Resistance to phytosanitary products is one of the most significant challenges facing modern agriculture, especially in recent decades due to the pressures exerted by climate change and the increasing emergence of pests. To protect crops from pests, diseases, and weeds, various plant protection products such as insecticides, herbicides, and fungicides are commonly used. However, the lack of options and the repetitive use of these products have led to a concerning phenomenon: pest resistance to these chemicals. In this article, we will explore what resistance to plant protection products is, how it develops, its consequences, and the strategies for effectively managing it. Additionally, we will provide you with some digital tools to assist you in your daily activities.
# # # What is Pesticide Resistance? # # #
Resistance to phytosanitary products is defined, according to FRAC, as the ability of an organism to become less susceptible or even immune to a dose of a plant protection product that would normally be lethal. This resistance can develop in insects, weeds, fungi, and other pathogens that affect crops. Over time, and after repeated exposure to a specific plant protection product, a population of pests can become less susceptible or even completely immune to the product.
What is FRAC? The Fungicide Resistance Action Committee (FRAC) is an organization that monitors and promotes practices to manage and prevent fungicide resistance.
And you may be wondering, how does this happen? In summary, it occurs just as shown in the video.
# # # Mechanisms of Development of Resistance to Phytosanitary Products # # #
Resistance to phytosanitary products is an evolutionary process that occurs through natural selection. Here, we will analyze how this occurs:
Initial Genetic Variability: In any population of a pest, there is natural genetic variability. Some of these variations may make certain individuals less susceptible to a specific phytosanitary products.
Selection Through the Use of Phytosanitary Products: When a phytosanitary products is applied, the more susceptible individuals die, while those with resistance survive. These resistant individuals reproduce, passing their resistant genes to the next generation. In the end, we obtain a population of resistant individuals.
Increase in the Frequency of Resistant Genes: With each application of plant protection products, the proportion of resistant individuals in the population increases, as the susceptible ones are eliminated while the resistant ones survive and reproduce.
Genetic Mechanisms of Resistance: Resistance mechanisms can be monogenic (controlled by a single gene) or polygenic (controlled by multiple genes). Monogenic resistance can arise quickly, especially if a single gene confers high resistance. Polygenic resistance usually develops more slowly, as it involves the accumulation of multiple resistance genes.
# # # Factors that contribute to the development of resistance to phytosanitary products # # #
Resistance to phytosanitary products does not occur by chance, there are factors that promote and accelerate its development:
Repetitive and Monotonous Use of Plant Protection Products: This is the main factor. The repeated application of the same plant protection product or others with similar modes of action promotes the selection of resistant individuals. For example, the continuous use of a specific herbicide can result in weeds that no longer respond to that herbicide.
Application of Sublethal Doses: Applying doses lower than the recommended levels may not completely eliminate the pest population, allowing individuals with partial resistance to survive and reproduce.
Monocultures and Lack of Crop Diversity: The absence of crop rotation can maintain pest populations in an environment favorable for their proliferation, increasing the risk of selection for resistance.
Ineffective Pest Control: Inadequate pest management practices, such as lack of regular monitoring and late detection of resistance, can contribute to the development and spread of resistance.
# # # Consequences of Resistance to Pesticides # # #
Resistance to pesticides has major implications for agriculture, the environment and the economy. The main effects are:
Loss of Efficacy of Plant Protection Products: As more pests develop resistance, plant protection products lose their effectiveness, which can lead to increased crop losses and a decline in the quality of agricultural products.
Increase in Production Costs: To combat resistance, farmers may be forced to use higher doses of plant protection products, apply more expensive alternative products, or switch between more products, resulting in increased production costs.
Environmental and Health Impacts: The excessive use of plant protection products can have harmful effects on the environment, including soil and water contamination and the elimination of non-target species, such as pollinators, predatory insects, biocontrol agents, and other beneficial organisms. Furthermore, prolonged exposure to high levels of chemicals can have adverse effects on human health.
Development of Cross-Resistance: Cross-resistance occurs when a population of pests develops resistance to several plant protection products with similar modes of action, further reducing the available control options and complicating resistance management..
# # # What is Crusader Resistance? # # #
Cross-resistance is a phenomenon in which a pest develops resistance to several plant protection products that share a similar mode of action, even if it has only been exposed to one of them. This type of resistance further complicates pest management, as it significantly limits the options of chemical products that can be effectively used to control the same pest.
Examples of Cross Resistance
Insects and Pyrethroids: Insects have developed cross-resistance to several pyrethroids due to mutations in the sodium channels of the nervous system, which are the primary targets of this group of insecticides. Once this mutation occurs, all pyrethroids become ineffective, as they can no longer bind properly to their site of action.
Fungi and DMI Fungicides: This is one of the major examples of cross-resistance. In the realm of fungicides, *Botrytis cinerea* and other pathogenic fungi have exhibited cross-resistance to demethylation-inhibiting fungicides (DMI), such as tebuconazole and propiconazole. A alteration in the target enzyme (C14-demethylase) can reduce the effectiveness of all DMI fungicides, significantly complicating the control of fungal diseases.
