Fusarium rot

Cause

The fungi Fusarium spp.

Symptoms

Potato
This is a dry, sunken rot, often giving potato tubers a wrinkled appearance. Pockets within the rot generally fill with white or pink wefts of the fungus that may sometimes be present on the outer surface. If the rot starts around the point of attachment, it is known as 'stem end rot' and may indicate the presence of Fusarium wilt in the parent crop. Other fungi can also cause stem end rot.

Melons
In rockmelons, symptoms usually occur at the stem end and begin as small scattered spots on the skin. Affected tissue tends to be spongy or corky and, as the disease progresses, becomes covered with a white or pinkish mould. There is usually a distinct margin between healthy and affected skin.

Sweet corn
A white fungal growth develops, covering individual kernels scattered throughout the ear.

How does it spread?

The fungi are common soil inhabitants that enter the tuber through wounds. Because the rot develops slowly, it is generally visible only after potatoes have been stored for some time. Relatively high storage temperatures favour the development of Fusarium rots. Planting affected seed usually results in a poor stand.

Melons are usually infected on the underside however spores may splash on to any part of the fruit during rain or irrigation. Some form of wound is necessary for infection. Hot, wet weather, particularly during harvest, favours rapid breakdown of fruit.

Air-borne spores infect silks of sweet corn and the pathogen grows down the silks as they start to die, eventually colonising the kernel. Infection usually occurs following cob injury, including insect feeding. Generally associated with high temperatures and moisture stress.

Crops affected

Potato, rockmelon and sweet corn.

Control options
  • Inspect seed consignments on arrival and reject those affected.
  • Store the consignments in cool, well-ventilated conditions.
  • Reject affected tubers before cutting.
  • Apply the recommended fungicides before storing.
  • Avoid injury to fruit skins by not harvesting under very cold or very dry conditions.
  • Optimise grading equipment and grading speed to minimise damage to tuber skins.
  • After harvest or grading, allow a curing period (above 12ºC with good ventilation for at least one week) before placing tubers in a cool store.

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