Phytophthora fruit disease

Phytophthora is most commonly associated with root rot disease. However, this pathogen can also damage above-ground plant parts such as fruit and leaves. The disease is known as buckeye rot in tomatoes and leather rot in strawberries.

Cause

The soil-borne oomycete Phytophthora spp.

Symptoms

Phytophthora fruit disease in tomatoes is called buckeye rot. Buckeye rot almost always develops on fruit that are in contact with infested soil. For indeterminate trellis varieties, fruit closest to the ground are at greatest risk of infection if splashed by contaminated soil.

Fruit develop a greyish-green to chocolate-brown firm rot with an indefinite, water-soaked margin and often with broad, zonate markings. The surface of the rot is generally smooth and the skin is intact. Although the rot progresses well into the flesh, affected fruit are firm initially and only soften at a late stage of infection.

How it spreads

The pathogen is a soil-inhabiting water mould and requires water for spore production and fruit infection. The disease is generally confined to wet areas where rapid disease development can occur. The spores of the pathogen move through the soil during rain or irrigation until they contact roots or splash on to fruit. Warm, wet weather favours infection and disease development.

The pathogen can also survive on rotting fruit and stems where sporangia are produced in the presence of water. Wind-blown rain and water splash carry the sporangia to plants where they infect fruit and stems through either wounds or undamaged tissue. The pathogens can also spread rapidly in surface water and in soil stuck to machinery and animals.

Crops affected

Tomato, strawberry, onion, fig, durian and papaya.

Control

Avoid planting in infested areas, particularly low-lying areas of fields.

• Choose well-drained sites and plant susceptible crops on mounds. Remove and destroy all fallen fruit and infected plants.
• Avoid introducing the pathogens into clean areas.
• Apply recommended fungicides during wet weather in very susceptible crops such as papaya.

Chemical registrations and permits

Check the Australian Pesticides and Veterinary Medicines Authority database for chemicals registered or approved under permit to treat this pest on the target crop in your location. Always read the label and observe withholding periods.