# # # Strategies for Managing Resistance to Pesticides # # #
To address the problem of resistance to pesticides, a proactive and multifaceted approach is essential. Some key strategies include:
Rotation of pesticides: Rotating pesticides with different mechanisms of action (MoA) can help reduce selection pressure on a pest population, decreasing the likelihood of resistance developing. This means avoiding repetitive use of the same or similar products and instead alternating between different classes of pesticides with different modes of action. With our FungiRES tool you can search for all those products with which you can alternate your treatment according to their MoA and their ease of resistance development.
The FRAC classifies fungicides into different groups according to their mode of action (MOA). Modes of action refer to how the fungicide affects the pathogen at a biochemical level. Each group has a numerical code that makes it easier to identify and allows producers and agronomic advisors to implement effective product rotation strategies. Typically, this code can be found on the product label, but you can also consult it in our FungiRES tool.
Use of Pesticide Mixtures: Another effective strategy is the use of pesticide mixtures that contain two or more active ingredients with different modes of action. Mixtures can target multiple sites in the pest organism simultaneously, making it difficult for pests to develop resistance to all components of the mixture at the same time. This strategy is especially useful when dealing with pests that have already developed resistance to certain pesticides. However, it is crucial that mixtures are used carefully and only when necessary to prevent the development of multiple resistance. Furthermore, the components of the mixture should be selected in such a way that their modes of action are truly different and do not share a common resistance base or are not related.
Implementation of Integrated Pest Management (IPM): Integrated Pest Management (IPM) is an approach that combines various control methods, such as biological, cultural, mechanical, and chemical, to manage pests sustainably. By reducing reliance on chemical pesticides, IPM can decrease the selection pressure for resistance.
Use of Appropriate Doses and Correct Applications: It is crucial to apply pesticides at the recommended doses and at the right times to ensure their effectiveness. Using incorrect doses can not only be ineffective but also contribute to the development of resistance. It is important to follow the manufacturer's instructions and the recommendations of pest management experts.
If you need to calculate the correct amount of pesticide, visit our Phytosanitary Calculator: Link Phytosanitary Calculator
Regular Monitoring and Early Detection: Constant monitoring of pest populations and conducting sensitivity tests for pesticides are essential for detecting resistance in its early stages. Early detection allows farmers to adjust their management strategies before resistance becomes a widespread problem.
Visit our tool idMicrobe (Link), our pest diagnostic tool that will help you identify what disease your plants have and consult professional treatments to combat it.
Promotion of Crop Diversity: Crop rotation and diversification help reduce the incidence of pests and decrease the risk of resistance development. How? If we have a crop affected by a pathogen and we rotate it with another type of crop that is not susceptible to that disease, we will reduce the presence of the pathogen in the soil and the risk of resistance emergence. Additionally, by interspersing legume planting among crops, we will enhance the presence and increase beneficial soil microorganisms that help us combat pests.
# # # Examples of Resistance in Agricultural Pests # # #
Example 1: Insecticide Resistance in the Fall Armyworm (Spodoptera frugiperda): The fall armyworm is a devastating pest that affects a wide variety of crops, including corn, rice, and soybeans. The extensive use of these insecticides has led to an increase in the frequency of resistant individuals within the fall armyworm populations.
Example 2: Resistance to Fungicides in Botrytis cinerea. Botrytis cinerea is known for developing resistance to multiple fungicides, including quinone outside inhibitors (QoI) and demethylation inhibitors (DMI). This fungus can infect a wide range of crops, from strawberries to tomatoes and grapes, causing significant losses. Resistance to fungicides in Botrytis cinerea has primarily developed due to the repeated use of the same chemical products over several consecutive seasons.
# # # Future of Pesticide Resistance Management # # #
Looking ahead, managing resistance to plant protection products will require a global and collaborative approach involving farmers, researchers, the agrochemical industry, and policymakers. Some key areas of focus will include:
Development of New Technologies and Pesticides: Research and development of new pesticides with novel modes of action will be crucial to staying one step ahead of resistant pests. Additionally, genetic editing technologies, such as CRISPR, offer opportunities to develop crops that are more resistant to pests and diseases.
Promotion of Precision Agriculture: Precision agriculture, which utilizes advanced technology to monitor and manage crops more effectively, can help optimize the use of pesticides and reduce the risk of developing resistance. This includes the use of drones, sensors, and data analysis to apply pesticides only when and where they are needed.
Analysis of Pesticide Efficacy: This is one of the best tools for selecting the right pesticide. At the first signs of infection, laboratory analyses are conducted, like those we perform at ZeriMar Laboratoire, to determine which pesticides on the market are effective and which are not. This way, resistance is avoided, and the appropriate product is applied.
Resistance test of Botrytis cinerea against different fungicides Strengthening Monitoring and Surveillance Networks: Establishing and maintaining robust monitoring and surveillance networks to detect resistance to pesticides is crucial. This allows for a quick and effective response to adjust management strategies before resistance becomes a significant problem.
Pesticide resistance poses a significant threat to sustainable agriculture and global food security. However, with a clear understanding of how resistance develops and a proactive management approach, it is possible to mitigate its effects. Adopting integrated management strategies, investing in research and development, and promoting ongoing education are key steps to ensure that pesticides remain effective tools for crop protection. Global collaboration and commitment will be essential to effectively tackle this challenge and secure a sustainable future for agriculture.
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