Control of Glyphosate-Resistant Giant Ragweed (<i>Ambrosia trifida</i>L.) with 2,4-D Followed by Pre-Emergence or Post-Emergence Herbicides in Glyphosate-Resistant Soybean (<i>Glycine max</i>L.)

Control of glyphosate-resistant giant ragweed is a challenge, particularly for soybean growers, because of limited effective post-emergence (POST) herbicide options. Many soybean growers in no-till production systems use 2,4-D in burndown application for control of broadleaf weeds, including giant ragweed. Field experiments were conducted at David City, NE, in 2012 and 2013 to evaluate 2,4-D followed by PRE or POST herbicide programs for control of glyphosate-resistant giant ragweed in glyphosate-resistant soybean. Results suggested that burndown application of 2,4-D or saflufenacil plus imazethapyr resulted in 89 to 99% control of giant ragweed at 21 days after treatment. Burndown-only treatments of S-metolachlor plus metribuzin or sulfentrazone plus cloransulam resulted in poor control (≤65%) of giant ragweed and reduced soybean yield (≤ 577 kg&middotha-1). Burndown application of 2,4-D followed by saflufenacil plus imazethapyr, S-metolachlor plus metribuzin, or sulfentrazone plus cloransulam applied pre-emergence (PRE) or cloransulam, chlorimuron, fomesafen, imazethapyr, or lactofen in tank-mixtures with acetochlor applied POST resulted in 87% to 99% giant ragweed control, reduced density to ≤7 plants m-2, and resulted in soybean yield from 2519 to 3823 kg&middotha-1. There was no difference among and between 2,4-D followed by PRE or POST herbicides for giant ragweed control, density, or soybean yield, indicating all the two pass herbicide programs were effective. It is concluded that glyphosate-resistant giant ragweed can be effectively controlled in soybean by including 2,4-D in burndown program followed by PRE or POST herbicides tested in this study.

Precipitation Influences Pre- and Post-Emergence Herbicide Efficacy in Corn

Selecting a preemergence (PRE) and postemergence (POST) herbicide program that has the greatest efficacy can be difficult for corn producers and is highly dependent on weed spectrum. Weather conditions before and after herbicide application can further complicate decisions because they influence herbicide efficacy. Eleven field trials were conducted at three locations in Southwestern Ontario from 2003 to 2006, to determine the most effective PRE and POST corn herbicides for weed control. The most abundant weed species across all locations were redroot pigweed (Amaranthus retroflexus L.), common ragweed (Ambrosia artemisiifolia L.), common lambsquarters (Chenopodium album L.), and green foxtail (Setaria viridis (L.) Beauv.). Nine PRE herbicide treatments and eleven POST (applied at the 3-4 leaf stage of corn) herbicide treatments were tested. Results from this study suggest that the timing and amount of precipitation influence herbicide efficacy. For example, precipitation levels 0-17 mm within seven days after herbicide application (PRE or POST) provided unacceptable weed control in treatments that included atrazine, dimethenamidp, isoxa-flutole/atrazine or S-metolachlor/benoxacor. Cumulative precipitation during the 14 days after PRE application that exceeded the monthly average (by at least 64%) reduced Setaria viridis control with pendimethalin. This study demonstrates that a better understanding of how environmental conditions, especially precipitation affect herbicide efficacy, need to be considered by growers when selecting a corn herbicide program to reduce the possibility of weed control failure.

Evaluation of Pre-Emergence and Post-Emergence Herbicides for Weed Management in Miscanthus sacchariflorus and Miscanthus sinensis

