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Fusarium wilt

Also known as Fusarium oxysporum, Panama disease (in bananas)

DiseaseHarmful
Brown discoloured vascular tissue in a sweet potato stem with Fusarium wilt Photo: Clemson University - USDA Cooperative Extension Slide Series · CC BY 3.0

In short

Fusarium wilt is a soil-borne fungal disease caused by forms of Fusarium oxysporum that enter through the roots and block the plant's water-conducting tissue. Each form attacks only a particular host group. There is no cure once a plant is infected, so prevention and resistant varieties are the main tools.

How it looks

The fungus itself is not visible outside the plant. The key sign is inside: peel back the outer layer of the lower stem or cut across it and the water-conducting tissue (xylem) is stained brown, often all the way from the shoot tips to the soil line. Outwardly, older, lower leaves droop and yellow first.

Signs

Drooping of older lower leaves, yellowing and browning of foliage, stunting and eventually death of the plant. Some hosts show vein clearing on younger leaves early on.

Life cycle

The fungus enters through small roots, moves up the xylem and blocks water flow. It survives for many years in soil and plant debris as thick-walled resting spores (chlamydospores). It is spread with infested soil, potting mix, water and infected plants or planting stock.

What favours it

Warm temperatures favour the fungus and its spread. Poor drainage and overwatering are also listed as factors to avoid.

Prevention

  • Grow resistant cultivars where they exist.
  • Use clean, fresh potting mix and clean pots; do not move soil from infested beds.
  • Improve drainage and avoid overwatering.
  • Do not replant the same host group where the disease has occurred; plant a different genus instead.

Treatment

Start with the first step and move down only if the problem persists.

  1. There is no effective fungicide or cure for infected plants.
  2. Remove and dispose of infected plants, including roots, promptly; do not compost them.
  3. Discard the potting mix from infected pots and clean the pots before reuse.

Pros and cons

Cons

  • Incurable once a plant is infected.
  • Resting spores persist in soil for many years.

Look-alikes

Root rot
Root rot leaves roots brown and mushy; fusarium wilt stains the internal vascular tissue of the stem.
Underwatering
A dry plant recovers fully after watering; fusarium wilt progresses despite moist soil.
Southern blight
Southern blight rots the stem at soil level and shows white fungal threads and mustard-seed-like sclerotia.

Affected plants

Tomatoes, beans and other legumes, cucurbits, sweet potatoes, bananas (Panama disease), cotton, date palms, carnations, chrysanthemums, asters, some cacti, hebe and pyracantha, among others; each forma specialis attacks only its own host group.

Sources

  1. Fusarium Wilt (Home and Landscape) — UC IPM
  2. Fusarium wilt — University of Minnesota Extension

Written in our own words from these sources. Check a product label before using any treatment.