July Pest of the Month: Algal leaf spot

Name: Agal leaf spot (cephaleuros virescens)

Symptoms are mainly found on leaves but depending on the plant species it can infest twigs, limbs and fruit. The disease usually attack the leaves on low hanging branches without affecting higher foliage. Symptoms include green, yellow-green, or rust coloured leaf spots up to 5mm in size, which appear raised, roughly circular and cushion like.

Stems many develop cankers where infestation is high, and may be covered with reddish brown hairlike fruiting bodies and eventually produced rust-coloured “spores”. Fruit damage is limited to the skin with slightly sunken, cracked dark appearance.

Severe infestations can lead to stunting, loss of plant vigour and reduced yield in citrus fruit.

Transmission:

Algal lead spot is a plant-parasitic algae known to cause disease in wet weather. It produces spores that are spread by wind, water splash, carried on insects e.g. fungus gnat, or on staff, equipment and tools.

Favoured by:

Favoured by warm, humid conditions with limited air flow, environments that remain wet for long periods, crowded plant spacing and free standing water in greenhouse production. The alga commences colonization late in the summer and progresses through the winter months.

Host range:

Usually found on plants with leathery leaves such as camellia, acacia, albizzia, avocado, bischofia, bixa, carambola, camphor-tree, cinnamon, cotoneasters, grevillea, guava, hollies, jasmine, jujube, loguat, magnolia, pecan, Japanese persimmon, privet, rhododendrons and viburnums, as well as some palms e.g. fish-tail and Queen.

For further information please refer to the Pest ID Tool at: https://pestid.com.au/disease/algal-leaf-spot-algal-spot-red-leaf-spot-green-scurf

Note that the Pest ID tool 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).