Lawn Worm and Wormcast on Lawns & Turf

Lawn worm and worm casts are one of the most common problems during autumn and winter period when the soil is wet.

In the UK, several lawn pests can be problematic for gardeners. Some of the most common lawn pests include:

• Leatherjackets: These are the larvae of crane flies or daddy longlegs. They feed on grass roots, leading to yellow patches on the lawn.

• Chafer Grubs: These are the larvae of chafer beetles. Like leatherjackets, they feed on grass roots. Birds and animals, like badgers and foxes, might dig up the lawn to eat these grubs, causing further damage.

• Frit Flies: Their larvae, known as grass maggots, feed on the stems of grass plants near the soil surface.

• Earthworms. Worms don’t harm the turf itself; in fact, they are generally seen as beneficial because their burrowing actions help drain the soil. However, the issue arises with the small mounds of soil they eject onto the lawn’s surface. When these mounds are flattened by feet or lawnmower wheels, they can create an uneven lawn surface. The grasses under these compressed mounds die, and the damp, sticky soil left behind provides an ideal environment for weed seeds to germinate. Additionally, a high concentration of earthworms might attract moles.

Insect Larvae

The most damaging pests for lawns are the larvae of crane flies and chafer beetles. Crane fly larvae, also known as leatherjackets, hatch in the autumn and feed on the roots and stems of plants in the spring. This leads to patches of yellowed or browned grass. Aerating the soil can help prevent crane fly infestations. The curved larvae of chafer beetles eat grass roots in the spring and summer. The affected grass turns brown and can be easily pulled from the soil. Partial protection against chafer beetles can be achieved by rolling the soil in spring. The most effective method to eliminate all types of larvae is the application of insecticides.

What is worm-casts on lawn?

Worm casts on a lawn refer to the small mounds of soil or mud produced by earthworms as they digest organic matter and excrete the digested soil. These casts are essentially the waste products of earthworms.

1. Composition: Worm casts are composed of soil, organic matter, and worm mucus. They are richer in available nutrients than the surrounding soil because they’ve been processed through the worm’s digestive system. This makes worm casts beneficial for the soil in terms of fertility.
2. Appearance: They appear as small, clumpy mounds of soil on the surface of the lawn. While they’re beneficial for the soil’s structure and fertility, they can be seen as unsightly on well-maintained lawns.
3. Impact on Lawn: While the presence of earthworms is generally an indicator of healthy soil, worm casts can be problematic for lawn aesthetics. They can smother the grass, leading to thin or bare patches, and provide a seedbed for weeds. The mounds can also become hard when dried, causing an uneven lawn surface. Additionally, when mown over, they can smear and create a muddy surface, especially when wet.

Precautions to reduce harm from earthworms:

Managing worm casts can be a bit challenging because earthworms are beneficial for the soil. Some methods to deal with worm casts include:

• Always remove mown grass from the lawn.
• Sweep off worm casts from the lawn surface.
• Try to increase the soil’s acidity: mulch the lawn with peat, use fertilizers (like ammonium sulfate), and avoid adding lime to the soil.
• Brushing off the casts when they are dry, using a stiff brush or the back of a rake.
• Regular mowing can help disperse the casts.
• Avoid over-watering, as moist conditions encourage worm activity.
• There are also some products on the market that claim to deter worms, but their efficacy varies and might impact the beneficial worm population.

Conditions in the lawn that favour worms

Earthworms favour the following conditions in lawns.

• Wet and warm conditions – As we are experiencing more rainfall in the UK, earthworms are becoming more of a problem on lawns. In fact the whole climate has become wetter and warmer, causing problems with casting worms. We have also been experiencing fewer hard frosts which drive the worms deeper underground thus reducing any worm cast problems.
• Favourable soil types – Worms favour heavier clay and loam soils which have a high thatch and organic matter content for the worms to feed on. However they can still be present in lighter free draining sand based soils. However they are less of a problem in lighter soils as the worm-casts are easily dispersed without smearing the surface and creating a muddy surface.
• Ideal pH – The majority of earthworms prefer a neutral to alkaline (high pH) soil however some types of worms can survive in acidic soils. The pH is a scale used to measure how acidic or alkaline a soil is.
• High organic matter content – Worms will always favour a soil with a high organic matter content as this is their food source.

