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The Role of Biostimulants in IPM

26 April 2021

The overriding principle of IPM is to manage the health of a crop holistically, rather than just to focus on individual pests and disease and then deal with them with single tools in isolation. We are used to the concept that we might try and combine interventions like rotation, tillage, varietal resistance with targeted pesticides to reduce pest and disease pressure, but the concept of trying to work with and stimulate the plants own natural processes using biostimulants is newer and less well understood. Even the definition of what a biostimulants is often hazy. They should not be primarily nutritional / fertiliser products nor should they claim direct efficacy against pests or diseases or they would be dealt with under plant protection product regulations. Strictly,  biostimulants are products that promote or augment natural processes within the plant. So they might for example help to make the uptake of available nutrients more efficient or they might make plants more resistant or resilient to external stresses by reducing water loss.

Without doubt there are examples of biostimulants which can help enhance crop yield and /or reduce the risk of crop losses and reduce our reliance on artificial inputs, however it is an exceptional broad area and there also some fairly costly and highly variable examples where evidence of proven benefits to the bottom line profits in a crop are sparse.   Even the very term causes confusion. It covers a huge range of product types ranging from inorganic salts right through to examples comprising microbes and nematodes. Even the term ‘bio’ could infer they are somehow natural and biologically generated but while this will be true for some (such as seaweed extracts) it is manifestly not so for some of the inorganic salts. And some may be derived from natural sources but, where these are animal based, they may not be acceptable to end markets or users. For example amino acids derived from beef or pork sources.  They are not pesticides which would have to go through more rigorous testing to make label claims of pest and disease reduction.

The fact that many biostimulants often act in multiple ways also adds to the complexity. Seaweed based products for example often contain plant nutrients but those marketed as biostimulants often act to de-stress crops. Chitin based products may directly upregulate plant growth but can also act as elicitors and switch on the plant’s own defence mechanisms. But if products are marketed as biostimulants they should not be primarily fertilisers or pesticides.  Common examples include seaweed extracts, chitin products, microbes, nematodes, phosphites and anti-transpirants. They could be applied directly to the plants or they could be targeted at the soil to improve or enrich the mycorrhizal fungi in the root zone which live in a mutually beneficial relationship with the crop roots, gaining key minerals from the plant but contributing farm more by increasing the absorptive capabilities of the roots. But not all plants form strong relationships with mycorrhizal fungi – so for example in oilseed rape that type of product is less likely to be helpful.  We have much to learn about the specifics of the biostimulants, crops and situation in Scotland where they will help. Many have been developed for horticultural settings which is not to say that they will not work in agriculture but field soils and their microbial communities are vastly different to controlled environments and composts.

Ramularia in barley is a disease that we know is strongly influenced by the stress the crop is under and where biostimulants could help to make the plant more tolerant and this is an active area of interest. The key with biostimulants is to look carefully at the label claims and use them only where the benefits are clear and the crop situation matches what the label is claiming. Pay particular attention to instructions on how to use as them – for example microbially based products might not integrate well with certain pesticides. This will be an exciting area going forward.

Fiona Burnett (SRUC) for the Farm Advisory Service

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