf weeds can be controlled as well. Tetflupyrolimet applied in combination with benzobicyclon plus halosulfuron, thiobencarb followed by propanil, bensulfuron followed by propanil, triclopyr and propanil, or clomazone followed by propanil provided near perfect season long weed control. There were neither synergistic nor antagonistic effects when tetflupyrolimet was applied with any of the herbicides in this experiment. Excellent crop safety was displayed across each experiment, regardless of rate or timing. Tetflupyrolimet gave excellent grass control as both a pre-emergent and post-emergent herbicide incorporated into a weed management program, however, if tetflupyrolimet is applied later than day of seeding, a higher rate is likely needed for the same grass control results. California rice varieties – ‘M-105,’ ‘M-206,’ ‘M-209,’ ‘M-211,’ ‘L-208,’ and ‘CM-203’ – did not show any trend of crop injury caused by tetflupyrolimet. Tetflupyrolimet could be a valuable addition to weed control programs in California water seeded rice, regardless of variety grown.Understanding the evolutionary genetics of adaptation to human-mediated practices like small and large-scale production agriculture is critical to address global challenges including the security of food, fuel, bio-product, and fiber production.