Effective pest control in perennial crop monocultures demands a diversified approach. By Anna Mouton.
Modern agriculture has created areas of crop monocultures that are primarily managed through chemical interventions. Crop-protection specialist Dr Gideon van Zyl of ProCrop discussed the challenges posed by these monoculture agroecosystems.
Van Zyl described how monoculture agroecosystems suffer from poor biodiversity — biodiversity shrinks as monocultures expand. Low biodiversity is associated with unstable ecosystems that require regular human inputs such as spray applications. The problem with this chemical dependency is that natural predators are eliminated.
Pests thrive in monocultures thanks to low predation and abundant food and shelter. Van Zyl explained that pests are short-lived but produce many offspring which enables them to adjust quickly to single management tactics — resistance to pesticides is just one example of pests dodging control.
“In the short term, sprays are effective, but what are we going to do in the long term?” asked Van Zyl. “We’re currently losing active ingredients at a dramatic rate which puts a lot of pressure on us in terms of what we have in our pesticide arsenal.”
Pests find it hard to adapt to multiple management tactics. This is why the best strategy for combatting pests is to combine cultural and mechanical interventions with chemical and biological control.
Integrated pest management was traditionally defined as applying all available control methods to a specific agroecosystem in a way that is cost-effective and safe for humans and the environment. Van Zyl prefers the definition put forward by Marcos Kogan in a 1998 paper. Kogan sees integrated pest management as a decision-support system.
“The system should first be based on maintaining and improving profitability,” said Van Zyl. “Secondly, it needs to minimise the selection pressure of the chemicals or other measures that we use. And, thirdly, it needs to maintain environmental quality.”
Prevention is better than pesticides
Integrated pest management consists of preventative tactics and therapeutic practices. “Preventative strategies should start with creating a viable agroecosystem that will promote biological control,” stressed Van Zyl. “We need to create an environment where biological control agents can survive and thrive.”
Van Zyl shared the results of trials conducted at Bokveldskloof in the Koue Bokkeveld where the application of compost and mulch over the past two decades has improved the stability of the soil ecosystem. This has led to effective biological control of woolly apple aphid to the extent that chemical control has not been necessary since at least 2015.
Long-term sustainable pest control relies on what Van Zyl calls ecological pest management — incorporating and maintaining elements of natural ecosystems to support crop health. This includes improving soil health by reducing tillage, maintaining cover, building carbon, and regulating nutrients. Cover crops tick many of the soil-health boxes while also providing habitat for pollinators and predators.
“We need to increase our diversity richness,” said Van Zyl. “We need to try to introduce native species that can dominate these areas.”
Van Zyl advocates for proactive pest management — growers must have a plan. This starts with an annual pest and disease risk assessment in which pest pressure is reviewed for every orchard.
“The idea is to group orchards according to risk so that we can plan what strategy we are going to follow in each of those orchards,” said Van Zyl. “And secondly, to identify why we have issues in those orchards. Just by doing this, you will immediately reduce pesticide use because you are not using a blanket approach anymore.”
Growers should have a management strategy for each pest and disease on their farm — before the season starts. This should include systems for reducing pest-population densities and host susceptibility.
Van Zyl showed a management strategy for banded fruit weevil to illustrate his point. Spray applications complement other measures such as orchard skirting, trunk barriers, and bridge removal. Data on fruit damage in apple orchards demonstrate that chemical control is not significantly more effective than stem barriers and orchard skirting.
Measure before you manage
Monitoring is one of the cornerstones of integrated pest management — no battle can be won without good intelligence. “We need to monitor effectively on a fine scale so that we make sure that we get the correct information to use integrated pest management as a decision-support system,” said Van Zyl.
He noted that effective monitoring is as much about not monitoring excessively as about not monitoring enough. There is nothing to be gained by wasting time in the orchard.
Knowing the pests is essential. “You need enough well-trained personnel on your farm to identify your pests and who are good at scouting,” said Van Zyl. “It is very important that they can discern pests and predators.”
Van Zyl recommends sending personnel on monitoring courses. “We’ve got great facilities in the Western Cape that teach monitoring courses, specifically at the Koue Bokkeveld Opleidingsentrum.”
Knowing pest biology and population ecology is necessary for interpreting and responding to monitoring data. Data on pest numbers and distribution combined with environmental and other data can feed into models that inform decisions about control.
Van Zyl used codling moth as an example of how monitoring and modelling support pest management. In a low-risk orchard, mating disruption combined with early-season chemical control should remove the need for further chemical control in that season. Less spraying equals less impact on beneficial insects and the environment while also cutting costs.
In a high-risk orchard, spraying throughout the season will be necessary, combined with other strategies such as mating disruption, regular orchard sanitation, thinning in bags, and removing pupae. This should reduce pest pressure and spray applications in the following season.
Correct spray technique that limits drift is imperative. Drift is not only wasteful but also defeats the purpose of integrated pest management by killing beneficial organisms and harming the environment.
“Integrated pest management is not a method for reducing pesticide use,” said Van Zyl. “Chemical application is still the heart of the system — it forms an integral part of integrated pest management. But chemical application is not a silver bullet — don’t spray following a programme. Use a strategy to control pests.”
Image: Dr Gideon van Zyl, ProCrop. Supplied by Echo Media.