Miscanthus,is a promising bioenergy crop,considered superior to other bioenergy crops because of its higher water and nutrient use efficiency,cold tolerance,and higher production of biomass.Broadleaf weeds and grass weeds,cause major problems in the Miscanthus field.A field experiment was conducted in 2018 and 2019,to assess the effects of pre-emergence(alachlor and napropamide)and post-emergence herbicides(nicosulfuron,dicamba,bentazon,and glufosinate ammonium)on broadleaf and grass weeds in M.sinensis and M.sacchariflorus fields.The weed control efficiency and phytotoxicity of pre-and post-emergence herbicides were evaluated at 30 days after treatment(DAT)and compared to those of the control plots.The results showed wide variations in the susceptibility of the weed species to the treated herbicides.Treatment with nicosulfuron 40 g.a.i.ha^(-1) provided the most effective overall weed control(with 10%visual injury),without affecting the height and biomass of neither Miscanthus species in the field.Post-emergence herbicides such as glufosinate ammonium 400 g.a.i.ha^(-1) and dicamba 482 g.a.i.ha^(-1) were effective and inhibited the growth and density of the majority of weeds to a 100%;however,they showed significant phytotoxicity(toxicity scale of 1-10)to both species of Miscanthus.The application of glufosinate ammonium caused severe injuries to the foliar region(90%visual injury)of both Miscanthus sps.Comparatively,M.sinensis showed a slightly higher tolerance to the herbicides nicosulfuron,bentazon and napropamide with 10%visual injury at the recommended dose than M.sacchariflorus.The present study clearly showed that infestation of broadleaf and grass weeds in Miscanthus fields can cause significant damage to the growth and biomass of Miscanthus and applying pre-emergence and post-emergence herbicides effectively controls the high infestation of these weeds.

Review and Analysis: Evaluation of the Impacts and Consequences of Using Agricultural Herbicides as Military Chemical Weapons in Second Indochina War

The legacy of the human misery caused by the application of the herbicides including Agent Purple and Agent Orange contaminated with unknown amounts of dioxin TCDD and Agent Blue, the arsenic-based herbicide, sprayed over the jungles, rice fields, and hamlets of Vietnam is still haunting us today. Why did this happen? Could it have been prevented? Was it necessary United States military strategy? Was it an intentional decision to inflict this blight on the enemy soldiers and the Vietnamese, Cambodian, and Laotian civilians, to poison their land and cause generations of harm? Alternatively, was it an unpreventable accident in the march of military history? What patterns in the U.S. government’s thought process could be identified as the cause, which led to the decision to use these herbicides as tactical chemical weapons? If the introduction of herbicide (chemical) weapons had not been made, would the outcome of the Vietnam War and the Secret Wars in Laos and Cambodia have been any different? The objective of this treatise is to outline the role of world events and backgrounds and the role of the leaders, U.S. military, CIA, USDA, U.S. State Department, the U.S. President appointed Ambassadors to Vietnam and Laos, chemical companies, and President Diệm’s Republic of Vietnam (RVN) government and military. Their collective advice led to the decision to use herbicides as military and environmental chemical weapons in the Second Indochina War. Were the National interests achieved by U.S. military strategy in the RVN using herbicide weapons worth the long-term environmental and human health consequences in Vietnam, Cambodia, and Laos? Did it impact the outcome of the Second Indochina War?

Research Progress on Plant Source Herbicide Adjuvants

As the important components of pesticide adjuvants, vegetable oil and its derivative adjuvants will be the focus of future development of herbicide adjuvants due to their superiority in good affinity with plants, strong biological degradability, few risk of damage, environrnental safety and ability to improve the weed control efficient. The research progress and application status of the plant source herbicide adjuvants were summarized, as well as the weeding enhancement mechanism and the effects on the environment and non-target organisms, and the existing problems and development trends were reviewed.

An Overview of Research on Microbial Herbicide

The development of microbial herbicide for weed control has been serious- ly regarded all over the world and has made rapid progress in recent years. This paper presents a comprehensive review on domestic and abroad research progress of microbial herbicide and mainly introduces the microbial herbicide products and mi- crobial sources with commercialization potential, and then proposes an outlook for their development tendency and application prospect.

