Herbicidal activity of slow-release herbicide formulations in wheat stands infested by weeds

Assessment of the efficacy of slow-release formulations of the tribenuron-methyl herbicide in field-grown spring wheat

The efficacy of slow-release formulations of tribenuron-methyl (TBM) embedded in the matrix of degradable poly(3-hydroxybutyrate) blended with birch wood flour [polymer/wood flour/herbicide 50/30/20 wt.%] was compared with the efficacy of TBM as the active ingredient of the Mortira commercial formulation, which was applied as post-emergence spray to treat spring wheat cv. Novosibirskaya 15. The study was conducted in Central Siberia (in the environs of the city of Krasnoyarsk, Russia) from May to August 2020. The biological efficacy of the embedded TBM was 92.3%, which was considerably higher than the biological efficacy of the Mortira formulation used as the post-emergence spray (15.4%). The embedding of TBM into degradable blended matrix enabled long-duration functioning of this unstable herbicide in soil. The sensitivity of weed plants to TBM differed depending on the species. TBM was more effective against A. retroflexus and A. blitoides, which were killed at an earlier stage, than against C. album and G. aparine, whose percentage increased in the earlier stage and which were controlled by the herbicide less effectively and at later stages. On the plot treated with the embedded herbicide, the parameters of the wheat yield structure were the best, and the total yield was the highest: 3360 ± 40 kg/ha versus 3250 ± 50 kg/ha in the group of plants sprayed with the Mortira formulation. The grain produced in all groups was of high quality and was classified as Grade 1 food grain. The highest quality parameters (grain hectoliter mass, gluten, and protein contents) were obtained in the group of plants treated with the embedded herbicide. The study of the embedded TBM confirmed the high efficacy of the experimental formulation.

Effects of Metribuzin Herbicide on Some Morpho-Physiological Characteristics of Two Echinacea Species

Echinacea is a perennial plant that is used for its phytotherapeutic potential. Echinacea crops are often affected by invasive weeds. One of the most effective strategies in weed control is the use of chemicals such as herbicides. However, herbicides also affect the physiological and morphological processes of Echinacea. For this reason, the aim of this study was to determine the effects of different dosages (0, 250, 500, 750, 1000, and 1250 g ha−1) of the postemergent herbicide metribuzin on some morphological and physiological characteristics of Echinacea purpurea and Echinacea angustifolia collected from different locations in Iran (E. purpurea from the Shiraz and Isfahan regions and E. angustifolia from the Ardestan and Kazerun regions). Application of metribuzin decreased leaf dry weight for both Echinacea species at high doses (750 and 1250 g ha−1). At high metribuzin dose (1250 g ha−1), E. purpurea Shiraz leaves showed an increase in MDA (malondialdehyde) up to 9.14, while in other species the MDA content was lower. Minimum and maximum fluorescence increased at both the registered dosage (500 g ha−1) and at high doses (750–1250 g ha−1) of metribuzin treatments in both species. The Fv/Fm (maximum quantum yield) value was reduced in herbicide treated species, compared to the control, starting at the 250 g ha−1 dose, and was lowest at 750 g ha−1 dose. The results of this study indicate that metribuzin has adverse effects on the physiology and morphology of Echinacea species at dosages above 500 g ha−1.

Efficacy of embedded metribuzin and tribenuron-methyl herbicides in field-grown vegetable crops infested by weeds

The purpose of the present study was to investigate the efficacy of the experimental formulations of the metribuzin (MET) and tribenuron-methyl (TBM) herbicides embedded in the matrix of degradable poly-3-hydroxybutyrate blended with wood flour in field-grown tomato and beet crops infested by weeds. There is a necessity to develop environmentally friendly and effective means to protect plants because of the shortcomings of the free herbicide forms such as the environmentally unsafe spray application of solutions and suspensions of the widespread metribuzin and tribenuron-methyl herbicides, removal from soil during watering events and rains, and transport to natural aquatic environments, where the herbicides accumulate in the trophic chains of biota. Free TBM is also rapidly inactivated in soil and metabolized to nontoxic products in plants. The efficacy of experimental formulations of metribuzin and tribenuron-methyl embedded in the matrix of degradable poly-3-hydroxybutyrate blended with wood flour was tested in field-grown tomato and beet crops infested with weeds. Application of metribuzin resulted in the highest productivity of tomatoes (2.3 kg/m²) and table beet (3.4 kg/m²), improved biometric parameters of tomato fruits and beet roots, and caused reduction in nitrate nitrogen concentrations in them. The mode of herbicide delivery did not affect sugar contents, but application of both metribuzin and tribenuron-methyl induced a 1.7-fold and 1.4-fold, respectively, increase in vitamin C concentrations in tomato fruits and beet roots relative to the vegetables grown on the subplots treated with free herbicides and the intact plants. Embedded herbicides can be used as preemergence herbicides in the field. Fig. a Graphical abstract.

