Pre-emergence Herbicidal Activity Research Articles

Screening of 1, 2, 4-triazole imines for pre-emergence herbicidal activity in wheat

Screening of 1, 2, 4-triazole imines for pre-emergence herbicidal activity in wheat

Design, synthesis and evaluation of novel cis-p-menthane type Schiff base compounds as effective herbicides

p-Menthane type monoterpene derivatives were identified as bio-based compounds with high herbicidal activities. In order to search novel p-menthane type monoterpene derivatives in good performance, a series of novel cis-p-menthane type Schiff base derivatives were designed and synthesized. All target products were easily available novel compounds and characterized by FT-IR, 1H NMR, 13C NMR and ESI+-MS. Their pre-emergence herbicidal activities against annual ryegrass were evaluated. The bioassays indicated that most of the target compounds displayed excellent herbicidal activities in pre-emergence treatment.

An efficient synthesis method targeted to a novel aziridine derivative of p-menthane from turpentine and its herbicidal activity

A novel aziridine compound N-acetyl-1,2-azacyclo-p-menthane d was synthesised using turpentine as raw material and characterised by FT-IR, 1H NMR, 13C NMR, ESI+-MS and HRMS. The pre-emergence herbicidal activities of d and its synthetic intermediates cis- and trans-N,N′-diacetyl-p-menthane-1,8-diamine (b2 and b1) were determined. The result showed that d exhibited much higher herbicidal activities against annual ryegrass, Digitaria sanguinalis and Ixeris denticulate than b2 and b1. The IC50 of d against the root and shoot growth of these three plants were lower than 1 mmol L−1. In contrast, the IC50 of b1 and b2 against the root and shoot growth of these plants were more than 10 mmol L−1.

Synthesis and Herbicidal Activities of p-Menth-3-en-1-amine and Its Schiff Base Derivatives.

p-Menth-3-en-1-amine, 4, and its Schiff base derivatives, 5a-l, were designed and synthesized. They were characterized by FT-IR, ESI+-MS, HRMS, 1H NMR, and 13C NMR spectral analyses, and their pre-emergence herbicidal activities against ryegrass were evaluated. All of the compounds showed excellent herbicidal activity. The Schiff bases showed stronger herbicidal activities than the original amine 4. These compounds showed herbicidal activities comparable to that of glyphosate. The herbicidal activities of 5k and 5l against ryegrass shoot growth were 78.3 and 355.6% higher than that of glyphosate, respectively. Furthermore, the introduction of a chlorine or bromine atom into the Schiff base derivatives containing a furan or benzene ring was beneficial to increase the activity. However, the herbicidal activities were not clearly affected when the heteroatom of the five-membered heterocyclic Schiff base or the position of the substituent on pyridine Schiff base was altered.

Synthesis and herbicidal activity of 3-{[(hetero)aryl]methanesulfonyl}-4,5-dihydro-1,2-oxazole derivative; Discovery of the novel pre-emergence herbicide pyroxasulfone.

Thiocarbamate sulfoxides, which are the active forms of thiocarbamate herbicides, are quickly conjugated with glutathione and decomposed in soil. To achieve more potent and stable herbicidal activity, we previously developed a 5-{[(2,6-difluorophenyl)methoxy]methyl}-5-methyl derivative, which has a 4,5-dihydro-1,2-oxazole ring in place of the thiocarbamate to prevent conjugation and decomposition. Although the derivative showed pre-emergence herbicidal activity under flooded conditions, it displayed no herbicidal activity under upland conditions. In contrast, a 5-(methoxymethyl)-5-methyl derivative showed pre-emergence herbicidal activity against grass weeds under upland conditions. The aim of this study was to obtain a more potent compound with improved physicochemical properties for use as a pre-emergence upland herbicide via the structural optimization of a 3-{[(hetero)aryl]methanesulfonyl}-4,5-dihydro-1,2-oxazole as the core structure. In this way, we have developed the pre-emergence herbicide 3-{[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methanesulfonyl}-5,5-dimethyl-4,5-dihydro-1,2-oxazole, which has been named "pyroxasulfone." This novel compound displayed excellent herbicidal activity against grass and broadleaf weeds under upland conditions with no phytotoxicity against crops.