Chemical Control of Herbicide Monosulfuron Plus Propazine 44% WP against Weeds in Millet Fields and Study on Factors Influencing Yield of Millet

[Objective] The paper was to resolve the poor efficacy or phytotoxicity problems in promotion of herbicide monosulfuron plus propazine 44% WP. [Method] Using orthogonal test and Duncan＇s new multiple range statistical analysis with four factors four levels and three factors two levels, the effects of factors such as herbi- cide dose, irrigation water volume, quality of soil preparation and soil moisture content on chemical control of monosulfuron plus propazine 44% WP against weeds and millet yield were compared in the test. [Result] Seven factors all had great impact on control effect of monosulfuron plus propazine 44% WP against weeds, of which her- bicide dose, irrigation water volume, quality of soil preparation and soil moisture content were the most important factors affecting millet yield. According to millet yield and economic benefit, the optimal scheme to ensure safe, efficient and economic control of monosulfuron plus propazine 44% WP against weeds was as follows： the dose of monosulfuron plus propazine 44% WP was 1 800 g/hm2, the soil was treat- ed after sowing and before seedling emergence; the soil should be smooth and sol- id; the soil moisture should reach 15%; the fields should not be irrigated after herbi- cide application, and the damage of weeds in millet fields could be effectively con- trolled within 45 d during high efficacy duration, especially the damage of dicotyledonous weeds. [Conclusion] The study provided useful information for comprehensive technology of weeds control and ensuring high yield and good harvest of millet.

Control Effects of 3 Kinds of Herbicides against Weeds in Dogbane (Apocynum venetum) Field

[ Objective] The paper was to explore the control effects of 3 kinds of herbicides against weeds in dogbane （Apocynum venetum） field. [ Method ] Using haloxyfop-R-mithyl and quizalofop-ethyl EC specifically killing monagenns gramineous weeds and chipton specifically killing dicotyledonous broad-leaf weeds, the control test against weeds in 2-year-old dogbane field was carried out. [ Result ] Haloxyfop-R-mithyl had good control effect against gramincous weeds, and its control effect against both barnyard weed （ Echinochloa crusgalli） and green bristleweed （ Setaria viridis ） was greater than 35.0% ; the control effects of quizalofop- ethyl EC against barnyard weed and green bristleweed were 14.8% and 28.6%, respectively; chipt0n had good control effect against Chenopodium album, and the control effect reached 30.8%. Moreover, 3 herbicides did not cause damage to dogbane. [ Conclusion] The study provide theoretical basis for completing cultivation technique of dogbane.

Control Effect Evaluation of Herbicides for Malignant Weed Nut Grass in Sugarcane Field

In order to screen herbicides with ideal safety characteristics to control malignant weed nut grass in sugarcane field, 20% thifensulfuron methyl WP and 65% MCPA·ametryne·diuron WP were selected for the field efficacy trial. The results showed that 20% thifensulfuron methyl WP and 65% MCPA·ametryne·diuron WP had good control effect on nut grass. The optimum dosage of 20% thifensulfuron methyl WP and 65% MCPA.ametryne-diuron WP was 1 125 g/hm^2 （effective ingredients 225 g） and 3 150 g/hm^2 （effective ingredients 2 047.5 g）, respectively. These two herbicides should be dissolved in 675 kg water per hectare and applied in the vigorous growth period of nut grass （height 10-15 cm） with oriented stem leaf spraying. The control effect after 15 days could be above 87.9%.

Research Status of Amide Herbicides and Their Safeners

The widespread use of chemical herbicides especially amide herbicides has promoted the innovation of chemical weeding in farmland, but amide herbicides have brought invisible chemical injuries to crops in addition to weeding. Herbi-cidesafeners should be applied at the same time with herbicides to ensure herbi- cides will not injure crops while controlling weeds. The research and application of safeners is of great significance to resolving or alleviating the negative effects of herbicides on crop growth. The overview, mechanism, applied research progress and existing problems of amide herbicides and their safenars are summarized.

