Pre-emergence herbicides affect seedling emergence of tropical forest tree species

Testing techniques to reduce weed infestation is a crucial step in developing direct tree seeding systems. The use of pre-emergence herbicides may be an alternative to manual weeding techniques, but so far, information on how they affect the seeds of native tree species is scarce. We established a greenhouse experiment to evaluate the effects of four pre-emergence herbicides (atrazine, diuron, isoxaflutole and oxyfluorfen) on weed suppression and seedling emergence and early growth of seven tropical forest tree species (Annona coriacea Mart., Citharexylum myrianthum Cham., Cordia ecalyculata Vell., Peltophorum dubium (Spreng.) Taub., Psidium guajava L., Pterogyne nitens Tul. and Schinus terebinthifolia Raddi). The experimental design was a randomized complete block design with five treatments and five replicates. The treatments consisted of a single dose of each pre-emergence herbicide and a control. Throughout the 60 days after sowing we evaluated weed cover and seedling emergence and early growth of tree species. Overall, our results suggest that all tested herbicides reduced weed cover; however, they also negatively affected tree species seedling emergence. Of the four herbicides tested, atrazine and diuron showed the greatest effects on tree seedling emergence, oxyfluorfen was least aggressive towards native species and isoxaflutole was most effective in weed control. Native tree species varied in their responses to herbicides, indicating that future experiments should increase the number of species tested as well as investigate how seed traits can affect the species responses to different herbicides.

Application of pre-emergence herbicides in poplar nursery production

In addition to pests and diseases, weeds are a major problem in poplar nursery production. The possibilities of herbicide application in juvenile poplar growth were researched, taking into account that weeds are one of the main limiting factors. The following pre-emergence herbicides were tested： acetochlor, S-metolachlor, metribuzin,oxifluorfen, and dimethenamid during two vegetation seasons at two locations, which differed by the soil physicochemical characteristics. The study results show that the number of weeds on sample plots was significantly reduced by the tested herbicides when compared to control plots. The highest reduction in the number of weeds was achieved using the herbicides acetochlor and metribuzin. However, metribuzin showed a phytotoxic effect on sandy soil. Metribuzin application is recommended only on the soils with higher contents of organic matter, where the phytotoxic effect was absent. Acetochlor, S-metolachlor, oxifluorfen, and dimethenamid were not phytotoxic to poplars and can be used for weed suppression in the production of poplar plants.

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?

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.

Effects of a glyphosate-based herbicide on the oestrous cycle of rats

Objective:To determine the effects of a glyphosate-based herbicide on the oestrous cycle of rats.Methods:Fifteen adult Wistar rats were randomly divided into three groups.Group A served as the control group,while groups B and C received 250 and 500 mg/kg of glyphosate-based herbicide orally for five oestrous cycles,respectively.Stages of oestrous cycle,oestrous cycle index,length of cycle,oestrous cycle ratio,serum estradiol and progesterone levels were determined.Results:The proestrus and oestrus stages of the glyphosate-based herbicide groups increased significantly(P<0.05),although proestrus in group C was not significantly different from the control group.There was a significant decrease in the metestrus and diestrus of the glyphosate-based herbicide groups(P<0.05).The oestrous cycle index of the glyphosate-based herbicide treated groups was altered;this was characterized by an increase in the oestrous index and a decrease in the metestrus and diestrus indexes.The proestrus index of group B increased,while that of group C decreased.The length of the cycle of the glyphosate-based herbicide groups significantly decreased from the 1st and 3rd week till the end of the study in groups B and C,respectively(P<0.05).There was a significant increase in the oestrous cycle ratio of the glyphosate-based herbicide groups compared to the control group(P<0.05).Though the estradiol and progesterone levels of the glyphosate-based herbicide groups increased and decreased,respectively,they were not significantly different from the control group.Conclusions:Glyphosate-based herbicide at the doses of 250 and 500 mg/kg can alter the pattern of the oestrous cycle in rats.

Effects of Different Herbicides on Weed Control in Alfalfa Field

[Objectives]The paper was to systematically study the technology of weed control in alfalfa field.[Methods]Reviving alfalfa field and newly sown alfalfa field after emergence were selected,and the effects of different herbicides on weed control and alfalfa yield were discussed.[Results]The optimal herbicides after alfalfa reviving were 5%imazethapyr and 10%imazethapyr,and the optimal dosages were 1.5 and 1.05 L/hm 2,respectively.The optimal herbicides after emergence of newly born alfalfa were 5%imazethapyr and 10%imazethapyr,and the optimal dosages were 1.5 and 0.75 L/hm 2,respectively.[Conclusions]This study will provide a technical support for high quality production of alfalfa.