Efficacy of Slow-Release Formulations of Metribuzin and Tribenuron Methyl Herbicides for Controlling Weeds of Various Species in Wheat and Barley Stands

The herbicidal activity of long-acting formulations of metribuzin and tribenuron methyl herbicides embedded in granules prepared from a mixture of degradable poly(3-hydroxybutyrate) and birch wood flour was studied in laboratory-grown weeds of various species and in wheat Triticum aestivum and barley Hordeum vulgare stands infested by weeds. The constructed formulations effectively suppressed all species of weeds studied. The biological effectiveness of herbicide formulations toward intact plants in wheat and barley stands infested with weeds was close to 100%, which was significantly higher than the effect of their free forms. The more effective suppression of weeds by embedded herbicides was beneficial for the growth of crops whose aboveground biomass was 8-13 to 20% greater than that of the crops in the treatments with free herbicides. Embedded metribuzin and tribenuron methyl exhibit sustained and pronounced herbicidal activity and are effective for pre-emergence soil application for crops infested with weeds of various species.

Designing for effective controlled release in agricultural products: new insights into the complex nature of the polymer-active agent relationship and implications for use

BACKGROUND

Various active chemical agents, such as soil microbial inhibitors, are commonly applied to agricultural landscapes to optimize plant yields or minimize unwanted chemical transformations. Dicyandiamide (DCD) is a common nitrification inhibitor. However, it rapidly decomposes under warm and wet conditions, losing effectiveness in the process. Blending DCD with an encapsulating polymer matrix could help overcome this challenge and slow its release. Here, we encapsulated DCD in a biodegradable matrix of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and investigated the effects of DCD crystal size and loading rates on release rates.

RESULTS

Three DCD crystal size fractions (0-106, 106-250 and 250-420 μm) were blended with PHBV at 200, 400, 600 and 800 gkg^-1 loadings through extrusion processing and release kinetics were studied in water over 8 weeks. For loadings ≥ 600 g kg^-1 , more than 95% release was reached within the first 7 days. By contrast, at 200 g kg^-1 loading only 10%, 36% and 57% of the DCD was mobilized after 8 weeks in water for 0 to 106 μm, 106 to 250 μm and 250 to 420 μm crystal size fractions, respectively.

CONCLUSION

The lower percolation threshold for this combination of materials lies between 200 and 400 g kg^-1 DCD loading. The grind size fraction of DCD significantly affects the quantity of burst release from the surface of the pellet, particularly below the lower percolation threshold. The results presented here are likely translatable to the encapsulation and release of other crystalline materials from hydrophobic polymer matrices used in controlled release formulations, such as fertilizers, herbicides and pesticides. © 2020 Society of Chemical Industry.

Biological effects of the free and embedded metribuzin and tribenuron-methyl herbicides on various cultivated weed species

The present study addresses the herbicidal activity and biological effects of the metribuzin (MET) and tribenuron-methyl (TBM) herbicides used to control various weed species (Amaranthus retroflexus, Sinapis arvensis, and Leucanthemum maximum). The effects of the free herbicides and the herbicides embedded in granules of degradable polymer poly-3-hydroxybutyrate [P(3HB)] blended with birch wood flour were compared. Metribuzin, regardless of the form, caused 100% mortality of the three weeds by day 21. The herbicidal activity of tribenuron-methyl was lower than that of metribuzin, but the embedded TBM was superior to the free herbicide in the length and strength of its action on the weeds. Both metribuzin forms dramatically decreased the main parameters of fluorescence: maximum quantum yield of photosystem-II [Y(II)_max], maximum quantum yield of non-photochemical quenching [Y(NPQ)_max], and maximum rate of non-cyclic electron transport [ETR_max] and concentrations of chlorophyll a and b. The effect of the embedded TBM on the photosynthetic activity of the weeds was lower in the first two weeks of the growth of herbicide-treated plants but lasted longer than the effect of the free TBM and increased over time. Embedding of metribuzin in the matrix of degradable blend did not decrease its herbicidal activity.

Constructing sustained-release herbicide formulations based on poly-3-hydroxybutyrate and natural materials as a degradable matrix

BACKGROUND

The purpose of the present study was to develop ecofriendly herbicide formulations. Its main aim was to develop and investigate slow-release formulations of herbicides (metribuzin, tribenuron-methyl, and fenoxaprop-P-ethyl) of different structure, solubility, and specificity, which were loaded into a degradable matrix of poly-3-hydroxybutyrate (P(3HB)) blended with available natural materials (peat, clay, and wood flour).

