Prospects for Bioherbicides

New solutions to weed management are needed now more than ever. Ag retailers, university extension specialists and farmers consider the evolution of herbicide-resistant weeds "one of the most significant developments in agriculture today." Indeed, weed resistance is not just a US problem, but a global one. There are currently 505 unique cases of herbicide resistant weeds globally, with 264 species. Weeds have evolved resistance to 21 of the 31 known herbicide sites of action and to 164 different herbicides. Herbicide resistant weeds have been reported in 95 crops in 71 countries. According to Duke, no new herbicide modes of action have been introduced since the 1980s. Since this paper, only one herbicide with a new mode of action (cyclopyrimorate) has been commercialized. Some major agrichemical companies have announced new discoveries and new modes of action coming in the future, but these are some years off. Given this state of weed management, one would think that biological or natural product herbicides with new modes of action would already be making headway in the market. Unfortunately, few new biological products have been commercialized. The technical difficulty in finding bioherbicides that can compete with the spectrum and price of chemical herbicides has left agriculture with a paucity of new herbicides based on natural products. Most products are targeted at organic agriculture because of their higher manufacturing cost. These products are typically short residual, burndown products that require high volumes and multiple applications. Examples are clove and orange oils. Other natural active ingredients include acetic acid (vinegar), FeHEDTA, NaCl, pelargonic acid, and caprylic and capric acids. This paper reviews the reasons for the lack of new bioherbicides, current and pipeline products and how new technologies may accelerate their progress.

Seed dressing with mefenpyr-diethyl as a safener for mesosulfuron-methyl application in wheat: The evaluation and mechanisms

Mesosulfuron-methyl is always applied by foliar spraying in combination with the safener mefenpyr-diethyl to avoid phytotoxicity on wheat (Triticum aestivum L.) cultivars. However, it was observed that the tolerance of Tausch’s goatgrass (Aegilops tauschii Coss.) to mesosulfuron-methyl significantly increased in the presence of mefenpyr-diethyl by performing bioassay. This confirmed phenomenon may lead to overuse of mesosulfuron-methyl and weed resistance evolution in field conditions. Therefore, we tested the effect of wheat seed dressing with mefenpyr-diethyl as a possible alternative and disclosed the underlying mechanisms by herbicide dissipation study, enzymatic analysis and transcriptome profiling. The results suggest that increase of ALS activity, enhancement of metabolic processes, and other stress responses are crucial for the regulation of herbicide detoxification induced by mefenpyr-diethyl. Additionally, transcription factors such as AP2/ERF-ERF, bHLH, NAC, and MYB, and protein kinase such as RLK-Pelle_DLSV might play vital regulatory roles. The current study has important implications for mesosulfuron-methyl application in wheat field to control Tausch’s goatgrass and provides a comprehensive understanding of the protective effect of mefenpyr-diethyl.

Comprehensive machine learning based study of the chemical space of herbicides

Widespread use of herbicides results in the global increase in weed resistance. The rotational use of herbicides according to their modes of action (MoAs) and discovery of novel phytotoxic molecules are the two strategies used against the weed resistance. Herein, Random Forest modeling was used to build predictive models and establish comprehensive characterization of structure–activity relationships underlying herbicide classifications according to their MoAs and weed selectivity. By combining the predictive models with herbicide-likeness rules defined by selected molecular features (numbers of H-bond acceptors and donors, logP, topological and relative polar surface area, and net charge), the virtual stepwise screening platform is proposed for characterization of small weight molecules for their phytotoxic properties. The screening cascade was applied on the data set of phytotoxic natural products. The obtained results may be valuable for refinement of herbicide rotational program as well as for discovery of novel herbicides primarily among natural products as a source for molecules of novel structures and novel modes of action and translocation profiles as compared with the synthetic compounds.

Sifat Campuran Herbisida Berbahan Aktif Bentazon dan MCPA Terhadap Gulma Daun Lebar, Teki dan Rumput

<p>Weed control using a single herbicide with same active ingredients can add the risk of weed resistance. Using mixed herbicides can increase the spectrum of weeds controlled, and inhibit weed resistance. Herbicide mixture with two or more types of active ingredients will show the interactions between one and another ingredient. These interactions could be synergistic, antagonistic, and additive. The research was to determine the response of mixed herbicide Bentazon, MCPA 460 g. L⁻¹ and their mixed characteristic. This experiment was conducted from June until August 2019 in the greenhouse at the Faculty of Agriculture, Universitas Padjadjaran. The treatment consisted of three types of herbicides with six dose levels, namely a single herbicide of Bentazon 400 g. L⁻¹ and MCPA 60 g. L⁻¹ (4; 2; 1; 0.5; 0.25; 0 L.ha⁻¹), a mixed herbicide Bentazon MCPA 460 g.L⁻¹ (5; 2.5; 1.25; 0.625; 0.3215; 0 L.ha⁻¹) with four replications. The target weeds tested were <em>Spenochlea zeylanica</em>, <em>Ludwigia hyssopifolia</em>, <em>Fimbristylis miliacea</em>, and <em>Cyperus iria</em> was taken from the Ciparay area. Data were analysed by linear regression analysis and multiplicative survival model (MSM) method to determine the LD50 treatment and expectation. The result showed that compound herbicides of Bentazon and MCPA LD50 treatment (0,3857 g.ha⁻¹) had smaller value than LD50 expectation (0,6943 g.ha⁻¹) with a ecotoxicity value of 1.8 (&gt; 1), so that the herbicide mixture was synergistic.</p>

A Non-destructive Leaf Disc Assay for Rapid Diagnosis of Weed Resistance to Multiple Herbicides

