Wilt

Fusarium and Verticillium wilts are caused by soil-dwelling fungi that infect plants through the roots and colonise the water-conducting (vascular) tissue in the stem. As the fungus spreads internally, it clogs these tissues and produces toxins, restricting water movement to the leaves. This is different from a leaf-spot or rot disease, as most of the damage happens inside the plant and isn't visible until the vascular tissue is cut open.

On the plant itself, the fungi are microscopic and not visible to the naked eye, but their effect is distinctive. If you slice open a wilting stem near the base, the internal tissue often shows brown or reddish-brown streaking running lengthwise, in contrast to healthy white or pale green tissue. In humid conditions, Fusarium can sometimes produce a faint pinkish or salmon-coloured fungal growth at the stem base or on dying tissue, while Verticillium tends to show darker grey-brown staining. Both fungi persist in soil for years as tiny resting structures, surviving between susceptible crops.

These wilts affect a wide range of vegetables, ornamentals, and some turf and tree species across Australia, and are more common in warmer months and in soils that have grown susceptible crops repeatedly. Fusarium wilt tends to favour warmer soil temperatures, while Verticillium wilt is often more active in cooler soil. Both are worsened by plant stress, root damage, and poor drainage.

Management relies heavily on prevention rather than cure, since there is no way to treat the vascular infection once established. This includes choosing resistant or tolerant varieties where available, practising crop rotation to reduce soil-borne fungal load, avoiding waterlogged or compacted soil, minimising root damage during cultivation, and removing and destroying infected plant material rather than composting it. Improving soil health and drainage, and disinfecting tools between plants, also helps reduce spread.