July Pest of the Month: Powdery mildew

Powdery mildew causes disease on a large number of common nursery stock lines including many vegetable and ornamental species, e.g. tomato, cucurbit crops, rose, begonia, gerbera, zinnia, poinsettia, and many others.

Young new growth or soft, lush foliage tends to be most susceptible. Small white powdery spots occur on most host tissues including upper and lower leaves, stems and fruit.

As the infection progresses, leaf tissue dies and may fall from the plant. Growing tips may become distorted or stunted and cause plants to whither, dieback or die.

Management includes correct identification (not to be mistaken for downy mildew). Use cultural practices including growing resistant lines, adjusting nutrition to avoid succulent growth, reducing relative humidity around foliage with good ventilation and fungicides.

For more information refer to the powdery mildew factsheet and the appropriate section of the leaf spot management plan (which has a more up to date list of fungicides).

All production nurseries receive 6 free samples through the diagnostic service, Grow Help Australia, which can assist you with the correct identification of this disease.


Figure caption: Powdery mildew on zucchini leaf.