Biochar Decreases Atrazine and Pendimethalin Preemergence Herbicidal Activity

Biochar and vinasse are by-products of biofuel production that can be used as soil amendments. However, their addition to the soil might affect PRE herbicide activity. Although studies have shown that biochar has a high herbicide adsorption capacity, there is little information available about biochar effect on weed control especially under field conditions. Therefore, the objective of this study was to determine the influence of biochar and vinasse application on atrazine and pendimethalin availability and herbicide activity underin vitroand field conditions.In vitroatrazine and pendimethalin herbicidal activities were not influenced by vinasse addition, but biochar application reduced atrazine and pendimethalin injury for all evaluated species. A sorption experiment confirmed high affinity of biochar for atrazine and pendimethalin. Linear regression analysis showed that the slope for atrazine and pendimethalin adsorption was 16 and 4 times higher in soil with biochar than in soil alone. Under field conditions, biochar at 0.5 kg m−2reduced atrazine and pendimethalin weed control 75% and 60%, respectively. These results suggested that the use of biochar as a soil amendment in cropping system could decrease PRE herbicide efficacy. Therefore, mitigating practices such as the use of higher rates or reliance on POST herbicides and cultivation might be necessary to ensure proper weed control.

Post-emergent herbicidal activity of cineole derivatives

Essential oils are being investigated as potential herbicides or to provide leads to new environmentally and socially acceptable herbicides. Novel hydroxy and ester derivatives of 1,8-cineole and 1,4-cineole were synthesised, by chemical and biological methods, and have shown pre-emergence herbicidal activity against annual ryegrass and radish. Effects on post-emergence activity of these derivatives, as well as 1,8-cineole, eucalyptus oil and the carboxylic acids from which the esters were derived, against annual ryegrass and radish, are reported here. Results suggest that reduced root and shoot growth observed in pre-emergence herbicidal bioassays were due to post-emergence activity rather than delayed germination. All tested substances had a dose-dependent, post-emergence herbicidal activity against annual ryegrass and radish with many derivatives showing improved activity relative to 1,8-cineole and high-cineole eucalyptus oil. However, results do not support the postulate that cineole esters would be more active than their respective carboxylic acid and the hydroxy cineole. Phytotoxicity of ester derivatives may be due to metabolic cleavage of the esters to the hydroxy cineole and carboxylic acid within the plant.

Synthesis and herbicidal activities of potassium methyl 1-(substituted phenoxyacetoxy)alkylphosphonate

A series of potassium methyl 1-(substituted phenoxyacetoxy)alkylphosphonates(9a–9o) was designed and synthesized. The results of preliminary bioassays indicate that most of the title compounds possess excellent pre-emergence and post-emergence herbicidal activities against Brassica napus, Amaranthus mangostanus, Medicago sativa, Echinochloa crusgalli, and Digitaria sanguinalis at a dosage of 1500 g/ha(1 ha=10000 m2). Especially, potassium methyl 1-(2,4-dichlorophenoxyacetoxy)-1-(4-methylphenyl)methylphosphonate(9g) and potassium methyl 1-(2,4-dichlorophenoxyacetoxy)-1-(furan-2-yl)methylphosphonate(9j) show the best herbicidal activity against five tested weeds with more than 85% inhibitory rate in pre-emergence.

In planta Mechanism of Action of Leptospermone: Impact of Its Physico-Chemical Properties on Uptake, Translocation, and Metabolism

Leptospermone is a natural β-triketone that specifically inhibits the enzyme p-hydrophyphenylpyruvate dioxygenase, the same molecular target site as that of the commercial herbicide mesotrione. The β-triketone-rich essential oil of Leptospermum scoparium has both preemergence and postemergence herbicidal activity, resulting in bleaching of treated plants and dramatic growth reduction. Radiolabeled leptospermone was synthesized to investigate the in planta mechanism of action of this natural herbicide. Approximately 50% of the absorbed leptospermone was translocated to the foliage suggesting rapid acropetal movement of the molecule. On the other hand, very little leptospermone was translocated away from the point of application on the foliage, indicating poor phloem mobility. These observations are consistent with the physico-chemical properties of leptospermone, such as its experimentally measured logP and pK a values, and molecular mass, number of hydrogen donors and acceptors, and number of rotatable bonds. Consequently, leptospermone is taken up readily by roots and translocated to reach its molecular target site. This provides additional evidence that the anecdotal observation of allelopathic suppression of plant growth under β-triketone-producing species may be due to the release of these phytotoxins in soils.

Synthesis and herbicidal activity of sulfonanilides having a pyrimidinyl-containing group at the 2'-position

A novel series of sulfonanilides having a pyrimidinyl-containing group at the 2′-position was prepared and their herbicidal activities against paddy weeds and selectivity against rice plants were assessed. The structure-activity relationships were probed by substitution of the sulfonyl group, bridge and benzene ring. Among the sulfonamides, difluoromethyl compound showed comparatively high activity and a broad spectrum to control weeds, including Echinochloa oryzicola. The most preferable substitution position on the benzene ring was in the 6-position and the lower alkyl group showed high herbicidal activity and a broad weed control spectrum, and among the compounds tested, the methoxymethyl group was the best. In respect of the bridge moiety, the hydroxyl group was the best. Among the compounds examined, 2′-[(4,6-dimethoxypyrimidin-2-yl)(hydroxy)methyl]-1,1-difluoro-6′-(methoxymethyl)methanesulfonanilide, applied at rates between 4 to 16 g a.i./ha, showed excellent pre-emergence herbicidal activity with a broad spectrum against grass, sedge and broadleaf weeds without injury to rice plants.