Effect of Two Herbicides on the Growth of Early Seedlings of Rye(Secale cereale)

[Objective]The aim was to study the effect of herbicide on the growth of early seedlings of rye（Secale cereale）.[Method]Effect of two kinds of herbicide（Atrazine and APM）on seedling growth of rye was investigated at the physiological,biochemical and cellular level.[Result]The Atrazin significantly decreased the contents of chlorophyll a,b and soluble proteins.Rye seeds were treated with 0.01-1 mg/L Atrazine for 16 h,the contents of chlorophyll a and b decreased from 1.26（a）,0.49（b）mg/g FW（control）to 1.15（a）,0.46（b）mg/g FW（0.1 mg/L）and 0.81（a）,0.33（b）mg/g FW（1.0 mg/L）.The content of soluble protein decreased with the increasing concentration of Atrazin.Atrazin had no significant influence on the cell division and chromosome structure variation.The contents of chlorophyll a,b and soluble proteins had no significantly change under the treatment of APM,but the number of chromosome structure variation such as chromosome bridge,multipolar division cells,lagging chromosome and unequal division cells increased significantly.[Conclusion]The critical concentration of Atrazine was 0.1-1.0 mg/L and 4 mg/L of APM in rye.

Characterization of a strain of Sphingobacterium sp. and its degradation to herbicide mefenacet

A bacterium(designated strain Y1) degrading acetanilide herbicide mefenacet was isolated from aerobic sludge. Based on the analyses of partial 16S rRNA gene, cellular fatty acid and BIOLOG-GN, and general physiological and biochemical characteristics, strain Y1 was identified as Sphingobacterium multivolum. Strain Y1 was able to degrade mefenacet used as sources of carbon and energy. Degradation of mefenacet was accompanied by producing the metabolites N-methylaniline and an unidentified compound with molecular weight 205, indicating a metabolic pathway of mefenacet initiated by hydrolysis of amido bond.

Inheritance and molecular characterization of resistance to AHAS- inhibiting herbicides in rapeseed

Rapeseed is a very important oil crop in China; however, its production is challenging due to the absence of effective weed management strategies. This is predominantly because of a shortage of herbicide resistance genes. Acetohydroxyacid synthase （AHAS） herbicides inhibit AHAS, a key enzyme involved in branched-chain amino acid synthesis that is required for plant growth. A rapeseed line designated M342 with AHAS herbicide resistance was developed through seed muta- genesis and was studied to assess the level and mode of inheritance of the resistance and to identify the molecular basis of resistance. M342 possessed a high level of cross-resistance to sulfonylureas （SUs） and imidazolinones （IMIs）. This resistance was due to AHAS insensitivity to these herbicides and was inherited as a dominant trait conferred by a single nuclear-encoded gene. Molecular analysis revealed the presence of a Trp574Leu mutation in M342, and an allele-specific cleaved amplified polymorphic sequence （AS-CAPS） marker was developed and cosegregated with herbicide resistance in the F2, BC1, and BC2 populations. This mutation altered the transcript levels of BnAHAS1 and BnAHAS3 in M342 compared with those in the wild type, but it did not affect the agronomic or quality traits. The simple genetic inheritance of this mutation and the availability of the cleaved amplified polymorphic sequence （CAPS） marker and herbicide resistance gene should facilitate the development of herbicide-resistant rapeseed cultivars for effective weed control in China.

Isolation and Structural Speculation of Herbicide-Active Compounds from the Metabolites of Pythium aphanidermatum

Natural herbicides, or environment-friendly bioherbicides have been attracted more and more attentions. Isolation and structural identification of natural herbicide-active compounds from plant pathogens has been proved to be an effective approach for novel lead discovery of the pesticide development. In this study, the metabolites of the mutant strain PAM1, which obtained from PA1 of Pythium aphanidermatum （Eds.） Fitzp by ultraviolet radiation were separated and identified by HPLC, NMR, and IR. The results revealed that three active compounds including 4-hydroxy-3-methoxycinnamic acid and two indole derivatives, exhibited inhibition activity on the elongation of radical and coleoptile of Digtaria sanguinalis （L.） Scop.

