Pest or pathogen resistance is increasingly becoming a significant challenge in agriculture worldwide. Resistance happens when a pest or disease builds up a tolerance and becomes resistant to a specific chemical, making the product ineffective.
According to Irene de Bruijn, Team Lead Microbial Profiling at Koppert, resistance can occur when a grower repeatedly uses a product with the same mode of action. A mode of action is how a crop protection solution controls a pest or disease. For example, if a pesticide blocks only one characteristic of the pest, there is an increased likelihood of resistance development.
Pest and disease resistance: What is happening?
“The individual pests and diseases themselves do not become resistant, but the population adapts through small changes in their DNA. For example, when chemical-resistant pests breed, they pass their genetic makeup to their offspring, and their offspring in turn have a higher chance of being resistant to the chemical” Irene explains. “We see the most resistance in crops cultivated in a monoculture where crops are grown in large numbers with a high population of pests and diseases. The quicker the lifecycle of the pest or pathogen, the higher the likelihood for resistance.”
Why is biocontrol different?
Biocontrol is a natural form of pest and disease control, and the highly unlikely possibility of resistance is one of the key benefits of incorporating biocontrol into a comprehensive IPM strategy. Many biocontrol agents often have multiple mode of actions. Fungi, for example, can develop within pests and suffocate them. Beneficial insects and mites can predate on different life stages of a pest. They can actively seek them out in difficult-to-reach places. Each time a grower uses a different mode of action, the pest must develop a new way to counter the biocontrol.
A good example of this is Trianum (Trichoderma harzianum) which has multiple modes of action. Trianum defends the plant from soil-borne pathogens by creating a barrier around the roots and attacking pathogens via mycoparasitism. It also improves the root system through the formation of more root hairs so that water and nutrients can be taken up better. This leads to a stronger and more uniform crop and better yields. This effect is stronger when the plant is under stress and/or cultivated under less than optimum growing conditions. Trianum also reinforces the defence mechanism of the parts of the plant above ground, the so-called induced systemic resistance (ISR) and it produces compounds that degrade the fungal disease cell walls.
Irene emphasises that the key is for a grower to incorporate multiple modes of action in a resistance strategy. Biocontrol should be part of a comprehensive IPM strategy. Growers need to understand their crops and the associated diseases and pests well. “A good application strategy is very important for effective biocontrol. Growers need to know how and when to apply agents, at the right time and with the right dosage. Preventative measures like crop rotation and good hygiene will also contribute to effective biocontrol within IPM. When looking at the future role of biocontrol, especially in the light of increasing concerns about pesticide resistance in agriculture, Irene highlights that it is so important that the biocontrol industry learns from the development of resistance to chemicals. “IPM is very important, and we must develop a good strategy, ensuring that we keep providing biocontrol agents that are based on multiple modes of action. Combine different strategies and compounds, including micro and macro agents that target the same pest, but have different modes of action. This will ultimately strengthen control and limit resistance” Irene concludes.