Herbicidal Activity of Cineole Derivatives

Essential oils and their constituents have potential as ecologically acceptable pesticides that may also have novel modes of action. In this work hydroxy and ester derivatives of the naturally occurring monoterpenoids 1,8-cineole 3, the main component in most eucalyptus oils, and 1,4-cineole 4 were prepared and their pre-emergence herbicidal activity against annual ryegrass (Lolium rigidum) and radish (Raphanus sativus var. Long Scarlet) investigated in laboratory-based bioassays. 1,8-Cineole, eucalyptus oil and all derivatives showed a dose-dependent herbicidal activity against annual ryegrass and radish with many of the derivatives showing improved herbicidal activity relative to 1,8-cineole and high-cineole eucalyptus oil. Increased activity of cineole ester derivatives compared to their associated hydroxy-cineole and carboxylic acid was not observed. No relationship between lipophilicity of the carboxylic acid portion of cineole ester derivatives and herbicidal activity was observed. The results indicate that these cineole derivatives could be environmentally acceptable herbicides.

Synthesis and herbicidal activity of 2-acylimino-3-phenyl-1,3-thiazolines—A new family of bleaching herbicides—

A novel series of substituted 2-acylimino-1,3-thiazolines was synthesized and their herbicidal activity against upland weeds and selectivity against crops was assessed. The structure–activity relationships were probed by substitution of the thiazoline nucleus and/or an imino group. Highest activity was seen with compounds which contain two substituents: a methyl group at the 5-position of the thiazoline nucleus and a trifluoroacetyl or a difluoroacetyl group on an imino moiety. Among the compounds examined, 2-(N-difluoroacetylimino)-5-methyl-3-(3-trifluoromethylphenyl)-1,3-thiazoline applied at rates between 62.5 and 125 g a.i./ha, showed excellent broad-spectrum pre-emergence herbicidal activity against grass and broadleaf weeds without injury to cotton.

Synthesis and Herbicidal Activity of 1<i>H</i>-2, 3-Benzoxazine Derivatives

A series of 1H-2,3-benzoxazine derivatives were synthesized and their herbicidal activity against upland weeds and selectivity against crops were assessed. Studies of the structure-activity relationship revealed that the strongest herbicidal activity was achieved when position-4 in the benzoxazine ring was substituted with a 3-chloro-4-fluorophenyl or a 3-bromo-4-fluorophenyl group. The treated weeds showed a strong bleaching symptom. Among the compounds examined, 4-(3-chloro-4-fluorophenyl)-1H-2,3-benzoxazine (23) and 4-(3-bromo-4-fluorophenyl)-6-fluoro-1H-2,3-benzoxazine (34), applied at 1.0 kg a.i./ha, showed strong pre-emergence herbicidal activity against upland weeds such as Echinochloa crus-galli and Digitaria ciliaris without affecting soybean.

Discovery of a herbicidal lead using polymer-bound activated esters in generating a combinatorial library of amides and esters.

A combinatorial library containing mixtures of amides and esters was prepared through solid-phase chemistry. The advantages of using solid-phase chemistry over solution-phase chemistry to prepare this library are discussed. The library was screened through a high-throughput whole organism herbicidal assay upon which a mixture containing amides was found to have herbicidal activity. Deconvolution of the mixture provided N-(3-benzoylphenyl)-3-(1,1-dimethylethyl)-1-methyl)-1 H-pyrazole-5-carboxamide as a herbicidal lead with broadleaf and narrowleaf pre-emergence herbicidal activity as low as 100 g/ha on some weed species. This study represents the first report of an agrochemical discovered using a combinatorial approach.

Synthesis and Herbicidal Activity of Substituted Tetrahydronaphthalenes (Part II)

This paper reports the synthesis and the biological activity of substituted 6-alkyl-1,2,3,4-tetrahydro-1,1-dimethylnaphthalenes in which the substituents at the 5- and/or 7-position are varied with a multitide of functional groups. These compounds exhibited pre-emergent herbicidal activity which was a function of the electron-withdrawing ability and the size of the groups substituted at the 5- and/or 7-position. Nitro and/or nitrile groups at these positions tended to optimize activity.

