P&PDL Picture of the Week for
August 31, 2009

Fusarium Wilt and Stem Rot of Chrysanthemum

Tom Creswell, P&PDL Director, Purdue University

As cooler weather approaches a bright spot in the otherwise fading landscape is the Chrysanthemum. Chrysanthemum producers sometimes run into a troublesome disease known as fusarium wilt and stem rot.  The fungus (Fusarium oxysporum) invades the plants through the roots, eventually entering the water conducting vessels of the plant and plugging them so the plant can no longer take up water. Early symptoms include yellowing and wilt. When stems are split they show red to tan discoloration inside and eventually the stem outside shows white tufts of spores.

It is common to see one dead plant in a multi-plant pot or to see a single branch wilting and showing leaf death. Eventually the entire plant dies as the infection spreads. The fungus can be spread on contaminated pots, tools and anything that moves growing media. It also produces spores that are resistant to drying and cold and can survive long periods in soil or plant debris, so cleaning up greenhouse and outdoor mum growing areas is critical to preventing a repeat of the same problem in the next crop. Fungicide treatments have to start early (soon after transplant) to be effective.

The disease is not often a problem in the home landscape because infected mums usually show symptoms and are discarded before they reach retail stores.

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Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service