Contaminated seed a common source of anthracnose

Anthracnose – Colletotrichum spp. is the pest of the month at Your Levy at Work. Below is some information about this common nursery pathogen.

Symptoms
Symptoms vary with host, but spots often initially appear as 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.

Transmission
Sowing contaminated seed is the most common means of introducing the pathogen. Spores are spread by water splash from rain and overhead irrigation. The fungi may survive on undecomposed plant residues in the soil or on numerous alternative crop and weed hosts. Spores spread rapidly during wet, humid windy weather.

Favoured by
These pathogens favour warm, humid, wet conditions. The pathogen can survive on the leaf surface until conditions are favourable for infection and disease development through stomata or wound. As free moisture is required for infection, avoid wet foliage, particularly during warm weather. Plants can be very susceptible during mist propagation.

Host range
This fungi is found on a very wide range of hosts including azalea, cyclamen, orchid, pansy, palms, snapdragon, violet, zinnia, protea, rose, ivy, croton, Dieffenbachia, Cordyline, Dracaena, Ficus, and food crops such as rockmelon, cucumber, strawberry, capsicum, papaya, avocado. It is also found on weed species such as Noogoora burr (Xanthium pungens) and Bathurst burr (Xanthium spinosum).

Source: Your Levy at Work

Publication date: Thu 9 Nov 2017