Common Lawn Diseases, Pests, and Their Management

A lush, green lawn is the pride of any garden – but keeping it that way is not always easy. Lawns face a constant battle against diseases, pests, and environmental stresses that can turn a beautiful turf into a patchy, discoloured mess. From fungal infections that spread silently through the soil to insects that chew through grass roots underground, the threats are diverse and often hard to spot until significant damage has already occurred. The good news? Most lawn problems are manageable when you know what to look for and how to respond. Let’s break down the most common lawn diseases, pests, and other problems – and what you can do about each one.

Common fungal diseases that affect lawns 🔗

Fungal diseases are among the most frequent causes of lawn deterioration. They thrive in specific weather conditions and can spread rapidly if left unchecked. Understanding the symptoms and triggers of these diseases is the first step toward effective control.

Fusarium patch (snow mould) 🔗

Fusarium patch is one of the most recognisable lawn diseases. It is caused by the fungus Microdochium nivale and typically appears as circular patches of bleached, straw-coloured grass on the lawn surface. These patches can range from a few centimetres to several feet across.

The disease is most active during cool, damp conditions – particularly in autumn, winter, and early spring. It can also develop under snow cover, which is why it’s commonly called snow mould. When the grass is wet, you may notice white or pinkish cotton-like fungal growth (mycelium) on the turf surface. Fusarium particularly targets annual meadow grass (Poa annua), though it can affect most grass types.

Several factors increase the risk of Fusarium patch: excessive thatch buildup, soil compaction, poor drainage, high humidity, and lack of airflow across the turf. Lawns that receive heavy nitrogen fertilisation late in the season are also more vulnerable, as the soft, lush growth is easily attacked.

Management: Preventive measures are more effective than curative treatments. Regular scarification to reduce thatch, aeration to improve drainage, and avoiding overwatering are all essential cultural practices. If infection occurs, affected areas should be kept as dry as possible, and fungicide applications – particularly those containing azoxystrobin or propiconazole – can help control the spread. Damaged turf will typically need reseeding in spring once conditions improve.

Fairy rings 🔗

Fairy rings are among the most distinctive lawn problems you’ll encounter. They appear as circular or semi-circular patterns on the lawn – sometimes as dark green rings of fast-growing grass, sometimes as rings of dead turf, and occasionally as circles of mushrooms or toadstools.

These rings are caused by various species of basidiomycete fungi, with Marasmius oreades being one of the most damaging. The fungi colonise the soil or thatch layer, feeding on organic matter and expanding outward at roughly 30 cm per year. As the fungal colony breaks down organic material, it releases nitrogen – producing that characteristic ring of darker green grass. However, the fungal mycelium can also make the soil hydrophobic (water-repellent), which starves the turf of moisture and leads to dead patches.

Fairy rings are classified into three main types. Type 1 produces rings of dead or wilted grass with dry soil beneath – the most damaging form. Type 2 shows dark green rings of stimulated growth without dead grass. Type 3 produces rings of mushrooms with little visible effect on the turf itself.

Management: Fairy rings are notoriously difficult to control. For Type 1 rings, aerating the affected area and applying a wetting agent helps water penetrate the hydrophobic soil. Type 2 rings can be masked by applying nitrogen fertiliser evenly across the lawn. For severe infestations, fungicide applications of azoxystrobin have shown good results when used properly. In extreme cases, physically removing the infected soil and turf – along with the white mycelial mass – may be necessary. Regular dethatching and proper fertilisation help prevent fairy rings from establishing in the first place.

Other notable lawn diseases 🔗

Red thread is extremely common, especially in lawns deficient in nitrogen. It appears as patches of brown or bleached grass with distinctive reddish-pink fungal threads visible on the blades during humid weather. Improving nitrogen levels through balanced fertilisation usually resolves the issue.