Effect of Cadmium and Herbicides on the Growth, Chlorophyll and Soluble Sugar Content in Rice Seedlings

To investigate the combined effects of Cd^2＋ （ 0,10,100,500 μmol/L） , acetochlor （AC） （0,1.6,4.0,8.0μmol/L）, and bensulfuronmethyl （BSM） （ 0,0.16,0.40,0.80 μmol/L） on the biomass,leaf soluble sugar, total chlorophyll （chl） content, chl a/b ratio, and Cd content in roots and shoots in the rice seedlings, pot culture experiments were conducted with rice （Oryza sativa L. ） cultivar Jinyou 402. The results showed that the Cd and AC combined treatment （Cd＋ AC treatment） significantly inhibited the growth of the roots and shoots. The root dry weight/shoot dry weight （RDW/SDW） ratio, total chlorophyll content and chl a/b ratio decreased by 41%, 50%, 56% , respectively, in comparison with the control, as well as the leaf soluble sugar content, plant dry weight /plant fresh weight （PDW/PFW） ratio increased by 284% and 44% , respectively. Cd content in the roots and shoots had a decreasing tendency with the increasing concentration of AC under the Cd＋AC treatment. The Cd and BSM combined treatment （Cd＋BSM treatment） had a similar result to the Cd＋AC treatment. The results suggest that the toxicity of Cd to rice seedlings has been enhanced due to its combination with herbicides.

Recent Advances in Development of Herbicide Resistant Transgenic Hybrid Rice in China

In addition to weed control in direct seeding field of hybrid rice, herbicide resistance genes were used by Chinese scientists to increase and identify the purity of hybrid seeds, and to realize the mechanization of hybrid seed production. The elite restorer lines, such as Minghui 63, R752, T461, R402, D68 and E32 were transformed directly with herbicide resistance genes, in which D68 and E32 are restorer lines of two-line system and the others are of three-line system. Because almost all of important restorer lines are indica varieties and are recalcitrant in transformation, many herbicide resistant near-isogenic restorer lines were developed by sexual hybridization of indica and japonica varieties and backcross with indica restorer lines later, such as Ce 64, Minghui 63, Teqing, Milyang 46, R402 and 9311, in which 9311 is a restorer line of two-line system. The elite photoperiod-sensitive/thermo-sensitive genic male sterile lines, such as Pei＇ai 64S, P88S, 4008S and 7001S, were transformed with herbicide resistance genes. A few herbicide resistant male sterile lines were developed through sexual hybridization and subsequently systemic selection, such as Bar1259S, Bar2172S, 05Z221A and 05Z227A. With the employment of herbicide resistant male sterile lines or herbicide resistant restorer lines, a few herbicide resistant hybrid rice combinations were developed, such as Xiang 125S/Bar 68-1 and Pei＇ai 64S/Bar 9311. Based on herbicide resistance, the research was marching on to investigate the parental lines of hybrid rice with insect resistance, drought tolerance, etc.

Herbicide resistance: Development of wheat production systems and current status of resistant weeds in wheat cropping systems

Herbicide resistance in crops has extended the scope of herbicide applications to control weeds. The introduction of herbicide resistant crops resulted in a major shift in the way that herbicides are used in many crops, but not necessarily increased the prevalence of herbicide use, especially in wheat. Wheat is one of the most widely grown crops in the world and currently only two major herbicide-resistant wheat groups have been commercialized to manage weeds in a cost-effective manner. However, sustainable wheat production is threatened by the expanding occurrence of herbicide-resistant weed populations with limited efforts to discover new herbicide molecules. Selective control of certain problematic weeds in wheat was impossible until development and introduction of the technologies, Clearfield and Co AXium Production Systems. However, the current limitations of reliance on specific herbicides and evolution of resistant weeds mandate precautions and considerations when using these systems to prevent the loss of existing herbicide resources and continue sustainable wheat production. The focus of this review is to provide an overview of natural pre-existing herbicide resistance and development of herbicide-resistant technologies in wheat. The mechanisms of resistance to herbicides in wheat as well as the weed populations in wheat cropping systems, and implications for weed management are discussed.

