As agriculture progresses, pests naturally adapt, sometimes developing resistance to traditional control methods like pesticides. This phenomenon, known as pesticide resistance, reflects the dynamic nature of farming systems and calls for innovative pest management strategies.
According to Hiresh Ramanand, a CropLife stewardship specialist, resistance occurs when pests in a population undergo inheritable changes that allow them to survive pesticide treatments.
“This resistance often results from the continuous use of the same or similar pesticides without rotation, or the incorrect application of dosages.
“Contrary to the common belief that individual pests mutate, it is the entire population within a particular location that evolves over time. A small proportion of pests may initially survive pesticide exposure due to their genetic makeup. These survivors reproduce, passing on their resistance traits, leading to a population that is less susceptible to the pesticide and this is known as a sensitivity shift,” he said.
Impact on the tomato industry
Ramanand explained that in the tomato industry, most tomato growers suspect resistance with regards to the tomato leaf miner, which is a major concern given this species’ short life cycle, high reproductive capacity, and resistance history.
“Although there is an ongoing scientific study in this regard, at this stage there are no documented records of registered pesticides that have been confirmed to be ineffective against this pest in South Africa,” he said.
Ramanand added that while there have been many reports about the lack of efficacy of products, reports were largely due to incorrect application and not adhering to label instructions, in addition to faulty spray equipment and incorrect calibration.
“In general, resistance developing in pest populations that target other agricultural commodities will not be an issue provided label application instructions and resistance management guidelines are thoroughly followed,” he said.
Integrated pest management key
To combat pesticide resistance, Ramanand advised farmers to adopt integrated pest management (IPM) strategies.
He emphasised the importance of not spraying pesticides until pests reach an economic threshold level, as determined by pest management consultants. Automatic spraying based on sightings can exacerbate resistance and lead to unnecessary expenses.
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“It is important to adhere to label instructions pertaining to resistance management guidelines of pesticide products for pests that are prone to developing resistance. For example, if the label of a product instructs that the product be applied twice in a block and then must be rotated with a suitable registered different mode of action group product for subsequent sprays, this must be adhered to.
“Reading labels, seeking expert advice when unsure, and adhering to stewardship principles are crucial when it comes to managing pesticide resistance,” Ramanand recommended.
Impact on farmers
Potato farmer CT Van Der Merwe shared the same sentiments as Ramanand and highlighted the importance of changing pesticide products frequently and using different methods to target various growth stages of pests.
He believes in the use of biological or organic products, which show promising results with zero resistance and residue.
“The bigger issue would not be that there is a pest or disease on the farm, although, production is challenged and product availability will drop, but this means that prices will increase. The main problem here is the fact that due to high demand and low supply, prices increase and consumers are immediately affected.
“As soon as the supply drops because of pests and diseases, prices will automatically increase,” he said.
For Zweli Mhlongo, a sugarcane farmer from KwaZulu-Natal, thinking ahead has helped him avoid the risks that come with pesticide resistance.
“On my farm, everything is going very well because last month I sprayed with weed killer to assist with weeds that usually come in winter,” he said.
Mhlongo shared that during winter there tends to be more pest resistance to pesticides because of the change of season and temperatures.
“Winter usually does have a bad impact on pests and at the moment we are approaching winter, less rain and no heat, while at the same time, the crops are bundling; that is why resistance is a common thing for farmers,” he said.
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