RESULTS

Differences in the structure and physicochemical properties of the formulations were studied depending on the type of the matrix. Herbicide release and accumulation in soil were associated with the solubility of the herbicide. Fourier-transform infrared spectroscopy showed that no chemical bonds were formed between the components in the experimental formulations. Degradation of the formulations in agro-transformed soil in laboratory conditions was chiefly influenced by the shape of the specimens (granules or pellets) while the effect of the type of filler (peat, clay, or wood flour) was insignificant. The use of granules enabled more rapid accumulation of the herbicides in soil: their peak concentrations were reached after 3 weeks of incubation while the concentrations of the herbicides released from the pellets were the highest after 5-7 weeks. Loading of the herbicides into the polymer matrix composed of the slowly degraded P(3HB) and natural materials enabled both sustained function of the formulations in soil (lasting between 1.5 and ≥3 months) and stable activity of the otherwise rapidly inactivated herbicides such as tribenuron-methyl and fenoxaprop-P-ethyl.

CONCLUSION

The experimental herbicide formulations enabled slow release of the active ingredients to soil. © 2019 Society of Chemical Industry.

Biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) microcapsules for controlled release of trifluralin with improved photostability and herbicidal activity

Microencapsulation of pesticide is a promising technology to reduce the negative environmental impact and benefit the sustainable development. Trifluralin, commonly used as a selective pre-emergence herbicide, is vulnerably subject to loss by volatilization and decomposition by sunlight when applied to the surface of soils. In the present study, trifluralin has been encapsulated using biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHB) polymers as carriers to develop controlled release formulations. PHB trifluralin microcapsules were obtained using a convenient solvent evaporation method. The influences of preparation parameters on the size and its distribution of the microcapsules were discussed. The particle size decreased from 4.44 μm to 2.50 μm as the shearing speeds increased from 4000 r/min to 12,000 r/min, and the value decreased from 3.64 μm to 3.23 μm as the mass fraction of emulsifier polyvinyl alcohol increased from 0.5% to 2.0%. The loading content (LC) as well as the encapsulation efficiency (EE) of trifluralin microcapsules are multiple factors dependent. Orthogonal table L9(3⁴) was designed and range analysis was used to suggest the optimal preparation parameters. When performed under the optimized conditions, the corresponding LC and EE were 16.50% and 90.65%, respectively. The release of trifluralin from PHB microcapsules showed slow and sustained patterns, which could be easily achieved by modifying the preparation parameters including shearing speed and concentration of emulsifier. Compared to conventional trifluralin formulation of emulsifiable concentrate, trifluralin microcapsules exhibited significantly improved photostability and herbicidal activity against target weed barnyardgrass. These results demonstrated that microencapsulation with PHB could dramaticlly improve the effective utilization rate and decrease the dosage of such agricultural chemicals.

Understanding the Mobilization of a Nitrification Inhibitor from Novel Slow Release Pellets, Fabricated through Extrusion Processing with PHBV Biopolymer

Dicyandiamide (DCD) has been studied as a stabilizer for nitrogen fertilizers for over 50 years. Its efficacy is limited at elevated temperatures, but this could be addressed by encapsulation to delay exposure. Here, poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) was investigated as a biodegradable matrix for the encapsulation of DCD. Cylindrical ∼3 mm × 3 mm pellets were fabricated through extrusion processing with 23 wt % DCD. Release kinetics were monitored in water, sand, and both active and γ-irradiated agricultural clay loam soils. Raman maps showed a wide particle size distribution of DCD crystals and indicated that Hitachi's classic moving front theory did not hold for this formulation. The inhibitor release kinetics were mediated by four distinct mechanisms: (i) initial rapid dissolution of surface DCD, (ii) channeling of water through voids and pores in the PHBV matrix, (iii) gradual diffusion of water and DCD through layers of PHBV, and (iv) biodegradation of the PHBV matrix. After ∼6 months, 45-100% release occurred, depending on the release media. PHBV is shown to be an effective, biodegradable matrix for the long-term slow release of nitrification inhibitors.

Antifungal activity of P3HB microparticles containing tebuconazole

In this study, tebuconazole (TEB)-loaded poly-3-hydroxybutyrate (P3HB)-based microparticles were developed and comprehensively characterized. TEB-loaded microparticles with the initial loading amounts of the fungicide of 10, 25, and 50% of the polymer mass (TEB 10, TEB 25, and TEB 50%) were prepared using emulsion technique. Encapsulation efficiency of TEB varied from 59 to 86%. As the loading amount was increased, the average diameter of microparticles increased too, from 41.3 to 71.7 µm, while zeta potential was not influenced by TEB loading, varying between -32.6 and -35.7 mV. TEB was gradually released from the microparticles to the model medium, and after 60 d, from 25 to 43% of TEB was released depending on the content of the encapsulated fungicide. The data obtained from in vitro TEB release were fitted to different mathematical models. It was shown that the release profiles of TEB could be best explained by the Zero-order, Higuchi, and Hixson-Crowell models. The antifungal activity of the P3HB/TEB microparticles against phytopathogenic fungi Fusarium moniliforme and Fusarium solani was demonstrated by in vitro tests conducted in Petri dishes. Thus, hydrophobic agrochemicals (TEB) can be effectively encapsulated into P3HB microparticles to construct slow-release formulations.