Herbicide performance in the control of Conyza spp. where three plant heights

Intensive use of the herbicide glyphosate has led to herbicide resistant Conyza spp. populations. Thus, there is a need to indicate alternative herbicides and the appropriate developmental stage for controlling these populations. This study identifies alternatives for controlling glyphosate-resistant horseweed, with treatment applications at different plant heights. For this purpose, field experiments were conducted in the 2016/17 and 2017/18 crop years. The evaluated treatments were: glyphosate (540 g ae ha-1), glyphosate (1080 g ae ha-1), glyphosate (2160 g ae ha-1), glyphosate (3240 g ae ha-1), glyphosate + 2.4-D (1080 + 1005 g ae ha-1), glyphosate + saflufenacil (1080 + 49 g ae/ai ha-1), paraquat (400 g ai ha-1), diquat (400 g ai ha-1), ammonium glufosinate (600 g ai ha-1), and control (without application). These treatments were applied to plants with a maximum of 5 cm; plants between 6 and 15 cm; and plants between 16 and 25 cm. The results showed that glyphosate did not control weeds, regardless of rate. With the exception of 2,4-D, which needs complementation with sequential application of another contact herbicide, all alternatives were viable for the control of Conyza spp. plants with a maximum height of 5 cm.

CHEMICAL CONTROL OF ADULT SOURGRASS IN COFFEE CROPS, THROUGH VARIOUS ASSOCIATIONS

Weed management in coffee plants is carried out largely through the adoption of chemical control, with the use of herbicides. In this context, one of the species that most affects the development of coffee plants, and due to its difficulty in control, is sourgrass. Above all, most sourgrass biotypes are not efficiently controlled with the herbicide glyphosate, which is the most used in coffee growing. Thus, the search for strategies that can minimize the damage caused by this weed, appears with increasing demand, due to the great damage to coffee plants. Therefore, the objective of this study was to evaluate the chemical control of adult sourgrass in coffee plants, through several associations. Treatment control efficiency was visually evaluated, where a scale ranging from 0 to 100 was used, with 0 corresponding to the absence of symptoms and 100 corresponding to the total control of weed plants by the action of herbicides, respectively. This evaluation method was used at 7, 14, 21, 28, 35 and 42 days after application. The data obtained were subjected to analysis of variance using the SISVAR statistical software. The association of the herbicides Fluazifop-p-butyl and Clethodim, implies greater efficiency in controlling sourgrass over time. The association of the herbicide ammonium glufosinate with systemic herbicides implies a reduction in the control capacity of sourgrass plants over time.

MANAGEMENT OF GLYPHOSATE-RESISTANT HAIRY FLEABANE AND CONTRIBUTION OF THE PHYSIOLOGICAL POTENTIAL OF SEEDS TO RESISTANCE

ABSTRACT Hairy fleabane (Conyza bonariensis L.) is a major weed of the conventional crop systems. Therefore, the objectives of the present study were to assess the responses of glyphosate-susceptible (S) and -resistant (R) C. bonariensis at various developmental stages and evaluate the physiological potential of seeds to propose alternative herbicides for the control of this weed. Two experiments were performed in replicates. The first experiment was performed in a greenhouse, arranged in a 2 x 3 x 10 factorial design. Specifically, two hairy fleabane biotypes (S and R) at different developmental stages (I, II, and III) were subjected to various treatments (glyphosate, chlorimuron-ethyl, metsulfuron-methyl, diclosulam, ammonium glufosinate, paraquat, paraquat+diuron, diquat, 2,4-D, and control). Percentage control was evaluated at 7, 14, 21, and 28 days after the application of the treatments (DAT), and shoot dry mass (SDM) was measured at 28 DAT. The second experiment was performed in a laboratory to evaluate the physiological potential of seeds based on the weight of 1000 seeds (TSW); shoot length (SL), radicle length (RL), total length (TL), fresh seedling mass (FSM), dry seedling mass (DSM), accelerated aging (AA) and cold test (CT), and germination (G) in response to cold and accelerated aging. The alternative herbicides tested effectively controlled biotype R up to the stage -I. Seeds of biotype R showed higher physiological potential in terms of all analyzed variables and exhibited greater tolerance to adverse conditions during seedling establishment. Therefore, strategies for the management of glyphosate-resistant hairy fleabane should aim at preventing new seed production.