Weed resistance survey that monitors the spread of resistant weeds has been mainly conducted through time-consuming, labor-intensive and destructive greenhouse herbicide screens. As an alternative, we here introduce a non-destructive leaf disc assay based on chlorophyll fluorescence (Fv/Fm values which measure photosynthesis efficiency) allowing the detection of resistance to both systemic and contact herbicides within ˜48h. Current study validated the assay on detecting resistance to fomesafen, glyphosate, and dicamba in Palmer amaranth (Amaranthus palmeri S. Watson), waterhemp [Amaranthus tuberculatus (Moq.) Sauer], kochia [Bassia scoparia (L.) A.J. Scott] and goosegrass [Eleusine indica (L.) Gaertn.]. Negative correlation between the Fv/Fm values and the spray injury levels was observed in all herbicide-weed combinations at the discriminating doses, except for glyphosate in Amaranthus. The correlation coefficients were -0.41 for fomesafen (10µM, p<0.0001) in Amaranthus, -0.92 for glyphosate in E. indica (250µM, p<0.0001), and -0.44 for dicamba in B. scoparia (800 µM, p=0.0023), respectively. At the population level, the assay clearly separated susceptible from highly resistant populations. However, the assay showed lower sensitivity in distinguishing populations of different resistance levels or separating low resistance from susceptible populations. At the individual plant level, results from the leaf disc assay and whole plant spray tests were concordant in 85.5%, 92.3%, and 71.7% of the plants tested for fomesafen-Amaranthus, glyphosate-Eleusine and dicamba-Bassia, respectively. The assay yielded 1-15% false positive and 6-13% false negative results across herbicides. The current study demonstrated that the leaf disc assay is a useful tool to identify weed resistance. Optimization is needed to improve its sensitivities and expand its usage to more diverse herbicide-weed species combinations.

Assessment of allelopathic compounds to develop new natural herbicides : A review

Herbicides are a crucial tool for weed control in crops. However, their continuous and indiscriminate uses have caused environmental pollution and development of weed resistance. Hence, there is an urgent need to minimise the dependence on synthetic herbicides. Allelopathy may be used to develop new bioherbicides to inhibit germination and growth of weeds. There is a great potential to develop eco-friendly herbicides from plants, but little research has been done so far in this context. Identification and quantification of natural weed control compounds (allelochemicals) of plants may help to develop natural herbicides (based on indigenous/invasive weed species), to reduce the dependence on synthetic herbicides and improve the integrated weed management programme in crops. This review describes thepotential allelochemicals present in plants, which may be used as a tool to develop new natural herbicides.

Multiple resistance of Conyza sumatrensis to three mechanisms of action of herbicides

Fleabane (Conyza spp.) is an important weed in grain production systems and is currently one of the most problematic weeds in Brazil. An important factor related to weeds such as fleabane is the characteristic of herbicide-resistant biotypes developed under selection pressure, with multiple resistance previously detected for Conyza spp. Thus, the aim of this study was to demonstrate the multiple resistance of Conyza sumatrensis to the herbicides paraquat, glyphosate, and chlorimuron. From the F2 seeds of biotypes with suspected resistance to paraquat, glyphosate, and chlorimuron, dose-response greenhouse experiments were conducted for the three herbicides. Herbicides were applied when the plants had 6-8 leaves that were at a height of 8 cm. At the end of the evaluations, 28 days after application, multiple resistance to paraquat, glyphosate, and chlorimuron was observed, with resistance factors (RF50) for the control of 7.43, 3.58, and 14.35 and for the reduction of dry mass of 2.65, 2.79, and 11.31, respectively. All the established criteria for demonstrating new cases of weed resistance were met; thus, the first case worldwide of a Conyza species with resistance to herbicides with three different mechanisms of action was confirmed.

Herbicide Resistance in Plants

Herbicide resistance in weeds is perhaps the most prominent research area within the discipline of weed science today. Incidence, management challenges, and the cost of multiple-resistant weed populations are continually increasing worldwide. Crop cultivars with multiple herbicide-resistance traits are being rapidly adopted by growers and land managers to keep ahead of the weed resistance tsunami. This Special Issue of Plants comprises papers that describe the current status and future outlook of herbicide resistance research and development in weedy and domestic plants, with topics covering the full spectrum from resistance mechanisms to resistance management. The unifying framework for this Special issue, is the challenge initially posed to all of the contributors: what are the (potential) implications for herbicide resistance management?

THE PROBLEM OF WEED RESISTANCE TO HERBICIDES AND THE ECONOMIC EFFICIENCY OF WHEAT PROTECTION ON THE EXAMPLE OF A LARGE-SCALE AGRICULTURAL FARM

The main purpose of the article is to assess the economic efficiency of wheat protection in conditions of the occurrence of weed resistance to herbicides in a selected large-scale farm (case study). In modern agriculture, especially in large-scale farms using monoculture, zero tillage and intensive chemical protection, the emerging phenomenon of weed resistance to herbicides is a cause of ecological and economic losses. In Poland, as well as the world, the problem of weed resistance is mainly noted in the case of wheat cultivation, which is ranked first in terms of sown area. Therefore, more and more often attempts are being made to answer the question, what is the profitability of performed weed control operations with the simultaneous occurrence of herbicide resistance. Empirical research was conducted on the basis of data recorded in the book of profits and losses recorded by the farm owner in 2014-2018. The collected data was developed using economic analysis and statistical methods. It was found that, in the examined period, due to the growing problem of the presence of resistant weeds, the use of products to control them increased and the costs of protecting wheat cultivation also increased. The low effectiveness of chemical weed control treatments resulted in a change in the structure of crops in the researched farm in the last year of the study.