Onion Fusarium Basal Rot

Fusarium oxysporum sp. Cepae, a fungus

Fusarium basal rot [Credit: Howard F. Schwartz, Colorado State University, Bugwood.org]

Host Plants:

On Crops: Onions

Where Found:

Mostly in warm, humid climates

Description:

Onion plants begin yellowing at the leaf tips, and gradually die back until only the neck remains. If you pull up an affected plant, many small roots will be missing, and those present may be brown and rotted or pink. Just above the roots, the base of the onion will appear corky. This disease is most common in summer when soil temperatures are above 27C (80F). Plants that have been damaged by onion root fly maggots often become infected, because the fungi can enter onion roots easily through the feeding wounds.

Damage:

As onion fusarium fungi destroy onion roots, the plants cannot make new growth. Bulbs may be small and immature. Bulb onions infected with fusarium quickly rot in storage.

Preventing Problems:

Grow onions in fertile, well-drained soil. As bulb onions gain size, taper off on watering so the soil stays somewhat dry. Once you harvest your onions, handle them gently to avoid bruising, which can invite problems with fusarium in the stored onions.

Managing Outbreaks:

Pull up affected plants and trim them for immediate consumption. Compost the trimmings in an active compost pile.

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