Anthracnose is caused by the fungus Colletotrichum graminicola. It can attack most species of grass, but annual meadow grass (Poa annua) is very susceptible (the previous name of this disease was ‘Basal rot of Poa annua’ (Annual meadow grass)). Creeping bent grass is also susceptible to attack and to a lesser extent fescue.
Antracnose is a stress disease, attacking grasses that are suffering due to environmental factors, mechanical and turf management practices. Heavy wear, causing compaction, close mowing, lack of nutrition and an excessive thatch layer can play a major influence on the cause.
The bacteria causes two types of disease, depending on climatic conditions, one is a ‘foliar blight’, the other a ‘basal rot’.
Identification of Anthracnose
Anthracnose usually appears on the lawn during the late summer and can persist deep into winter months, even into the following spring. Be vigilant and look for annual meadow grass plants that are starting to turn yellow, with the youngest leaf turning an orange to red colour on infected plants.
Foliar blight is often mistaken as drought affected turf, as it is most common during hot dry spells in the summer months. The grass initially turns yellow before turning a tan colour as it forms irregular patches of infected turf.
Basal rot occurs with the grass plants turning yellow during late summer, with the youngest leaf turning an orange to red colour on infected plants.
As the severity of this disease increases, the infected patches can grow to 150mm in diameter and the base of the infected area turns black and the grass can easily be plucked from the base of the turf.
Every effort should be made to control this disease at an early age, such is the damage it can cause if it is left unchecked.
Causes of Anthracnose
As we previously mentioned anthracnose is a stress disease so pay attention to keeping the lawn in a healthy condition with good lawn care practices. These include:
- Ensure the lawn receives adequate nutrition, (however it is important not to over apply nitrogen during the late summer and autumn as it may lead to problems with fusarium patch disease).
- Soil compaction caused by excessive traffic can also influence anthracnose.
- Prolonged leaf wetness will encourage the spread of this disease.
- Hot and dry conditions leading to drought stress, will encourage anthracnose.
How to prevent and control Anthracnose
Focus on prevention by remedying the causes of anthracnose:
- Ensure the lawn receives adequate nutrition to keep the grass in healthy condition.
- Relieve compaction with aeration, in the form of slitting, spiking or even hollowtining. If possible reduce the amount of traffic the lawn receives.
- Reduce the thatch layer to an acceptable level.
- As anthracnose predominantly attacks annual meadow grass, reduce the amount of this grass in the lawn by encouraging disease resistant grasses with good lawn care management practices.
- Raising the height of cut on the mower will also help reduce the stress levels of the grass and help combat the spread of anthracnose.
- Reduce the time that the leaf surface remains wet by removing early morning dews.
- Prune back tree branches and any excess vegetation, to reduce shade and to promote air movement, allowing the grass to dry quicker.
Fungicides are only available to turf professionals who have the relevant spray certificate to apply chemicals to turf. However, once this disease has become established, even with chemical control, success will be very limited at best.