Control of Rhizoctonia solani in potato cultivation (2016 - 2020)

Initial situation and need

The fungal pathogen Rhizoctonia solani causes root rot disease on potatoes with a variety of symptoms throughout the growing season. Typical symptoms are sclerotia (pock-like permanent stages) on the tuber surface. Infected tubers are a central element for the further spread of the fungus. From there, the entire root area of the plant is infected; this leads to uneven emergence of the potatoes, the erosion of the main and secondary roots, deformed tubers, and, later in the course of disease development, to the dry-core symptom (dry rot). With the death of the haulm, the black sclerotia form again on the daughter tubers. The fungus can also survive on crop residues and poorly decomposed organic matter in the soil. Healthy plant material therefore represents a glaringly important component of preventive plant protection in organic farming. Since there are no direct control options for the pathogen in organic farming, keeping the soil and planting and harvesting material healthy is an essential contribution to the economic success of operations on potato farms. The decisive solution for the operational group resulted from results of previous research work at the University of Kassel. It was shown that the use of composts as a row application to potatoes is a promising way to control soil-borne plant pathogens. Composts (biomass/green manure composts) with a correspondingly high quality possess the property for suppressive effects, i.e. due to their high microbial activity the composts are able to control the pathogen.

Concrete task and project objectives

Agricultural companies from Hesse, compost plant operators, advisors from organic associations, an industrial company and researchers from the Universities of Kassel and Göttingen came together to form the OG Rhizofrei with the aim of developing a technical solution for combining potato planting methods and row application of compost as an innovation for the control of R. solani in organic potato production.

Implementation and results

During the project, the functionality of the process was documented and established.

• The production of the composts (biosolids/green manure composts) was designed and verified at model and practical levels. The processes are set up in such a way that they can be carried out under practical conditions on composting plants with only a few exceptions. Material selection, rotting times as well as temperature and moisture conditions have to be observed to ensure the positive microbial conditions.
• The monitoring of the compost effects by means of field and demonstration trials showed predominantly positive results in the reduction of sclerotia in the harvested material; the proportion of tubers with a sclerotia content < 1% of the tuber surface was clearly increased. This resulted in a 10-15 percent increase in marketable yield and thus interesting economic advantages when the process was applied.
• The optimization of the compost application technology consisted in the production of a prototype with a scraper floor bunker for the compost as well as appropriate application aggregates, which allow a uniform transverse and longitudinal distribution of the compost. An even placement of the composts in the row can thus be ensured.
• The optimization of the compost application technology consisted in the production of a prototype with a scraper floor bunker for the compost as well as corresponding application aggregates, which allow an even transverse and longitudinal distribution of the compost. An even placement of the composts in the row can thus be ensured.
• The demonstration of the overall process took place at the Eco-Field Days 2017 and 2019, as well as with a technical information film.

Recommendations for practice

What is relevant to practice and feasible?

The project was able to solve the questions that are very relevant for practice. This concerns the technology, the compost production and thus the connection to compost management and the effects of the composts. The predominantly positive effect on the tuber health of the crop could be confirmed, as in the previous projects. However, it should be noted: overall, it is a biological system that is always influenced by the general conditions. In addition, the misunderstanding that bad potato planting material can become good planting material should be prevented! Composts can lead to many positive effects, but they cannot work miracles.

Has a practical solution been found for the machine? Where can the machine be obtained?

The machine is a practical solution, but it is a prototype. As of Sept 2021, the company Heiss ALL-IN-ONE is working on a series development.

Can composts be purchased? What are the requirements?

Although compost production for application against a soil-borne plant pathogen is possible on the conventional compost plants, it is warned against buying the composts "off the shelf". It is imperative that expert advice be sought.

How do I find out where to buy composts?

Consultation of the cultivation association, Fibl company list for organic farming according to the listed compost plants in the region.

What qualities must the composts have?

All green waste and organic composts must comply with the guidelines of the Bundesgütegemeinschaft Kompost (RAL GZ 251) for organic farming. Batch analyses are mandatory for quality criteria. Stricter criteria for foreign matter content, heavy metals and hygiene for Naturland and Bioland must be observed. Before spreading green waste and biogut composts, this must be approved by the associations. What are the application rates and what confection must the composts have? 5-6.5 tons of dry matter per hectare per year as a row application. Dry matter content of 60-70% with 10 mm screening.

Success factors and tips for new groups

Choose manageable group sizes for OGs and limit to a maximum of three main objectives; rule of thumb: the more complex the issue the smaller the group. Allow plenty of time for communication with each other and for outreach. Share experiences in workshops.