Reduction of Ryegrass (Lolium multiflorum Lam.) Natural Re-Sowing with Herbicides and Plant Growth Regulators

Ryegrass (Lolium multiflorum Lam.) is the main winter weed of crops in Southern Brazil. High competitiveness, adaptability, widespread resistance to herbicides and seed dormancy make the plant a permanent problem. Herbicides, as well as plant growth regulators, can be used as a management option for ryegrass seed production, however there is no consensus among authors at which stage of the plant the application is most effective. Thus, this study aimed to evaluate the production and physiological quality of ryegrass seeds in response to the application of herbicides and plant growth regulators in three stages of plant development (inflorescence emergence, flowering and fruit development). Each treatment consisted of applying two different doses of each of the active ingredients: ammonium glufosinate, clethodim, glyphosate, iodosulfuron-methyl, paraquat and 2,4-D (herbicides); ethephon and trinexapac-ethyl (plant growth regulators), still an untreated control, totaling 17 treatments for each stage of development. The experimental design used was randomized blocks, with three replications. The variables evaluated were: seed production (kg ha−1), thousand seed weight (g), viability (%), germination (%), first germination count (%), dormant seeds (%) and dead seeds (%). The ryegrass seed production reduced 100% with clethodim, glyphosate, ammonium glufosinate or paraquat applied in the inflorescence emergence or flowering stages. In the fruit development stage, all treatments (herbicides and plant growth regulators) caused deleterious effects on seed production, the greatest effect occurred with paraquat (95%). Paraquat, ammonium glufosinate and clethodim affected the physiological quality of the seeds when applied in fruit development stage. This research demonstrated that the application of herbicides in the ryegrass reproductive stage decreases its seedbank replenishment (natural re-sowing), with the potential to harm its progeny.

Photosynthetic index and nitrogen assimilation in rapeseed seedlings transplanted in soil with ammonium glufosinate

ABSTRACT: Herbicide application is an effective weed control method for mitigating crop yield loss; however, herbicide overuse can cause toxicity in non-target plants. The present study evaluated the effects of glufosinate at recommended dose for agricultural application (0.45 kg ha-1) and at overuse dose (0.90 kg ha-1) glufosinate application on photosynthetic performance and nitrogen assimilation of the rapeseed varieties D148 and Zhongshuang 11 (ZS11). Both glufosinate concentrations significantly decreased the content of chlorophyll and nitrogenous compounds, except free proline, and the activity of glutamine synthetase and glutamate synthase, and increased the activity of glutamic acid dehydrogenase in both varieties. When the concentration of glyphosate was 0.45kg ha-1, the nitrogen assimilation of the two varieties decreased, which indicated that the recommended dosage inhibited the nitrogen assimilation of the two varieties; however, the increase of net photosynthetic rate of D148 and the decrease of that of ZS11 mean that D148 is more tolerant to the recommended dose of glyphosate than ZS11. The 0.90 kg ha-1 dosage was toxic to both rapeseed varieties. Overall, our results indicated that herbicide overuse inhibited the photosynthetic rate and nitrogen assimilation in rapeseed seedlings, and it is essential to apply a suitable glufosinate dose based on the variety grown to minimize adverse effects on crops and environment.

DOES CHEMICAL DESICCATION AND HARVEST TIME AFFECT THE PHYSIOLOGICAL AND SANITARY QUALITY OF SOYBEAN SEEDS?

