Manufacturers and horticultural suppliers alike have been expressing increasing interest in the development and market for plant strengtheners. A whole series of products based on substances of a natural origin, from micro-bacteria to hormones and from fungal preparations to seaweed and from algae to fatty acids, are lauded for their resilience-boosting capacities. An overview, however temporary, is presented below.

Our planet’s flora and fauna offer a wide range of substances that are beneficial to crop protection. The members of Artemis develop agents and systems that increase plant resilience to such an extent that diseases and pests simply won’t stand a chance. Artemis is the industry organisation and interest group for biological crop protection. The organisation is composed of manufacturers and suppliers of natural enemies, pollinators and plant protection products of natural origin. The substances (i.e. products) impact a wide range of functions in plant physiology.

Defence proteins

According to Alwin Scholten, cultivation advisor and owner of PlantoSys, plant strengtheners can be used in multiple ways. PlantoSys incorporates the plant-based defence protein salicylic acid into its products. Every plant produces this naturally. If the concentration is high enough, the plant starts to produce defence proteins that can block the growth of bacteria, fungi and viruses. ‘Salicylic acid is, in itself, not an antibody. It spurs the plant to produce defence proteins,’ explains Scholten. ‘However, a sufficiently high concentration must be attained in the plant before this will work. This level can be increased by administering salicylic acid to the plant’s leaves (by spraying) or roots. Stimulating the plant’s own immune system through the application of salicylic acid has proved to be highly effective in combating fungus or bacteria-related problems.’ The product appears to be highly effective against biotrophic fungi, such as powdery and downy mildew, Fusarium, rust, fruit rot (Colletotrichum) and Alternaria. It also inhibits the development of spider mites, whiteflies and aphids. Scholten recommends weekly doses as long as problems are anticipated. His product, SalicylPuur, has been approved by the Ctgb as a fertiliser. Other products developed by PlantoSys, with combinations of micro-silver and micro-copper, are marketed likewise. Scholten has noticed a growing interest among horticulturists in plant-strengthening fertilisers. ‘Four years ago the majority of the response I received was predominantly sceptical, but the sector is becoming more open-minded, particularly in the past two years.’

‘Four years ago the majority of the response I received was predominantly sceptical, but the sector is becoming more open-minded, particularly in the past two years.’

Root system

Plant strengtheners are commonly applied to the soil (the substrate) or administered as a fertiliser when watering the plant. The interest expressed by professional growers for soil and crop stimulation agents is growing, but Aly Loes Vellema of ECOstyle bv in Appelscha still has the impression that as long as chemical alternatives are still widely available, the majority prefers to stick to these. Researchers at WUR are also of the opinion that plant strengtheners are not ready to replace crop protection agents, but are a good supplement. ECOstyle focuses on ecologically responsible fertilisers, soil improvers and crop protection agents. Vellema is the supplier of the bio-stimulating soil improver Exsol P, a composite of various types of bacteria. The Bacillus combination has the capacity to free organically bound phosphates and phosphates bound to minerals from the soil, which allows the root system to develop better and the plant to better absorb water and nutrients, thus boosting overall plant resilience. ECOstyle is currently engaged in the development of plant strengthening substances, about which Vellema is not yet ready to share the details.


There are also plant strengtheners on the market that work at photosynthesis level. Pentakeep is a liquid nitrogen fertiliser that is blended with 5-aminolevulinic acid. Administration of this fertiliser causes photosynthesis to be prolonged, and as a result, the production of sugars and dry matter. Cor den Hartog of Pentagrow, importer and distributor of this originally Japanese product, has had over fifteen years of experience with the application of this product in greenhouse horticulture. Tests and studies have demonstrated that Pentakeep enhances vigour and resilience in crops. ‘Research conducted in practice has shown that crops treated with Pentakeep are less susceptible to mildew,’ den Hartog explains. ‘When applied properly, you will have a success rate of 100%.’

5-aminolevulinic acid (5-ALA) occurs naturally in plants, but its production rate depends on the speed of the plant’s metabolism. This metabolism can be accelerated by giving the plant an extra dose of Pentakeep. Plants need 5-aminolevulinic acid to produce chlorophyll. In addition to this, 5-aminolevulinic acid will increase the production of sugars and accelerate the absorption of fertilisers. The result is improved overall growth, higher production rates and stronger plants. Den Hertog confirms that Pentakeep is an NPK fertiliser and regrets that it is not yet 100% biological. The firm aims to bring a biological variant of Pentakeep to the market in the near future.

Soil resilience

On the list of the most important disciplines, Koppert Biological Systems occupies the top position with ‘resilient cultivation with NatuGro’. The international market leader of biological crop protection products has placed its resilience activities with EBIC, an international platform for enterprises engaged in the promotion of the bio-stimulants industry in an endeavour to encourage sustainable agriculture and horticulture.

Koppert is convinced that soil resilience is the key to healthy and vigorous plants.

Koppert is convinced that soil resilience is the key to healthy and vigorous plants. With a system that is composed of a diversity of products, soil analyses and expert advice, Koppert offers an all-encompassing approach under the name NatuGro. The products that are included in the NatuGro system are not stand-alone, but form part of an integrated approach: a system that enhances the biodiversity of the cultivation medium and increases the plant’s resistance to disease. A healthy and well-balanced soil life is crucial to this. Pathogenic fungi and bacteria will be inhibited because they are challenged or attacked by various groups of useful organisms in the root environment. One of Koppert’s best-known products is Trianum, a biological plant strengthener containing Trichoderma harzianum T-22 spores. While having a strengthening effect, it also enhances plant resilience in general against a variety of soil fungi. Other products included in the NatuGro system are used in the propagation stage, to stimulate root development and enhance root quality, or to improve photosynthesis.

Other multinationals such as Syngenta, BASF, Bayer and Monsanto are also manifesting themselves on the market of resilience-boosting products. Syngenta is now marketing the biostimulant Hicure and BASF has taken over Becker Underwood, specialised in biological seed treatment. Bayer has submitted an application for the approval of its ‘green’ line of Serenade fungicides and Monsanto is developing various products through its subsidiary BioDirect.

Plant strengtheners

Biobest, established in Lier and a subsidiary of Biobest NV in Belgium, has also developed activities on the market for plant strengthening products. Biobest recently expanded its product range with several items that have a plant-strengthening effect. One of these is Greenstim, about which Biobest claims that it accelerates the transport of specific nutrients. According to this supplier of horticultural products, this has a positive effect on the quality of fruit and perishability. Prestop and PreFeRal are two products that have been introduced into the Biobest range of biological products. Prestop is a biofungicide that combats Botrytis in various crops. Bart Sosef, Director of Biobest Nederland, expects the company’s range of biological products to be expanded in the near future. In relation to this, he has mentioned the fungus Trichoderma, which has a destructive effect on roots.

Biobest is evolving from a manufacturer and supplier of exclusively microbial products into a company that is also active in ‘macrobials’: useful insects and pollinators. Microbials focus more on fungicides that have a direct effect on pests, and in relation to which Sosef has mentioned the biological insecticide PreFeRal. Biobest is seeking collaboration with various partners for the further development of these products, while the marketing emphasis will be placed on guidance and advice. ‘Biobest aims to bring only products to the market that can guarantee the effectiveness they claim,’ explains Sosef.

Text: Crooijmans. Photos: Fotostudio GJ Vlekke, GAPS Photography.

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