SIX WAYS TO GET RID OF GRASS GRUB NATURALLY
Grass grubs can be a major hindrance to your grass at this time of year, but you can deal with them without toxic chemicals.
If you begin to notice patches of brown, dead grass in your lawn or pasture this month, you may have a grass grub infestation. A type of scarab beetle endemic to New Zealand, the grass grub (Costelytra giveni) is one of the most common insects in New Zealand. In its larvae form, it eats the roots of grasses and vegetation, resulting in extensive damage especially at this time of year.
The grass grub life cycle
The adult beetles emerge from the soil in early summer, typically between December and January, and begin to mate and lay their eggs. The eggs hatch into C-shaped larvae, which undergo three stages of development (instars) before pupation, feeding on the roots of grasses – particularly clover – along the way. They inflict the most damage to grass in their third instar phase, as this is their final feeding stage before winter. The resulting patches of brown or dead grass can increase in size over time, leading to a complete loss of grass and vegetation in the affected areas if left unchecked.
While conventional treatments involve sythentic insecticides and chemicals that may linger in your soil, there are effective, low-tox ways to get rid of, or deter, grass grubs.
Neem
Neem – or more specifically the extract of the seeds of the neem tree (Azadirachta indica) – is a common way of preventing grass grub infestation. The active compound – azadirachtin – works by disrupting the feeding and breeding cycles of the beetles, making it difficult for them to survive and reproduce. It typically comes in three forms: sprays, cakes or granules. These are available to buy online or from most garden centres. Neem, however, may harm other beneficial insects.
Nematodes
are microscopic worms that will infect and kill the larvae of the beetle. They are available to buy from many garden centres and online stores. To use nematodes, apply them to the affected areas of your lawn or garden according to the product instructions. Nematodes are effective, but it may take several applications to see results. Using nematodes is considered safe for humans, pets and non-target insects.
Promote healthy soil
Because the larvae prefer to feed on weakened or stressed plants, improving the health of your soil and providing the plants with the nutrients they need can make them more resilient to infestations. You can improve soil health by adding compost, organic matter, and using natural fertilisers.
Encourage beneficial insects
Encouraging beneficial insects in your garden can also help to control Costelytra giveni. Predatory insects such as ground beetles, centipedes, and spiders will prey on the larvae of the beetle. You can attract these beneficial insects by planting a variety of flowers and plants, creating habitats for them, and avoiding the use of pesticides that can harm them.
BT
Bacillus thuringiensis, or BT, is a soildwelling bacterium that can kill grubs living in your soil. When grass grubs ingest BT, it paralyses their digestive tract, causing them to gradually starve to death. BT products can be purchased at garden centres and can be applied to the soil in the form of sprays or granules.
Diatomaceous earth
Diatomaceous earth is the fossilised remains of diatoms, a type of hard-shelled plankton. It comes in a fine white powder that can kill beetles and their larvae by dehydrating them. The downside to diatomaceous earth is that it can affect and deter other beneficial insects. Apply in dry conditions and reapply after rain. Make sure to wear a mask, as the powder can irritate the lungs if inhaled.