Substrate concept to combat sciarid infestation

Interview with Eckhard Schlüter about major progress in the organic substrate sector

Eckhard Schlüter works at the Klasmann-Deilmann Advisory Services & Quality Management department and is concerned primarily with the organic substrate segment. In the following interview he describes a substrate and fertiliser concept for organic substrates that has been developed in collaboration with Osnabrück University of Applied Sciences and which can reduce pressure from sciarid flies by up to 80 per cent.

Question: Eckhard, where do sciarids occur and what are the consequences?

Eckhard Schlüter: Sciarids are very common and greenhouses provide ideal living conditions for a few of the 1800 species that there are altogether. They infest the growing media of ornamentals and crops or live on the algae or moss coverings that form in moist areas. The larvae can damage the plant roots. Although the sciarids are harmless for the plants themselves, they are regarded as contamination in the trade so that retailers may refuse to accept such plants. Sciarids are one of the central plant protection problems in the production of organic herbs and horticultural businesses are faced with high costs for the biological control of sciarids.

Question: How come the infestation rates are especially high in the organic sector?

Eckhard Schlüter: We have just discovered that this is due in particular to the special recipes used for organic substrates. They currently contain a minimum of 30 per cent of alternative raw materials, such as compost, wood fibre or coir, as well as solid organic fertilisers. This is in response to demand from organic associations to replace peat to as great an extent as possible. However, this mixture unfortunately offers ideal living conditions for sciarid larvae. There are several reasons for this: firstly, these substrate blends obviously emit substances that attract sciarids and secondly, they provide an excellent and direct source of food for the larvae.

Question: What are these substances that provide food for the sciarids?

Eckhard Schlüter: We conducted lab trials to examine all these components systematically. Our tests revealed that substrate components obtained from composting processes pose a particular challenge if they are not properly decomposed and still contain a high share of easily degradable organic matter. It was also clear that the organic fertilisers used in these products obviously play an even more important role. Depending on their composition and structure, they provide a direct source of food for the larvae. However, the tests also showed that our GreenFibre wood fibres and the coir products we use are not readily accessible sources of food.

Question: What conclusions have you drawn from the tests?

Eckhard Schlüter: As a consequence of the test findings, we are changing the substrate constituents we use to deprive the larvae of their natural food source. What this actually means in practice is that we now use only perfectly rotted, mature green compost from our own composting plant. This green compost is marketed under the TerrAktiv brand and is highly appreciated in the organic horticultural business. As far as the organic fertilisers are concerned, our tests revealed that virtually all commercially available solid fertilisers are unsuitable.

We have therefore developed an innovative gel-based fertiliser formulation in cooperation with a well-known Dutch fertiliser producer. The fertiliser is finely distributed throughout the growing medium and its special encapsulation makes it difficult for the sciarid larvae to access. In the course of the development process, our technical department also designed a special dosing system for the substrate mixing plant which enables micro-fine distribution of the fertiliser.

Question: What is so special about this concept?

Eckhard Schlüter: There are actually two special features: firstly, the idea that different modules can be combined in any given substrate to match the individual needs of the company concerned. These modules are white peat, coco, wood fibre and – a very important aspect – we can still continue to work with a share of valuable green compost in organic substrates. TerrAktiv green compost invigorates the substrate, suppresses pathogens and promotes the mineralisation of organic fertilisers.

The second thing is our new fertiliser formulation, which consists of fermented vegetable or hydrolysed animal components. These fertilisers are highly efficient in providing nutrients and are also rich in amino acids, which help to strengthen the plants. They cannot be used directly by sciarid larvae and therefore enable horticultural businesses to use organic substrates with a significantly higher level of basic fertilisation again.

Question: And this substrate concept stands for genuine progress?

Eckhard Schlüter: Yes, we have been using this concept with an increasing number of customers for some years and the results are very positive. Thanks to the experience we have acquired to date, we are now in a position to offer a customised fertilisation concept for each grower.

In response to increasing demand from Benelux and France, we are currently also installing a fertiliser dosing system for organic substrates at our production plant in the Netherlands.

Question: Who will benefit from this substrate concept?

Eckhard Schlüter: It is primarily suitable for horticultural companies looking for organic herb growing media with a low to medium level of basic fertilisation which they can combine with their own later liquid fertilisation strategy. This combination is currently the most efficient way to control pressure from sciarids.

However, it has also shown other promising potential uses in growing media for sensitive young vegetable plants. The fertiliser is released at a careful rate and we also noticed that the free amino acids yielded stronger plants.

Eckhard, thank you for taking the time to talk to us.