Dollar spot causes small, silver-dollar-sized patches of pale grass that can merge into larger irregular areas during humid conditions. It thrives when lawns are stressed by low mowing heights, drought, or low nitrogen levels. Brown patch creates large circular areas of dead grass with a distinctive darker ring around the edges and is most active in warm, humid weather. Both diseases respond well to improved cultural practices and, where necessary, targeted fungicide use.

Common lawn pests and their damage 🔗

While diseases attack the grass plant directly, pests cause damage through feeding, tunnelling, or disrupting the soil structure. Identifying the culprit correctly is crucial – treating for the wrong pest wastes time and money.

White grubs 🔗

White grubs are the larval stage of various scarab beetles, including Japanese beetles and European chafers. These C-shaped, cream-coloured larvae feed on grass roots just below the soil surface, causing patches of turf that turn brown, feel spongy underfoot, and can be peeled back like a carpet.

Grub damage typically peaks in late summer and early fall when the larvae are actively feeding. Secondary damage often follows – birds, moles, skunks, and raccoons dig up the lawn to feed on grubs, making the problem worse. However, animal digging alone is not always a reliable sign of grub infestation, as these animals also feed on earthworms and other soil organisms.

Management: Start by confirming the infestation. Dig a one-foot-square section of turf about 5-8 cm deep in the affected area. A healthy lawn can tolerate up to 5-10 grubs per square foot without visible damage. If numbers exceed this threshold, treatment is warranted. Preventive insecticides containing chlorantraniliprole or imidacloprid, applied in early to mid-summer before grubs hatch, are the most effective chemical option. For late-season curative treatment, products containing carbaryl or trichlorfon can be used, though their effectiveness varies. Biological controls such as insect-parasitic nematodes also offer a less toxic alternative.

Ants 🔗

Ants are a common nuisance in lawns. While they don’t directly feed on grass, their nest-building activities can cause significant disruption. Ant colonies loosen the soil around grass roots, create uneven mound-like surfaces, and can smother grass in the immediate area of the nest. Fire ants are particularly problematic, building large dome-shaped mounds that kill surrounding grass and pose a safety risk to people and pets.

Management: For common garden ants, regularly brushing away soil mounds and watering the area can discourage nesting. For fire ants, broadcast bait treatments applied in spring and fall are the most cost-effective approach. Individual mounds can be treated with liquid drenches or granular contact insecticides. Products containing hydramethylnon or spinosad are commonly used for long-term fire ant control.

Earthworms 🔗

Earthworms are generally beneficial – they aerate the soil, improve drainage, and break down organic matter. However, in fine-turf areas like ornamental lawns, their castings (small mounds of excreted soil) can be a nuisance. Earthworm casts create an uneven surface, smother grass beneath them, and provide a seedbed for weeds.

Management: Complete elimination of earthworms is neither practical nor advisable given their ecological benefits. Instead, manage their impact by regularly brushing or sweeping casts when dry, reducing excess organic matter on the lawn surface, and improving surface drainage. Acidic soil conditions tend to discourage earthworm activity, though deliberate acidification is rarely recommended as a primary control measure.

Other lawn pests 🔗

Chinch bugs are sap-sucking insects that pierce grass blades and extract plant juices while simultaneously injecting a substance that prevents the grass from absorbing water. This leads to yellowing patches that eventually die. They are most active in hot, dry conditions. Armyworms are caterpillars that can strip large areas of grass down to soil level in a matter of days. Biological controls like Bacillus thuringiensis (Bt) and spinosad are effective, low-toxicity options for caterpillar pests. Moles tunnel through lawns in search of grubs and earthworms, leaving raised ridges and collapsing soil behind them. Controlling their food source (particularly grubs) can help reduce mole activity.

Frost injury and other environmental problems 🔗

Not all lawn damage comes from living organisms. Environmental stresses – particularly frost and extreme cold – can cause significant harm to turf.