ABSTRACT The use of desiccants may result in seeds with high physiological and sanitary quality due to the shorter period of exposure to field adverse conditions before the maturity stage for harvest. This study evaluated the effect of chemical desiccants and harvest times on the physiological and sanitary quality of soybean seeds. The experiment consisted of a randomized block design, arranged in a factorial scheme (4 × 3) + 1, with four replications. The first factor corresponded to four desiccation (grammoxone-2 L ha-1, glufosinate-2 L ha-1, reglone-1.5 L ha-1, and saflufenacil-40 g ha-1) applied at the R7.1 phenological stage (physiological maturity and 65% moisture with three harvest times (0, 7, and 14 days after the R8 phenological stage) and additional treatment (control, application of water only, and harvest at the R8 stage), with four replications. The use of the grammoxone desiccant and seeds harvested at seven days after the R8 stage resulted in soybean seeds of the highest physiological quality, as observed for the variables germination, moisture damage, mechanical damage, and incidences of Colletotrichum sp., Phomopsis sp., Penicillium sp. Fusarium sp., Cercospora kikuchii, and Alternaria sp. Seeds harvested at the R8 + 14 stage had the greatest losses in seed quality. The use of ammonium glufosinate and saflufenacil as desiccants is not recommended due to the reduction in the physiological quality of soybean seeds.

Effect of Phosphinothricin on Transgenic Downy Birch (Betula pubescens Ehrh.) Containing bar or GS1 Genes

Weeds are a big problem in agriculture and forestry, and herbicides are the main tools to control them. Phosphinotricin (ammonium glufosinate, PPT) is one of the most effective non-selective herbicides, to which weeds hardly gain resistance, but the reasons for its effect and toxicity to plants are still unclear, and especially, it is little studied in trees, including transgenic ones. We studied the physiological responses of downy birch (Betula pubescens Ehrh.) containing the herbicide resistance bar gene or the cytosol glutamine synthetase GS1 gene (the target enzyme of the herbicide) to PPT-based Basta herbicide treatment in various doses under open-air conditions during two years. Birch saplings with the bar gene were resistant to a double field dose (10 L/ha), but the expression of the GS1 gene only slightly increased resistance compared to the control. Herbicide treatment increased the ammonium level in leaf tissue by 3–8 times, but this, apparently, was not the main cause of plant death. Among leaf pigments, chlorophyll B was the most resistant to PPT, and carotenoids were the most sensitive. Responses of birch trees with the GS1 gene (accumulation of ammonium, pigment content, and dehydration) during treatment with a low dose of herbicide were less pronounced than in control plants. One-year-old control and transgenic plants with the GS gene died after 2.5 L/ha treatment, and two-year-old plants lost foliage after such treatment but remained alive and developed buds four weeks after treatment. Herbicide treatment of plants with the bar gene did not cause significant deviations in height (first year) or the accumulation of aboveground biomass (second year). The obtained results improve our understanding of the effect of PPT on woody plants and can be used both to clarify mechanisms of herbicide action and in plantation forestry.

Ammonium glufosinate and triazine herbicides have side effects on soil microorganisms and pathogens