Synthesis and Herbicidal Activity of 3-Aryl-5-(haloalkyl)-4-isoxazolecarboxamides and Their Derivatives

A series of unique 3-aryl-5-(haloalkyl)-4-isoxazolecarboxamides have been prepared which exhibit, in both greenhouse and field studies, significant preemergent and postemergent herbicidal activity in the grams per hectare range against broadleaf and narrowleaf weeds. The key step in the formation of the fully substituted isoxazole ring 2 is 1,3-dipolar cycloaddition of a haloalkylsubstituted acetylenic ester and a nitile oxide intermediate. The 3-aryl-5-(haloalkyl)-4-isoxazole-carboxylate esters 2 are converted to isoxazole-4-carboxamide herbicides 5 and 6, secondary amides 7, and amino acid derivatives 8. Greatest activity was observed with compounds having a combination of three substituents: a substituted phenyl ring in the 3-position, a primary or secondary carboxamide in the 4-position, and a difluorochloromethyl group in the 5-position of the isoxazole ring

Fenarimol Tolerance of Roughstalk Bluegrass Overseeded in Bermudagrass Greens

AbstractBermudagrass (Cynodon spp.) putting greens are overseeded with cool‐season grasses in the fall to maintain a high‐quality putting turf throughout the southern USA. Perennial ryegrass (Lolium perenne L.) has been the predominant grass used for overseeding until recently, when roughstalk (Poa trivialis L.) has been increasingly used for overseeding. Annual bluegrass (Poa annua L.) is a problem winter annual weed that infests most overseeded bermudagrass greens and the weed must be controlled with a herbicide to maintain a high‐quality putting surface. Fenarimol [ɑ(2‐chlorophenyl)‐ɑ‐(4‐chlorophenyl)‐5‐pyrimidinemethanol] has preemergence herbicidal activity on annual bluegrass, but it may also reduce the germination and establishment of roughstalk bluegrass seedlings. A field experiment was conducted over a 2‐yr period to determine the time interval of fenarimol treatments necessary to avoid injury to roughstalk bluegrass overseeded on a bermudagrass green. Overseeded roughstalk bluegrass tolerated fenarimol when applied as (i) a single application at 2.7 kg ha−1, (ii) two applications of 2.0 kg ha−1 each, and (iii) three applications of 1.4 kg ha−1 each, provided the final application was made ≥ 2 wk before overseeding. Quality and density of roughstalk bluegrass were not influenced by fenarimol, provided the last application was made ≥ 2 wk before overseeding in 1991 and ≥ 1 wk before overseeding in 1992. When the final fenarimol application was made during this period, the transition of overseeded roughstalk bluegrass back to bermudagrass was not affected the following spring and early summer.

Pre-emergence herbicidal activity of NSK-850 and its effects on the growth of turfgrasses

Pre-emergence herbicidal activity of NSK-850 and its effects on the growth of turfgrasses

Perspectives on Discovery of Microbial Phytotoxins with Herbicidal Activity

Biologically active natural products of microbial origin are attractive candidates for possible use in agriculture. They may be obtained by fermentation, used in their natural state, or subjected to synthetic modification for specific uses. These natural products are characterized by high specific activity and high selectivity, and they are biodegradable. The structures are extremely diverse and represent many classes of compounds ranging from very complex to simple. Cyclocarbamide A and B, fromStreptoverticilliumsp., have marked preemergence herbicidal activity. Nigerazine A and B, fromAspergillus nigervan Tieghem, also inhibit root growth in certain plants. Citreoviridin, fromPenicillium charlesiiSmith, preferentially controls the growth of monocotyledonous plants, as does a synthetic derivative of cladosporin, fromAspergillus repensDeBary, which bleaches chloroplasts. The 12-membered fungal macrolides (macrocyclic lactones) also inhibit root growth in many test plants and offer templates for further synthetic work. Herbicidins, fromStreptomyces saganonensis, are particularly effective against barnyardgrass, goosegrass, tufted mannagrass, and green panicum.Alternaria eichorniaeNag Raj et Ponnappa produces a toxin that is active against waterhyacinth and represents one of the more exotic structures. The macrocyclic trichothecenes are a significant class of natural products that tend to concentrate against a gradient in seeds of certain plants, which resist these microbially derived metabolites thereby producing seed with “built-in” natural herbicides.

Synthesis and Herbicidal Activity of 2-Difluoromethylthio-1,3,5-triazines

Forty-one 2-difluoromethylthio-1,3,5-triazines were synthesized and their herbicidal activities were evaluated under pot conditions. Some of them showed high potential as useful herbicides against weeds with little phytotoxicity toward crops. 2-Difluoromethylthio-4,6-bis(iso- propylamino)-1,3,5-triazine (exp. code No. SSH-108) showed a particularly high specific pre-emergence herbicidal activity. Their activities and selectivities were compared with those of prometryn.