How to Deal with Lawn Worm?

When dealing with lawn pests such as Leatherjackets (larvae of the crane fly or daddy longlegs) and Chafer Grubs (larvae of chafer beetles), a combination of cultural and chemical controls is often recommended. Below are some chemical treatments and biological controls often used against these pests:

1. Biological Controls:
   • Nematodes: These are microscopic worms that are natural predators of leatherjackets and chafer grubs. There are specific types of nematodes for each pest: Steinernema feltiae for leatherjackets and Heterorhabditis bacteriophora for chafer grubs. They are watered into the lawn and actively seek out and kill the larvae. They work best in moist, warm soil conditions.
2. Chemical Insecticides:
   • Imidacloprid: This is a systemic insecticide that can be effective against chafer grubs when applied correctly. However, it’s essential to be aware of the environmental implications and potential harm to non-target species.
   • Acelepryn: This insecticide can target both leatherjackets and chafer grubs. It has been granted emergency authorizations in the UK in certain situations due to its lower impact on non-target species.
3. Cultural Controls:
   • Regularly aerating the lawn can help disrupt the life cycle of these pests.
   • Encouraging natural predators like birds and hedgehogs, which eat these larvae, can be beneficial.
   • Ensuring a healthy lawn through proper fertilization and mowing can help the grass withstand and recover from pest damage more effectively.

It’s always crucial to carefully read and follow label instructions when applying any chemical treatments. In addition, consider the potential environmental impacts and explore alternative methods where possible. The best approach often involves a combination of cultural, biological, and, if necessary, chemical controls.

Management of worms in lawns

Many years ago chemicals such as chlordane were used very successfully to control worms but were recently banned. The only chemical for use on worms at present is a product called Carbendazim, this product is actually a fungicide with worm control properties.

Carbendazim is widely used in the fine turf industry on sports grounds and golf courses but the product can’t be purchased for home use. However there are various cultural methods you can employee to try and discourage worm activity in your lawn.

• Lower the pH level – By gradually lowering the soil pH you will help discourage worms as they prefer a higher pH. You can do this by applying acidifying products and fertilisers such as sulphate of iron and lawn sand. A light monthly application of sulphate of iron at a rate of 8g/m2 during the autumn and winter months may reduce worm numbers. This product can be purchased from garden centers and it is quite cheap. It is mixed in hot water and applied with a sprayer or watering can. Ensure it is mixed thoroughly as it can block spray nozzles or you can put it through a filter before filling your sprayer. Be careful when using this product as it can stain clothes and concrete pathways. Please visit our Sulphate of Iron information page for advice on this product.
• Reduce the thatch or organic matter content – If thatch build up (thatch = organic matter) is a problem in you lawn reducing it would help lower the worm population. Scarifying (ideally during the autumn) will remove excess thatch from the lawn. The removal of leaves from the lawn during late summer and by boxing of grass clipping when the lawn is mown will all help prevent thatch accumulation.
• Manual removal of worm-casts – Tools and implements such as brushes, switches and drag mats are available for the removal of worm-casts. On heavy clay soil make sure that the worm-casts have dried sufficiently before removing or they will smear the grass.
• Raising the height of cut on the mower – During periods of worm activity it would be beneficial to raise the height of cut on the mower. This leaves the grass longer and helps reduce the smearing effect.

Unfortunately there are no real effective methods left to totally remove earthworms and worm-casts on lawns. The most effective chemicals have now been banned for sometime now. We are now left with the cultural methods to try and reduce earthworm numbers, and these may not prove very effective if you have a severe problem.