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Research Article
The effect of temperature and exposure time on redroot pigweed (Amaranthus retroflexus) and yellow foxtail (Setaria pumila) seed mortality in the natural soil seed bank
- Valentina Šoštarčić, Mateja Pišonić, Laura Pismarović, Maja Šćepanović
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- Published online by Cambridge University Press:
- 08 May 2024, pp. 1-22
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Heat disinfection of soil can be used to reduce the content of the soil seed bank. However, species differ in the lethal temperature needed for seed destruction and mortality. Laboratory research was conducted on the seeds of two weed species, redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail [Setaria pumila (Poir.) Roem. et Schult]. The soil samples were collected at the experimental station Šašinovečki Lug, Zagreb (45.850289°N; 16.180465°W), Croatia and exposed to linearly increasing constant temperatures of 40, 50, 60, 80, 100 and 120 C and exposure times of 30, 60 and 90 min in a laboratory oven. Weed seeds were then extracted from the soil using the sieve separation method and survival measured by germinating seeds on the filter paper. Germination counts were converted into percentages of mortality compared to untreated seeds. The results show that both temperature and exposure time significantly affected seed mortality of both weed species. A. retroflexus shows a greater susceptibility to high temperatures than S. pumila. Fitted three-parameter sigmoid model was used to define the relationship between temperature and exposure time needed for 50% (LT50) and 90% (LT90) seed mortality. The estimated LT50 values for A. retroflexus are 58.89 – 46.08 C over the 30 to 90 min exposure times; the estimated LT90 113.36 to 65.72 C for the same durations. The estimated LT50 values for S. pumila over the 30 to 90 min exposure times ranged from 91.33 to 75.15 C; the estimated LT90 ranged from 98.79 to 90.32 C over the same durations. The research results contribute to the knowledge about the thermal sensitivity of seeds. Estimating efficacy of soil heating treatments is essential when comparing the environmental, economic and social costs of alternatives to conventional weed control methods.
Endothall and 2,4-D Activity in Milfoil Hybrid (Myriophyllum spicatum × M. sibiricum) when Applied Alone and in Combination
- Mirella F. Ortiz, Scott J. Nissen, Franck E. Dayan
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- Published online by Cambridge University Press:
- 08 May 2024, pp. 1-16
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Eurasian watermilfoil (Myriophyllum spicatum L.) is an invasive aquatic plant that can hybridize with the native Northern watermilfoil (Myriophyllum sibiricum Kom.). These milfoil hybrids (M. spicatum × M. sibiricum) are becoming more prevalent in many lakes where the invasive and the native milfoil co-occur. Hybrid plants are more vigorous than either parent with a faster growth rate and lower sensitivity to some herbicides. The aquatic herbicides, endothall and 2,4-D, provide two effective modes of action (MOA) for management of the hybrids. For more than a decade, these two herbicides have been used in combination as an effective control option and a resistance management strategy. How this combination impacts herbicide movement and efficacy is unknown. Therefore, the objective of this research was to determine the activity of endothall and 2,4-D combined compared to activity applied alone. Absorption and translocation of endothall, 2,4-D and the combination was determined in hybrid plants over a 96-h time course. Endothall bioaccumulation was not impacted when these herbicides were applied in combination; however, 2,4-D accumulation increased by 80%, relative to when 2,4-D was applied alone. Endothall translocation from shoots to roots decreased by almost 50% when applied in combination with 2,4-D (alone = 16.7% ± 2.6; combination = 9.2% ± 1.2). Shoot-to-root translocation of 2,4-D also decreased when the two herbicides were applied in combination (24.8% ± 2.6 when applied alone to only 3.93% ± 0.4 when in the presence of endothall). This research demonstrates that combining herbicides can significantly impact herbicide activity in plants. Future research is needed to determine if this reduced translocation negatively impacts operational effectiveness when these herbicides applied in combination.
