Diagnosing rhizoctonia root rot in cereals

A widespread root disease caused by a soil-borne fungus and generating yield losses of 1-5% in Western Australia each year.

What to look for

Severely stunted plants occur in patches with a distinct edge between diseased and healthy plants.
Patches vary in size from less than half a metre to several metres in diameter.
Patches of uneven growth occur from mid winter when seminal roots have established.

Affected plants are stunted with stiff, rolled leaves and are sometimes darker green than healthy plants.
Roots of affected plants are short with characteristic pinched ends: ‘spear tips’.

It is difficult to control because it can survive in the soil without a live host.
Often associated with minimum tillage systems, low soil fertility and poor plant nutrition.

Cultivation

Seed dressing fungicide

Deep cultivation before seeding can reduce the impact of rhizoctonoia root rot.
Cultivation 10 centimetres (cm) below the seed using knife-points at seeding can reduce the impact of rhizoctonoia root rot.
Levels of rhizoctonia in the soil will be highest after cereals, especially barley and lowest after canola.
Use a seed-dressing fungicide registered for Rhizoctonia suppression; these do not eliminate the patches.
Adequate fertility at seeding and tillering, especially N and Zn; N placed below seed.
Significant summer rainfall after harvest with good weed control can reduce rhizoctonia levels in the soil.