July Pest of the Month: Phoma blight

Name: Phoma blight, Phoma spp.

Species of Phoma can infect a wide range of vegetable and ornamental crops including conifers, Clematis, Vinca minor, chrysanthemum, sunflower, ash, cedar, fennel, coriander, aloe vera, citrus, papaya, mango, coffee, onion, crucifers, celery, beets, tomato, grevillea and capsicum.

Symptoms: 

A variety of symptoms can be produced depending on host and pathogen species.  Phoma species can cause chlorosis and necrosis of foliage, tip dieback, defoliation and seedling damping off.  In some hosts, the pathogen can also cause stem blight and cankers, as well as root rot, crown rot and fruit rot.  The pathogen produces fruiting bodies (pycnidia) on dead tissue, which exude spores in a sticky matrix.

Transmission:

Spores of the fungus, which may either be present in the soil or on infected plant material, are commonly spread by water splash (overhead irrigation or rain splash).  This may result in a build-up of spores around the stems of young seedlings, causing a crown rot which then spreads up through the stems and leaves of infected seedlings.  The fungus can also infect older seedlings and plants, causing leaf spots, stem blight and root rot.  Infection can either be through wounds or by direct penetration of host tissue.

Favoured by:

Disease development is favoured by wet and humid conditions.  Depending on the host and pathogen species, optimum temperature requirements for disease development varies from cool to warm conditions.

For further information refer to the factsheet on fungal leaf spots and latent fungal pathogens nursery paper. Or alternatively refer to the industry Pest ID Tool at https://pestid.com.au/disease/phoma-blight.

Note that the Pest ID tool which covers a wide range of significant industry pests and diseases  is now available with free access to industry.

An initiative of the Nursery Levy funded National Nursery Industry Biosecurity Program (NY15004) and ‘Building the resilience and on-farm biosecurity capacity of the Australian production nursery industry’ Project (NY15002).