Scientific name
Peronospora spp., Plasmopara spp. and other downy mildew oomycetes
Common Names
Downy Mildew
Downy Mildew is a destructive disease affecting ornamentals, vegetables, herbs, vines and nursery plants throughout Australia. Although often called a fungal disease, it is caused by water moulds (oomycetes). The disease thrives during cool, humid conditions with prolonged leaf wetness and poor air circulation. Early symptoms include pale yellow or light green patches on the upper leaf surface, while a grey to purple downy growth develops on the undersides of leaves. Severe infections can lead to leaf distortion, premature leaf drop, reduced vigour and significant crop losses.
Similar Diseases
- Powdery Mildew (Erysiphe spp.)
- Grey Mould (Botrytis cinerea)
- Phytophthora Blight (Phytophthora spp.)
- Leaf Spot (Cercospora spp.)
SCENARIOS AND SOLUTIONS
At the first signs of yellow leaf patches or downy growth: Apply Copper Oxychloride to help protect healthy foliage and suppress disease spread.
On ornamentals and vegetables during cool, humid weather: Apply Apparent Mancozeb 750 preventatively before prolonged periods of leaf wetness.
In nurseries with recurring Downy Mildew: Rotate Copper Oxychloride with Apparent Mancozeb 750 as part of a resistance management program.
In dense plantings with poor airflow: Remove infected foliage, improve ventilation, avoid overhead irrigation and apply a registered protectant fungicide before favourable conditions.
References
https://www.agric.wa.gov.au/plant-diseases/downy-mildew
https://www.rhs.org.uk/disease/downy-mildews
