Pink patch (Limonomyces roseipellis) is a parasitic fungus which can infect lawn grass. It often appears in conjunction with red thread lawn disease, causing similar symptoms.
The disease causes areas of grass to discolour. These are usually circular, but they can coalesce into larger areas. These patches can appear over a few days, and may stay for several weeks.
When examined, the grass looks necrotic, with leaves knitting together. The obvious pink growths protruding from the grass leaves.
Pink patch is usually easier to identify than red thread. The gelatinous, pink, spiked growths can be up to 1 cm in diameter and are a very bright pink colour. This makes them easy to see, often without even examining the grass.
Which grasses does pink patch infect?
Slender and strong creeping red fescues (festuca ssp.) are most at risk from infection. Fescue grasses are often a common species in turf. Recently laid fescue turf is at a very high risk of pink patch and red thread infection.
Perennial ryegrass (Lolium perenne sp.), bentgrasses (Agrostis spp.) and (Poa sp.) can also suffer pink patch infection.
When is the grass most at risk?
Pink patch is a parasitic fungal infection which needs mild and damp conditions to grow. It flourishes in an air temperature of between 15 and 24°C. It can infect grass at lower temperatures if the grass is weak and the air is damp, such as during a mild winter.
In the UK, it is most often a problem in a damp spring and early summer.
Overfeeding with nitrogen (especially in autumn) can cause weak, unsustainable growth in grass. This can leave it vulnerable to pink patch infection. Sustained wet soil and low light levels which weaken grass can also contribute.
Pink patch fungal disease life cycle
Pink patch is a fungus and reproduces through releasing microscopic spores. These spores float on the wind until they land on your lawn.
Once they’ve found a suitable plant to infect they grow mycelium. These are root-like structures. They enter the grass through natural openings and cut leaves. These mycelium fibres grow between leaves and plants, spreading the infection. This is why infected areas look circular, spreading from the initial infection point.
Pink patch fungi also overwinter as a dried gelatinous mycelium. It will hibernate in the thatch of the lawn on infected dead leaves or in clipping debris. Ready to re-emerge when the conditions are correct.
It can also spread through physical transportation around and between gardens. Infected debris on a mower will spread the infection around a lawn and to other lawns. It can stick to boots and tools, ready to infect when it finds vulnerable grass plants.
If you have a weak, vulnerable grass species it is almost impossible to avoid if the infection is in your area.
Once you notice the disease it will already be in its advanced stages. The pink growths only appear once the fungus has taken hold inside the grass plants.
Does the fungus harm the grass?
Most pink patch infections only result in cosmetic damage to the grass. Most grass species will recover and grow new leaves in a few weeks once the infection has gone. This is unlike fusarium patch which can kill grass.
Severe, prolonged attacks will damage grass to an extent that the grass may die due to lack of leaf growth. But that is only in very extreme circumstances. Environmental factors often reduce the infection long before the grass dies.
Control of pink patch disease
Good selection of fungal resistant grass species will reduce infections. This means avoiding turf grass which contains fescues and keeping to modern seed varieties. Cheap grass seed often contains grass which is not disease resistant.
Also keeping the lawn as healthy as possible will reduce the chance of attack, but will never prevent it 100%. Never overfeed, or apply high nitrogen feed in the autumn or winter.
Keeping lawn thatch under control and maintain good horticultural hygiene will also help.
The best way to control an established infection is a fungicide. Modern lawn fungicides can be very expensive, but you get excellent results. Contact your local lawn care technician for advice on applying fungicides.