Pyramiding of multiple genes generates rapeseed introgression lines with clubroot and herbicide resistance, high oleic acid content, and early maturity

Clubroot and herbicide resistance,high oleic acid(OA)content,and early maturity are targets of rapeseed(Brassica napus L.)breeding.The objective of this study was to develop new male-fertility restorer lines by pyramiding favorable genes to improve these traits simultaneously.Seven elite alleles for the four traits were introduced into the restorer line 621R by speed breeding with marker-assisted and phenotypic selection.Six introgression lines(ILs)were developed with four-to seven-gene combinations and crossed with two elite parents to develop hybrids.All ILs and their corresponding hybrids displayed high resistance to both clubroot pathotype 4 and sulfonylurea herbicides.Three ILs and their hybrids showed large increases in OA contents and four showed earlier maturity.These new ILs may be useful in rapeseed hybrid breeding for the target traits.

A nonsynonymous mutation in an acetolactate synthase gene (Gh_D10G1253) is required for tolerance to imidazolinone herbicides in cotton

Background Herbicide tolerance in crops enables them to survive when lethal doses of herbicides are applied to surrounding weeds.Herbicide-tolerant crops can be developed through transgenic approaches or traditional mutagenesis approaches.At present,no transgenic herbicide tolerant cotton have been commercialized in China due to the genetically-modified organism(GMO)regulation law.We aim to develop a non-transgenic herbicide-tolerant cotton through ethyl methanesulfonate(EMS)mutagenesis,offering an alternative choice for weed management.Results Seeds of an elite cotton cultivar Lumianyan 37(Lu37)were treated with EMS,and a mutant Lu37-1 showed strong tolerance to imidazolinone(IMI)herbicides was identified.A novel nonsynonymous substitution mutation Ser642Asn at acetolactate synthase(ALS)(Gh_D10G1253)in Lu37-1 mutant line was found to be the potential cause to the IMI herbicides tolerance in cotton.The Ser642Asn mutation in ALS did not present among the genomes of natural Gossypium species.Cleaved amplified polymorphic sequence(CAPS)markers were developed to identify the ALS mutant allele.The Arabidopsis overexpressing the mutanted ALS also showed high tolerance to IMI herbicides.Conclusion The nonsynonymous substitution mutation Ser642Asn of the ALS gene Gh_D10G1253 is a novel identi-fied mutation in cotton.This substitution mutation has also been identified in the orthologous ALS genes in other crops.This mutant ALS allele can be used to develop IMI herbicide-tolerant crops via a non-transgenic or transgenic approach.

Limiting Factors and Countermeasures for the Development of Biological Herbicides

This paper mainly analyzes the main limiting factors in the development of biological herbicides,such as narrow herbicidal spectrum,vulnerable to environmental impacts,difficulties in preparing dosage forms,difficult separation and low yield of active substances,biological safety,etc.Moreover,countermeasures and suggestions are put forward,including strengthening the study of biological screening of herbicidal activity,microbial metabolites and their use as lead compounds,dosage forms,fungi complex formulation,fungi and herbicide complex formulation,and fermentation technology.

Review and Analysis: Did the United States Transport, Off-Load and Use Commercial 2,4,5-T Herbicides with Unknown Amounts of Dioxin TCDD on Military Base Grounds in Panama Canal Zone between 1948 and 1999?

The 84 km Panama Canal connecting the Atlantic and Pacific oceans has historically been a strategic waterway for shipping and the location of United States (US) military bases. Since the construction of Lake Gatun reservoir, canal locks and navigation channel through the Isthmus of Panama tropical forests in the 1910s, chemicals, pesticides, and herbicides have been essential for controlling upland and wetland vegetation as well as managing mosquito-borne diseases. Chemicals and pesticides flowed into Lake Gatun via land surface runoff and subsurface drainage either attached to the sediment or in solution during the rainy season. Lake Gatun and the Panama Canal was the drinking water source for most of the civilian and military population living in the Panama Canal Zone. Between 1948 and 1999, US military base commanders had the ability to order, from the Federal Supply Catalog, commercially available herbicide 2,4,5-T with unknown amounts of dioxin TCDD for use on the military base grounds in the Panama Canal Zone. The herbicide 2,4,5-T was transported to Panama Canal Zone ports, including the ports Cristobal on the Caribbean and Balboa on the Pacific, and distributed to the US military bases in Panama by rail or truck. The US National Toxicology Program and the International Agency for the Research on Cancer listed dioxin and TCDD as known human carcinogens. Dioxins are endocrine disrupters and can cause certain chloracne, cancers, developmental and reproductive effects. In 1985, the United States government banned the manufacture of the herbicide 2,4,5-T, with unknown amounts of dioxin TCDD, after it was shown to cause cancer in animals. The objectives of this study are to determine: 1) the fate of dioxin TCDD, a contaminant in the herbicide 2,4,5-T, sprayed on the US military base vegetation in the Panama Canal Zone from 1948 to 1999, 2) the transport of dioxin TCDD rich sediment via soil erosion and overland flow into Lake Gatun and Panama Canal waterways and 3) the human health impacts of dioxin TCDD, a known carcinogen, on US military and Panamanian civilians exposed to dioxin TCDD in the Panama Canal Zone.

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.

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%.

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.

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.