Anthracnose is caused by the fungus Colletotrichium graminicola. Although Anthracnose can affect other grasses, it is particulary damaging to closely mown Wintergrass (Poa annua). Colletotrichium graminicola is capable of surviving from season to season as a saprophyte in dead plant tissue in the thatch and on stems beneath the leaf sheath. It can also reside in the sheaths of grass plants. Once temperature and moisture reach favourable levels a new infection begins. Anthracnose is transported place to place via grass clippings.
Anthracnose produces a characteristic fruting body called acervuli in warm weather. These black fuiting bodies, which possess black spines that protrude from them, can be observed with a hand lens or stereo microcope. Anthracnose can be found in the roots, stolons and leaves, but it is most commonly found on the foliage of the grass plant.
Anthracnose is usually seen between mid to late summer to late Autumn. Anthracnose is characterised by irregularly shaped pacthes of yellow-orange turf, ranging in size from a few centimetres to a metre. Leaf lesions usually appear as elongated reddish brown spots on the leaves. These spots will enlarge, eventually encompassing the entire leaf blade. Acervuli can be seen on the foliage as the disease progresses, growing outward throgh the surface of the blade. Acervuli are particularly apparent on dead leaf tissue destroyed by the disease. In cooler, wet conditions, Anthracnose may cause a distinct rotting at the base of the plant.
Anthracnose is considered to be a 'biological indicator'. If the disease is present, turf growing conditions are likely to be poor. The disease is favoured by compaction. Low fertility and prolonged soil wetness also favour disease development. Results of laboratory studies show that the optimum temperature range for growth of the fungus is 22-31 degrees celcius. Inoculation studies show that Colletotrichium graminicola can cause disease on Wintergrass between 27 - 33 degrees celcius. Prolonged leaf wetness has also been proven to be important in the development of the disease.
Cultural Control Practices
Anthracnose can be managed with light nitrogen applications (0.25kg elemental N per 100Sq.m every 3 weeks - Vargas, 1994) when it occurs during cool weather.
Compaction should be avoided. This can be undertaken by moving the pin position regularly. Regular aeration or vertidraining is also beneficial.
Chemical Control Options
Anthracnose can be managed with systemic fungicides applied every 2-3 weeks, or with contact fungicides applied every 7-10 days. Chemical control options are highlighted below;
Azoxystrobin – eg. Heritage Maxx.
Tebuconazole / Trifloxystrobin – eg. Dedicate.
Propiconazole – eg. Banner Maxx.
Azoxystrobin / Propiconazole – eg. Headway Maxx.
Chlorothalonil / Fludioxynil / Propiconazole – eg. Instrata.