Rhizoctonia root rot disease is caused by the soil fungus Rhizoctonia solani. In sugarbeet, this disease causes a dark brown rot to develop from the root to the crown of the sugarbeet.
Spreading
In the field, the development of the fungus is favored by the presence of host plants, abundant rainfall and high spring and summer temperatures. Poor soil structure also promotes its proliferation.
The strain of Rhizoctonia solani, which is responsible for Rhizoctonia root rot in sugarbeets, has a relatively broad range of hosts: it can attack other crops (corn, vegetables, etc.), rye grass and some adventitious plants. The sugarbeet-growing areas most severely affected by the disease are often areas where corn is also grown.
Symptoms
The disease becomes apparent in late summer or early autumn. The damage appears in the form of small patches on the sugarbeet leaves that grow gradually. Wilting is observed in the foliage, which develops until the leaves perish although they remain attached to the sugarbeet crown. The dead leafs form a brown rosette of which new leaves appear in the middle. A brown or black dry rot can be observed on the surface and/or inside of the root and crown.
The disease is found in many regions of the world and in all types of soil. In highly infested plots, the damage can have major economic consequences: major loss of yield, reduction in sugar content, increase in soil tare, poor industrial quality and storage difficulties.
Control
No fungicide is currently approved in Europe that controls Rhizoctonia root rot effectively. In the event that a major infestation is expected the following year, growers are advised to combat the disease by:
1. Adopting appropriate agronomic measures
- Extending rotation: ideally, 3 to 5 years should be left between two successive beet crops in the same field
- Avoiding crops that act as host to the fungus during rotation and careful weeding
- Maintaining a good soil structure (in particular by avoiding soil compaction)
- Avoiding the storage of diseased sugar beet as far as possible
2. Using a variety of seed with dual tolerance Rhizomania and Rhizoctonia root rot SESVanderHave is currently leading the market in dual Rhizomania-Rhizoctonia root rot tolerant varieties. The varieties with dual tolerance currently sold by SESVanderHave in France, Belgium and the Netherlands combine a very high degree of resistance to the disease and excellent performance in terms of financial return, root yield and sugar content.
