Wirestem

Wirestem

Rhizoctonia solani

This common soil fungus can causes several different problems for Brassica crops and different names have been given to the various stages of the same infection.

The disease is known as Damping Off when it attacks seeds and seedlings. This is most common when starting seeds indoors, but sometimes in the field too (it usually occurs when the soil is wet and there is poor air circulation). The seeds sometimes rot before they germinate, but most often the stem of the seedling turns brown around the soil line and the plant keels over and dies. The fungus may be visible on the soil surface as a gray fuzz.

If the plant germinates successfully it may succumb to the phase known as Wirestem, which shows itself as an area of constricted, dark colored infection around the soil line. This damages the outer layer of the stem, leaving the woody inner core intact (hence the name Wirestem). Unlike damping off, the stem doesn’t collapse and it isn’t necessarily fatal, however the plant won’t be as productive as it could have been.

Sometimes the fungus causes the lower leaves of infected plants to wilt or blacken and die. This kind of infection is known as Bottom Rot. Spores produced on the leaves of infected plants can spread infection to neighboring plants, so remove them immediately.

If a turnip survives long enough to produce a swollen root this may be attacked by Root Rot, whereby areas of root become sunken spongy and dark brown in color. This can happen in the ground or in storage.

The Rhizoctonia fungus that causes these ailments is present in all soils, but you can reduce the quantity of spores present by removing infected plants and keeping the beds free of Brassica plant debris. Rotate plants for 4 years. Wet soil favors the disease, so keep it well drained and have good air circulation.

Image: R.J. Reynolds Tobacco Company Slide Set, R.J. Reynolds Tobacco Company, Bugwood.org