Predicting herbicides concentrations in paddy water and runoff to the river basin

This study was conducted to investigate the dissipation pattern and runoff of herbicides to the river basin from the paddy fields. Pesticide paddy field model(PADDY) was applied to predict herbicide concentration in paddy fields. A field study was conducted in a paddy farm of Higashi Hiroshima City, Hiroshima Prefecture, Japan in the year of 2003 paddy season. The herbicides were mefenacet, thiobencarb, and bensulfuron methyl. The sample water was analyzed by using gas chromatography and HPLC after solid phase extraction. Predicted dissipation rate of thiobencarb in paddy water was higher(DT_ 50 = 4 36) than that measured, with a lower k value(-0 069). Two weeks after application no thiobencarb was detected in the drainage channel and down stream. In the down stream, thiobencarb was detected until 3 d after application, with a range of 0 02% to 0 08% of applied herbicide. The predicted dissipation rate(k) and half-life(DT_ 50 ) of mefenacet was not significantly different from that of measured. In the drainage channel, upstream and downstream mefenacet was found during the whole study period. In downstream, the maximum concentration of mefenacet was present 0 61% of applied in the paddy field on 3DAH. The dissipation rate(k) of BSM varied from -0 0860 to -0 1059 to with half-life(DT_ 50 ) 3 5 and 2 84 d. In upstream water, no BSM was detected except trace amounts(0 01 μg/L) at 3 d after application. However, in the drainage channel 8%, 6% and 1 58% of applied BSM was present at 0, 1 and 3 d after application respectively. In the down stream, the highest concentration was 1 06%, shortly after application.

Development of herbicide resistance genes and their application in rice

Rice is one of the most important food crops in the world.Weeds seriously affect the rice yield and grain quality.In recent years,there are tremendous progresses in the research and application of herbicideresistant genes in rice worldwide.This article reviews the working mechanisms of six herbicides(glyphosate,glufosinate,acetolactate synthase inhibitor herbicides,acetyl-Co A carboxylase inhibitor herbicides,hydroxyhenylpyruvate dioxygenase(HPPD)inhibitor herbicides and dinitroaniline herbicides),the resistance mutations of the corresponding herbicide-target genes,and the herbicide detoxification mechanisms by non-target genes.Examples are provided on herbicide-resistant rice materials obtained by transformation of exogenous resistance genes,by artificial mutagenesis and mutant screening,and by modifying the target genes through gene editing.This paper also introduces the current application of herbicide-resistant rice,points out problems that may be caused by utilization of herbicide resistant rice and solutions to the problems,and discusses the future prospects for the development of herbicideresistant rice.

Phytotoxicity of four herbicides on Ceratophyllum demersum,Vallisneria natans and Elodea nuttallii

The physiological effects of 4 herbicides （butachlor, quinclorac, bensulfuron-methyl and atrazine） on 3 submerged macrophytes （Ceratophyllum demersum, Vallisneria natans and Elodea nuttallii） were tested in laboratory. The variables of the relative growth rate and the photosynthetic pigment content showed that all of the tested herbicides affected the growth of the plants obviously, even at the lowest concentration （0.0001 mg/L）. Except for the C. demersum treated with quinclorac at 0.005 and 0.01 mg/L, the relative growth rates of the plants were inhibited significantly （p 〈 0.01）. Statistical analysis of chlorophyll a （Chl-a） contents was carded out with both the t-test and one-way ANOVA to determine the difference between the treatment and control. The results showed that Chl-a contents of the plants in all treatment groups were affected by herbicides significantly, except for the C. demersum treated with bensulfuron-methyl at 0.0005 mg/L. The decrease in Chl-a content was positively correlated to the dosage of the herbicides in most treatment groups. It was suggested that herbicides in water bodies might potentially affect the growth of aquatic macrophytes. Since the Chl-a content of submerged macrophytes responded to the stress of herbicides sensitively and directly, it could be used as a biomaker in environmental monitoring or in the ecological risk assessment of herbicide contamination.