Basil Downy Mildew

(Peronospora belbahrii)

Basil Downy Mildew is a relatively new disease in Australia, it is a significant disease which eventually kills infected plants. The pathogen which is a type of fungal disease has the potential to be an important disease, severely affecting certain species of Basil, especially Sweet Basil.

The disease first appears on the undersides of the plants leaves as greyish dark colored mould, with visible spores, these are the fruiting bodies of the fungus. The mould will quickly spread over the rest of the plant and onto nearby plants.  Affected leaves will start to show signs of yellowing on the surface of the leaf, spreading to other leaves eventually killing the leaves and plant.

Basil Downy Mildew is spread quickly and easily, with spores being carried in the wind and these spores can be carried long distances making quarantine attempts difficult. The disease is present in all parts of infected plants. It prefers warm, humid moist conditions.

Plants showing signs of Downy Mildew should be removed and destroyed ensuring the fungus does not infect other plants if possible. Fungicides have had little affect at controlling the disease. Growing plants in well ventilated open areas which receive plenty of sunshine may help reduce plants becoming infected. To date plant breeders have not been able to breed a resistant variety of basil.  

There is some good news though, some species of basil are showing signs of resistance, namely the red leaf varieties, Thai and Lemon species of basil. These are options for those wanting to grow this wonderful herb.   


Learn more about Pests and Diseases with our 100 hour course Horticulture III (Plant Health).