How frost damages your lawn 🔗

Frost forms when temperatures at ground level drop below freezing, causing moisture on and within grass blades to freeze. The water inside plant cells expands as it freezes, which can rupture cell walls – especially if the frozen grass is walked on or mowed. This mechanical damage is one of the most common causes of frost injury in lawns.

Symptoms include brown or yellow discolouration, brittle and broken blades, and in severe cases, death of the grass crown (the growing point of the plant). If temperatures suddenly fall below -6°C (about 20°F), permanent damage may occur – the grass may appear wilted, mat down to the ground, and even develop a foul smell.

A related problem is winter desiccation, where cold, dry winds strip moisture from grass blades while the frozen ground prevents roots from replacing it. This is particularly common on exposed, elevated areas with little snow cover. Crown hydration is another concern – a warm spell followed by a sudden refreeze causes hydrated plant tissues to rupture, potentially killing the grass.

Preventing and repairing frost damage 🔗

The most effective preventive measure is simple: stay off frosted grass. Walking, driving, or mowing on frozen turf compresses the brittle blades and dramatically increases damage. Wait until the frost melts completely before resuming normal lawn activity.

Other preventive steps include deep watering the evening before an expected frost – the slow evaporation creates enough heat to keep blade temperatures slightly above freezing. Avoid late-season heavy nitrogen fertilisation, as lush, succulent growth is more prone to freeze injury. Instead, a balanced autumn fertiliser programme focused on potassium helps build cold tolerance.

After winter, assess the damage before taking action. Give your lawn time – grass that appears dead may simply be dormant and can recover once temperatures rise. For areas that don’t bounce back, remove dead material, scarify the area, and overseed once soil temperatures reach around 6-8°C. Light fertilisation in early spring encourages recovery, and core aeration improves root health in compacted areas affected by snow or ice.

An integrated approach to lawn health 🔗

The best defence against lawn diseases, pests, and environmental damage is a healthy, well-maintained lawn. Here are the key practices that underpin effective prevention:

Regular mowing at the correct height keeps grass vigorous without stressing it. Cutting too short weakens the turf and makes it vulnerable to both diseases and pests. Proper watering – deep and infrequent rather than light and daily – encourages deep root growth and reduces the damp surface conditions that favour fungal diseases.

Balanced fertilisation ensures grass has the nutrients it needs to resist disease and recover from damage. Nitrogen-deficient lawns are particularly susceptible to red thread, dollar spot, and other fungal infections. Aeration and dethatching improve air circulation, water penetration, and soil health – all of which reduce the risk of both diseases and pest infestations.

Regular monitoring is perhaps the most important practice of all. Walk your lawn frequently and look for early signs of trouble – unusual patches, discolouration, mushrooms, insect activity, or changes in texture. Early detection allows for targeted intervention before problems become severe. When chemical treatments are needed, always opt for the least toxic option effective against the specific problem, and use pesticides only as a last resort after cultural practices have been tried.

What do you think? Have you noticed any unusual patches, rings, or pest activity on your lawn recently – and if so, what was your first step in diagnosing the problem? How do you balance the use of chemical treatments with cultural practices in your own lawn care routine?

References

1. https://www.rhs.org.uk/biodiversity/fairy-rings
2. https://www.topgrass.net/lawn_advice/a_guide_to_lawn_diseases.aspx
3. https://ipm.ucanr.edu/agriculture/turfgrass/fairy-ring/
4. https://extension.unh.edu/resource/insect-pests-home-lawns-fact-sheet
5. https://extension.unh.edu/blog/2019/09/how-do-i-treat-grubs-my-lawn
6. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7476.html
7. https://extension.msstate.edu/publications/control-insect-pests-and-around-the-home-lawn
8. https://www.advancedturf.com/resources/preventing-lawn-damage-from-frost/
9. https://gardeningsolutions.ifas.ufl.edu/lawns/problems-and-solutions/cold-damage-to-turf/
10. https://turf.umn.edu/news/damaged-lawns-steps-bringing-some-life-back