Ask any New Zealand farmer what threatens pasture performance and grass grub and Argentine stem weevil will be near the top of the list. These pests can strip a paddock in weeks, reduce feed quality, and cost serious money in lost production. Chemical control has long been the primary defence, but research is showing a more durable approach: working with soil biology to reduce pest pressure over time.
Fertilizer NZ research shows healthy soils are more than nutrient stores, they act as a first line of defence. Beneficial microbes and fungi compete with harmful organisms and help suppress pest populations. When soil is biologically active and balanced, pests find it harder to establish and survive.
Grass grub provides a clear example. Conventional control relies on well-timed insecticide applications, yet trials indicate paddocks with active microbial populations can have lower grub survival even without additional treatments. Certain fungi and bacteria attack larvae directly or out compete them for space and resources. Argentine stem weevil numbers also decline where soil biological activity is strong.
Building this natural defence begins with maintaining conditions that support soil life. Minimising excessive cultivation helps protect soil structure and microbial habitat, while maintaining organic matter provides the energy source that soil organisms rely on. Avoiding prolonged bare ground and supporting pasture cover further protects biological activity. Biological fertilisers can strengthen this system by introducing beneficial organisms. Microbes such as Beauveria, Metarhizium, and Bacillus are known for their pest-suppressing properties. They are not quick fixes and require suitable soil conditions, but in a well-managed system they can contribute to reduced pest pressure.
Pasture management also plays a role. Fertilizer NZ trials indicate rotation and carefully planned grazing reduce pest favourable conditions while allowing beneficial soil microbes to remain active. Strategic stock movement can help prevent grass grub populations from establishing in vulnerable areas, and maintaining dense pasture cover supports the biological processes working below ground.
Biology will not replace chemicals entirely, but it can reduce reliance, improve resilience, and strengthen pasture performance over time. These gains are seen in improved pasture growth, reduced pest damage, and a more stable farm system.
Pests will always be part of farming systems, but they do not need to dominate. With science-backed practices, farmers can create conditions where natural processes contribute to control. This approach requires observation and consistency, but it leads to paddocks that are stronger, more resilient, and easier to manage.
Before making next season’s control decisions, consider what is happening below the surface. Supporting the biological life in your soil may be one of the most effective ways to reduce pest pressure and protect pasture production.
Soil biology to reduce pest pressure