April Pest of the Month: Anthracnose – Colletotrichum spp

Anthracnose is a common nursery pathogen causing leaf spots and small water-soaked circular lesions on leaves, stems or fruit. With time, spots enlarge and become tan to dark brown or black in colour. Sometimes leaf spots may be surrounded by a bright yellow halo. Lesions may become sunken and produce concentric bands of tiny black fruiting bodies on the dead tissue in the centre of spots. Salmon-coloured spore masses may exude from fruiting bodies under conditions of high humidity. Symptoms caused by anthracnose tend to be very similar to those caused by a range of other symptoms.

Spores are spread by water splash from rain and overhead irrigation. The fungi may survive on undecomposed plant residues in the growing area or on numerous alternative crop and weed hosts. Spores spread rapidly during wet, humid windy weather, including water splash from overhead irrigation. Anthracnose tends to be more severe during warm, humid, wet conditions and can infect a very wide range of plant species.

Once damage has occurred it will never recover. Therefore, proactive management is recommended and includes:

  • Decrease periods of leaf wetness, particularly during high risk times
  • Increase ventilation
  • Grow Plants under optimal conditions as thriving, healthy plants can resist disease relatively well.
  • Do not over fertilise
  • Clean and disinfest growing areas between crop cycles
  • Grow resistant/tolerant varieties
  • Propagate only from healthy mother stock
  • Avoid introducing diseased plants

For further information on the management of Anthracnose in production nurseries refer to the factsheet and leaf spot management plan. For photos of a range of plants infected with Colletotrichum refer to the Pest ID tool.

If you suspect your stock is suffering from a leaf spot pathogen it is recommended to submit plants for diagnostic testing at one of the many services around Australia. In addition, all production nurseries receive 6 free samples with Grow Help through a nursery levy, Hort innovation and Queensland Government funded project.

Figure Caption: Anthracnose leaf spots and blight on Pothos.