July pest of the month: Phytophthora

2 July 2024

Widespread in production nurseries across Australia, Phytophthora is a group of dangerous pathogens containing harmful microorganisms that cause severe root rot and plant death.

Phytophthora often occurs when irrigation water is not disinfected and when water is recycled.

It is crucial to implement preventative measures to protect crops because once a plant is infected, it cannot be cured.

Selling infected plants spreads the disease.

Symptoms

Phytophthora can cause damping-off of young plants. The infection typically starts at the root tip, rapidly spreading to all below-ground parts, causing the plants to fall over.

In mature plants, symptoms include appearing water-stressed, chlorotic (yellow), stunted and wilted despite regular watering.

Management and prevention

The key to managing Phytophthora is prevention. To effectively stop the spread of this disease, follow these steps:

• source plants wisely – purchase plants from nurseries that adhere to best management practices
• manage water – disinfect irrigation water or use clean water sources such as town water
• control growing conditions – grow plants off the ground, ideally on benches, avoid overirrigation and maintain optimal growing conditions.

For more information on the biology and management of Phytophthora pathogens see the soil borne disease:

• management plan
• factsheet
• webinar.

You can also check out the Pest ID tool.

If you think your plants may have a root disease, we recommend you submit a sample to a diagnostic laboratory for identification. All production nurseries receive six diagnostic samples at Grow Help each year until the end of 2025.