June Pest of the Month: Grey mould

Grey mould has a distinctive appearance that can potentially be identified with a microscope or even a good hand lens. It can grow on dead and decaying tissue and may cause a variety of symptoms including leaf and flower blights, spots, blotches, wilts, cankers, rots, damping off and storage diseases.

Usually softer tissues such as petals are blighted, though leaf spotting, stem blights and rotting of cuttings and seed occur, especially in crowded situations. Tissue infected with grey mould tends to have masses of grey fungal growth including masses of spores.
Spores are spread by wind, water splash, insects such as bees and aphids and handling of infected material. Spores can also be carried on seed, cuttings, seedlings and bulbs. The spores need moisture for germination and infection.

They are favoured by cool, wet weather conditions when temperatures are below 25oC (optimum temperatures are 18o – 23oC). Closed growing areas where humidity is high suit Botrytis infections. Autumn and spring overcast days and shorter day lengths are also favoured. Grey mould can infect a very wide range of plant species. Some species (such as lisianthus and cyclamen) are extremely susceptible. Other hosts include viola, strawberry, pelargonium, blueberry, daisies, Corymbia spp., lavender, impatiens, rose, Cordyline, poinsettia, Dianella, Dietes and many others.

If you suspect you are experiencing disease caused by this fungus, consider sending a sample for diagnostic testing. Initial results are often very fast owing to their distinctive spores that almost always occur on infected tissue. All production nurseries receive 6 free samples through at Grow Help Australia funded by Hort Innovation, the nursery levy and Queensland Dept of Agriculture and Fisheries.

For more information on grey mould refer to the factsheet and the leaf spot management plan, which has information on fungicides available. You may also find the fungicide and resistance management factsheet helpful. Additional photos on symptoms produced by grey mould can be found at the Pest ID tool.

Close up of grey mould (Botrytis)