Germination attributes of metsulfuron-resistant and metsulfuron-susceptible tropical ageratum (Ageratum conyzoides) populations under various environmental conditions
- Devanshi Het Desai, Het Samir Desai, Bhagirath Singh Chauhan
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- Published online by Cambridge University Press:
- 08 May 2024, pp. 1-22
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Tropical ageratum (Ageratum conyzoides L.) is a problematic weed frequently observed in association with commercially important crops in Australian agroecosystems. Knowledge of the germination response of A. conyzoides is crucial for proactively managing this weed species, especially when herbicide resistance is involved. Herbicide screening and metsulfuron dose-response experiments were conducted on two separate populations of A. conyzoides (referred to as Sugarcane and Roadside) in an open environment to identify a metsulfuron-resistant population. Based on the survival percentage in the metsulfuron dose-response experiment, the Sugarcane population was found to be 54 times more resistant compared to the metsulfuron-susceptible population (referred to as Roadside). Subsequent laboratory experiments were performed to investigate the differential germination response of the two populations. No germination or emergence difference was observed between the Sugarcane and Roadside populations under various thermal regimes (15/5 to 35/25 C with a 12/12-hour photoperiod), salinity levels (0 to 320 mM), osmotic potentials (0 to -1.6 MPa), and burial depths (1 to 4 cm). However, different environmental conditions significantly impacted the germination and emergence of A. conyzoides. Ageratum conyzoides germinated over a wide range of temperatures, with the highest germination rate (>90%) occurring at 30/20 C. With increasing levels of salinity, osmotic potential, and burial depth, the germination/emergence of A. conyzoides declined and was completely inhibited at 300 mM salinity, -0.8 MPa osmotic potential, and a 1 cm burial depth. The data generated from this study will be useful in developing a model-based approach to predict the occurrence of this weed species and thus aid in designing ecologically sustainable integrated weed management protocols.
Resistance patterns and molecular basis to ACCase-inhibiting herbicides in Digitaria ciliaris var. chrysoblephara from China
- Qian Yang, Wei Deng, Longwei Liu, Tian Wei, Xia Yang, Jinlei Zhu, Min Lv, Yongfeng Li
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- Published online by Cambridge University Press:
- 08 May 2024, pp. 1-23
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Digitaria ciliaris var. chrysoblephara (Fig. & De Not.) R.R. Stewart is an annual xeromorphic weed that severely infests direct-seeded rice fields in China. Herbicide resistance is emerging in D. ciliaris var. chrysoblephara owing to extensive and recurrent use of acetyl-CoA carboxylase (ACCase)-inhibiting herbicide metamifop. In this study, a total of 53 D. ciliaris var. chrysoblephara populations randomly sampled from direct-seeded rice fields across Jiangsu Province were investigated for metamifop resistance and potential resistance-endowing mutations. Single-dose assays revealed that 17 (32.1%) populations evolved resistance to metamifop and 5 (9.4%) populations were in the process of developing resistance. Resistance index (RI) of metamifop-resistant populations ranged from 2.7 to 32.1. Amino acid substitutions (Ile-1781-Leu, Trp-2027-Cys/Ser, and Ile-2041-Asn) in ACCase genes were detected in resistant D. ciliaris var. chrysoblephara plants, and caused various cross-resistance patterns to ACCase-inhibiting herbicides. All of four resistant populations (YC07, YZ09, SQ03, and HA06), with different ACCase mutations, exhibited cross-resistance to the aryloxyphenoxypropionate (APP) herbicides cyhalofop-butyl (RIs, 10.0 to 19.9), fenoxaprop-P-ethyl (RIs, 53.7 to 132.8), and haloxyfop-P-methyl (RIs, 6.2 to 62.6), and the phenylpyrazoline (DEN) pinoxaden (RIs, 2.3 to 5.4), but responded differently to the cyclohexanedione (CHD) herbicides clethodim and sethoxydim. It is noteworthy that four post-emergence herbicides used for rice cropping, including bispyribac-sodium, pyraclonil, quinclorac, and anilofos, showed poor control effect against D. ciliaris var. chrysoblephara, suggesting few alternations for managing this weed in rice fields except ACCase inhibitors. In conclusion, this work demonstrated that the D. ciliaris var. chrysoblephara had developed resistance to ACCase-inhibiting herbicides in rice cultivation of China, and target-site amino acid substitutions in ACCase were primarily responsible for metamifop resistance.