Goal. Analysis and synthesis of research results regarding the beneficial and negative side effects of ammonium glufosinate and thiazine herbicides on microorganisms. Methods. System-analytical, abstract-logical, empirical. Results. Information on the side effects of herbicides with the content of the active substance glufosinate ammonium and derivatives of thiazine herbicides is given. One of the side effects of herbicides that attracts attention is their biological activity. The biological activity of herbicides goes beyond the effects on target organisms and, thus, herbicides can influence the plant-pathogen interaction through their effect on the causative agent or on the surrounding soil microorganisms, including symbiotic relationships. As a side effect, both a decrease and an increase in diseases caused by phytopathogens that affect leaves, stems or roots are established. However, in some cases, the results obtained in in vitro experiments differed from the results obtained in field conditions in vivo or on a host plant. The phenomenon of the manifestation of side effects of herbicides was first discovered in the early 1940s and began to be studied in more detail since 1960. Conclusions. Generalized information about the history, studies of the side effects of herbicides on different cultures and in different conditions in the world. It is important that such effects are not fully studied, and these mechanisms attract the attention of scientists for their further research. Future studies are planned to be carried out using high-precision methods, such as chip-based technologies, to study all the mechanisms involved in the pathogen-plant interaction, which are modulated by herbicides. This trilateral relationship today is studied as a molecular and biochemical cross-linkage between a plant and a pathogen, a plant and a herbicide, as well as a pathogen and a herbicide. Active studies by foreign scientists of the side effects of herbicides show that in Ukraine, as an agrarian state, it is necessary to purposefully investigate the effect of herbicides on soil microorganisms and pathogens to optimize the use of plant protection products in agricultural production.

Rapid necrosis: a novel plant resistance mechanism to 2,4-D

Plants of Sumatran fleabane [Conyza sumatrensis (Retz.) E. Walker] were identified in a field with an unusual rapid leaf-injury herbicide symptoms after application of 2,4-D in mixture with glyphosate. The objectives of this study were to confirm the occurrence of resistance to 2,4-D herbicide and to characterize the occurrence of rapid necrosis as the mechanism associated with the herbicide resistance in C. sumatrensis. The studies performed were an initial screening, effect of 2,4-D alone and associated with glyphosate, cross- and multiple-resistance evaluation, effect of commercial formulation and analytical product, and rate of H2O2 evolution. The Marpr9-rn accession was identified with rapid necrosis symptoms and survival to 804 g ae ha−1 of 2,4-D. The resistance factor to the herbicide 2,4-D was 18.6 at 49 d after spraying. The analytical product 2,4-D and the commercial formulation resulted in similar symptoms of rapid necrosis. This symptom did not occur for the six other auxinic herbicides (dicamba, florpyrauxifen-benzyl, fluroxypyr, halauxifen-methyl, picloram, and triclopyr), indicating absence of cross-resistance. Multiple resistance to the herbicides paraquat, saflufenacil, and ammonium glufosinate was not identified in the Marpr9-rn population. However, survival following treatment with the herbicides glyphosate and chlorimuron-ethyl occurred. The evolution of H2O2 began at 15 min after application and was less pronounced in low light. These results indicate the first case of resistance to 2,4-D and occurrence of rapid necrosis in C. sumatrensis.

Efficiency of glyphosate and ammonium glufosinate against common ragweed (Ambrosia artemisiifolia L.) in vineyards

The use of glyphosate (720-2880 g/h a.i.) and ammonium glufosinate herbicides (375-1500 g/h a.i.) to control of common ragweed (Ambrosia artemisiifolia L.) has been studied in trials (2013-2018) in the vineyards of Rkatsiteli, Liang and Cabernet Sauvignon in Abinsk district of Krasnodar region. Accounting of weeds was done by a quantitative method with counting the number of each weed species in each plot. Counts were performed before the treatment and in 15, 30 and 45 days after spraying. The effi cacy of herbicide was determined in relation to the untreated control and expressed as a percentage. The main evaluation criterion was the eff ectiveness of 100 % in one of the accounts or the average (for all counts) effi ciency of more than 90 %. The results showed that in 95 % of trials spraying of 1440 g/h of glyphosate 1440 g/h of glyphosate (a.i.) and higher ensured processing effi ciency exceeding 90 %. Herbicides such as Roundup, containing 360 g/l of isopropylamine salt, can be recommended for use to control of common ragweed in the application rate 4.0 l/ha. Destruction of all common ragweed observed when using not less than 600 g/h glufosinate ammonium. Thus, Herbicides such as Basta, containing 150 g/l of ammonium glufosinate, to control of common ragweed should be applied by fractional application vegetative weeds (2.5 l/h + 1.5 l/h).