Rhizoctonia crocorum is a pathogenic fungus responsible for root diseases on many plants, particularly beet, carrot, asparagus, potato and other root vegetable crops. It is best known for causing a disease called purple root rot that many growers are unfortunately very familiar with. But what damage does this disease cause? How can you identify the symptoms? And above all, how can you biologically combat purple root rot with suitable treatments?
What is Rhizoctonia crocorum?
Rhizoctonia crocorum is a disease . This fungus is said to be saprophytic , meaning that it feeds on dead organic matter. It can survive for several years in the soil, in the form of sclerotia, resistant structures that allow it to persist in the absence of host plants.
The fungus Rhizoctonia crocorum is similar to Rhizoctonia solani, and can infect a wide variety of cultivated plants, including potatoes, alfalfa, beets, corn, brassicas, carrots and endives . Once established in a plot, it can be difficult to eradicate, due to its resilience and ability to survive in different conditions.
What are the factors favorable to its development?
The development of Rhizoctonia crocorum is favored by several environmental and agronomic conditions:
- High humidity in soils, especially in poorly drained plots.
- Relatively warm temperatures, around 20°C , are conducive to the germination of sclerotia.
- Light soils , which facilitate the proliferation of the fungus.
- The repetition of sensitive crops , such as potatoes and beets, on contaminated plots.
- A crop rotation of less than four years , allowing the fungus to persist in the soil.
- The prolonged presence of infected plant debris , which serves as a substrate for mycelium or sclerotia.
- A prolonged period between topping and harvesting , which increases the risk of tuber contamination.
These various factors increase fungal pressure and can lead to more severe infestations if preventive measures are not put in place.
Identify symptoms in vegetation
Rhizoctonia crocorum rot manifests itself in plots by localized foci, where plants show visible signs of infection.
The emergence of affected crops is often irregular or late , which indicates a slowdown in the growth of young shoots.
The fungus attack is mainly concentrated at the base of the stems , where it disrupts the circulation of sap, resulting in a general weakening of the foliage . As the infection progresses, the plants may turn yellow , losing their vigor, before wilting in the most advanced cases.
These symptoms can significantly affect production, and create areas of low yield within the plot.
Identifying symptoms on tubers
Tubers affected by Rhizoctonia crocorum show characteristic signs that allow the disease to be diagnosed. The mycelium of the fungus develops on the roots and tubers in the form of a purplish-coloured felt .
On the surface of the tubers, small black sclerotia are observed. Gradually, the mycelium penetrates the tubers and causes deep cuts and cracks in the epidermis. The flesh of the tubers then begins to deteriorate, turning into a state of grayish dry rot . Eventually, the tuber disintegrates completely, making the crop unusable.
What are the preventive control measures?
To prevent the appearance of Rhizoctonia crocorum and limit its spread in crops, several preventive measures must be put in place:
- Avoid growing susceptible plants, such as beetroot or potatoes, in plots that have already been infected.
- Practice a crop rotation of at least four years to reduce fungus pressure in the soil.
- Use healthy, certified plants to avoid introducing the pathogen into new plantations.
- Remove infected regrowth and tubers to minimize the spread of disease in the plot.
- Reduce the time between top dressing and harvesting to reduce the risk of tuber infection.
- Plant in well-prepared and amended soil , warmed and properly drained, avoiding excess humidity, conditions favorable to the development of the fungus.
- Ensure that tubers are completely dry before storage to prevent the proliferation of the fungus in the post-harvest phase.
Agrobiotop solutions against Rhizoctonia crocorum
As an expert in agrobiology, we have developed soil improvers that effectively combat Rhizoctonia crocorum:
We also recommend the following solutions to protect your plants:
