Powdery mildew diseases of poinsettia

Follow the guidance in these pages to achieve effective control of powdery mildew diseases on poinsettia crops.

Symptoms of powdery mildew diseases on poinsettia typically develop in October or November, towards the end of the production season, and after most of the cultivation inputs have been completed. Low levels of powdery mildew can render poinsettia crops unmarketable, and these outbreaks must be prevented or identified early and managed effectively to limit crop losses.

Powdery mildew has historically been found in the UK on poinsettia crops, and four pathogens are responsible. The following pages will review the fungal pathogen species that cause powdery mildew, along with the management strategies available to control these diseases. Information will be provided on:

• Disease overview
• Symptoms
• Sources and mechanisms of spread, including factors contributing to spread
• Cultural and chemical control strategies
• Fungicide resistance strategies
• Crop safety

• Liaise with your local APHA/Plant Health and Seeds Inspector if you know or suspect any powdery mildew is present on your poinsettia crop
• Inspect crops regularly for disease, especially immediately after the arrival of cuttings or young plants, and from September onwards
• Check both upper and lower leaf surfaces near the base of the canopy
• If powdery mildew occurred on the poinsettia crop in your nursery last season, consider applying a preventative systemic fungicide in September or early October, before colour development on the bracts

Understanding the biology, sources and mechanisms of spread for powdery mildew species infecting poinsettia is critical in developing effective control strategies.

Combining cultural and fungicide control measures will provide the best approach for preventing or delaying infections and treating infections when they occur. Read how to control powdery mildew diseases in poinsettia effectively.

Read the Crop Walkers' Guide: Bedding & Pot Plants for more information on powdery mildew and other common diseases of ornamental plants.

Author(s) – Dave Kaye and Erika Wedgwood, ADAS Horticulture.

Original author – Tim O’Neill, ADAS Horticulture.

Webpage content correct as of March 2021.

Powdery mildew development on the lower leaf surface

Image © ADAS Horticulture.

Close up of the powdery growth typical of powdery mildew pathogens

Image © Fera.