Metabolism of halauxifen acid is regulated by genes located on wheat chromosome 5A
- Olivia A. Landau, Jeanaflor Crystal T. Concepcion, Dean E. Riechers
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- Published online by Cambridge University Press:
- 15 April 2024, pp. 1-20
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Allohexaploid wheat (Triticum aestivum L.) is tolerant to halauxifen-methyl (HM) via rapid detoxification of the phytotoxic form of HM, halauxifen acid (HA), to non-phytotoxic metabolites. Previous research utilizing ‘Chinese Spring’ (CS) wheat, alien substitution (i.e., endogenous chromosome pair substituted with a homoeologous pair from diploid Sear’s goatgrass (Aegilops searsii M. Feldman & M. Kislev (AS)), or nullisomic-tetrasomic (NT) lines indicated plants lacking chromosome 5A are more sensitive to HM than CS. We hypothesized the increased HM sensitivity of these plants results from losing gene(s) on chromosome 5A associated with HA metabolism, which leads to a reduced HA detoxification rate relative to CS. To compare HA abundance among AS, CS, alien substitution and NT lines during a time course, two excised leaf studies using unlabeled HM and liquid chromatography-mass spectrometry analyses were performed. Aegilops searsii accumulated more HA than CS and each substitution line at 8, 12 and 24 h after treatment (HAT). Furthermore, only the wheat substitution line lacking chromosome 5A displayed greater abundance of HA relative to CS (2.4- to 3.8-fold, depending on the time point). In contrast, HA abundances in lines possessing chromosome 5A were comparable to CS at all points. When comparing NT lines to CS, the nullisomic 5D-tetrasomic 5A (N5D-T5A) line displayed similar HA abundance, whereas the nullisomic 5A-tetrasomic 5D (N5A-T5D) accumulated approximately three-fold more HA at 12 and 24 HAT. These results biochemically support the hypothesis that genes encoding HA-detoxifying enzyme(s) are located on wheat chromosome 5A and corroborate findings from previous greenhouse phenotypic experiments. Future experimentation is needed to identify and characterize genes and enzymes on wheat chromosome 5A involved with HA detoxification, which may include cytochrome P450 monooxygenases, unknown oxidases, UDP-dependent glucosyltransferases, or potentially transcription factors that regulate expression of these genes associated with HA detoxification.
Confirmation of a four-way herbicide-resistant Palmer amaranth (Amaranthus palmeri) population in Iowa
- Ryan C Hamberg, Ramawatar Yadav, Robert Hartzler, Micheal DK Owen
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- Published online by Cambridge University Press:
- 18 March 2024, pp. 1-26
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Palmer amaranth (Amaranthus palmeri S. Watson) was first reported in Iowa in 2013 and has continued to spread across the state over the last decade. Importantly, A. palmeri is widely recognized as one of the more economically important weeds in production agriculture. The presence of A. palmeri in Iowa is concerning as the species has evolved resistance to nine herbicide sites of action, however, no formal characterization has been conducted on Iowa populations. Therefore, herbicide assays were conducted on an A. palmeri population collected in Harrison County, Iowa in 2023 (Southwest Palmer Amaranth, SWPA) and a known herbicide-susceptible population collected from Nebraska in 2001 (Palmer Amaranth Susceptible, PAS). The two populations were treated with preemergence and postemergence herbicides commonly used in Iowa. The treatments included preemergence applications of atrazine, metribuzin, and mesotrione and postemergence applications of atrazine, imazethapyr, glyphosate, lactofen, mesotrione, glufosinate, 2,4-D and dicamba at 1x and 4x the labeled rates. Survival frequency of SWPA was >90% when treated postemergence with 1x rates of imazethapyr, atrazine, glyphosate, and mesotrione compared to ≤6% for PAS. Both SWPA and PAS had 0% survival when treated with lactofen, glufosinate, 2,4-D, and dicamba at the 1x or 4x rates. Plant population density reduction for SWPA was 53% and 40% in response to 1x rates of preemergence-applied mesotrione and atrazine, respectively. Metribuzin applied preemergence reduced SWPA plant population density by >90% at both rates. Dose-response experiments revealed the 50% effective doses (ED50) of mesotrione, glyphosate, imazethapyr, and atrazine for SWPA were 9.5-,8.5-, 71- and 40-fold greater than for PAS, respectively. The results confirm that SWPA is four-way multiple herbicide-resistant. Amaranthus palmeri infestations are likely to continue to spread within Iowa, therefore diversified weed management programs that include early detection, rapid response, and effective multi-tactic management strategies will be required for control.