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Curl grubs and army worms are unseen invaders in your garden. Their impact can be swift and devastating. If left unchecked, these pests can quickly damage your lawn and plants.
What are curl grubs?
Curl grubs are the larvae of various common beetles, including the African Black Beetle, Cockchafer and Christmas Beetle. They are typically white and plump, grow to about 3cm or more in size, have three pairs of legs, and have a small orange head. These grubs are extremely common in Australian gardens. Some are the larvae of native beetles. If identified as such, they should ideally be left alone if possible because native species are protected.
While most curl grubs should pose little (if any) threat to healthy plants in the garden, there are some that will devour the roots of lawn grasses, resulting in dead patches appearing in your lawn. They are also known to sometimes feed on the roots of shrubs, flowers and vegetables.
What are army worms?
Army worms are often surface dwellers on lawns and look very similar to almost any other caterpillar. They are the larvae of several different species of small moths that like to lay their eggs in grassy areas where the soil is warm and moist.
The caterpillars usually occur in large numbers, so the damage they can cause in a very short period can be quite devastating to your lawn and sometimes also to other plants in the garden. They can be difficult to eradicate completely, so persistence is needed and a range of different control techniques are usually required.
How to control curb grubs and army worms in the lawn
Curl grubs and army worms are most active in the warmer, more humid months of the year. Various “mechanical” means can be used to control them, including laying dampened newspaper, cardboard, or old carpet over the lawn at night to draw the grubs and worms to the surface, then collecting and disposing of them early next morning.
However, better control will usually be achieved by using a specifically formulated lawn insecticidal treatment seasonally. Products include:
Always read labels thoroughly and follow the instructions carefully. If recommended, wear gloves and other protective equipment. Repeat applications may be required to combat severe infestations.
Aerating the lawn before application may help any of these products penetrate into the root zone of the lawn where grubs are found.
If you do not want to use insecticides, encouraging native birds like magpies into your garden may be helpful. These birds will fossick for and eat live curl grubs. Alternatively, an application of eco-Neem may prove effective. This can be used as a soil drench on both lawns and garden beds. Read the instructions carefully, diluting and applying as directed on the label. Use protective equipment if recommended.
How to control curb grubs and army worms in garden beds
You are more likely to find curl grubs rather than army worms in garden beds, especially if you have native trees like wattles and gums growing, as these trees are hosts to many of the beetles whose larvae will hatch in the soil beneath them.
You might not even know they are in the soil until you dig it over, and then you might be amazed at the numbers you find!
Bringing them to the surface and then collecting and disposing of them is the best way to control them in garden beds. Another easy method is to drench the soil with buckets of water to which some liquid detergent has been added – they will quickly come to the surface when irritated by the soapy water. Eco-Neem may also be used in a similar way – follow the instructions on the label for the amount to use for soil drenching.
Please note that some gardeners think curl grubs may be beneficial for garden beds, as their movement through the soil helps aeration, moisture penetration and nutrient availability.
How to control curb grubs in pot plants
Curl grubs are often found in the base of pots. Pots standing on the ground (soil or paved surfaces) are attractive to beetles, who may lay their eggs in warm, moist growing mixes.
Some gardeners think curl grubs must have come in the bag of potting mix, but due to the temperatures and disturbances involved in the composting and manufacturing processes of these mixes, it is highly unlikely that viable eggs or larvae of curl grubs will be present in fresh bags. Please remember that it is not a good idea to buy and store bags of potting mix at home for more than a week or two, as there is always a risk of contamination or pest entry when bags are kept outdoors or even in the garden shed. Most potting mix bags have a row of perforations (breather holes) near the top seam, which may allow adult beetles to enter the bags if they are stored for prolonged periods.
If you discover curl grubs in a pot, the best option is to remove plants, remove any grubs present, and discard the old growing media. Then repot the plants in thoroughly cleaned pots with fresh potting mix.
As an alternative to repotting, try blocking the drainage holes in the bases of affected pots, then flooding them with water to which a small amount (a few drops) of liquid soil wetter has been added. Leave the pots to stand flooded for one or two hours. Any grubs present should float to the surface and can then be removed. Eco-Neem may also be used as a soil drench – follow the instructions on the label.
Please note that the small creamy yellow or beige spheres often seen in bagged potting mixes are not curl grub eggs. They are the beads (or prills, as they are known) of controlled-release fertiliser included in most premium-quality mixes.
If you need further assistance to help control curl grubs and army worms in your garden, please don’t hesitate to ask the community for help.
