Four weapons in the organic farmers’ arsenal that EVERY FARMER should know about!

Updated: 5 days ago

While some think organic farmers forego all pesticides, this is not the case at all. And, in fact, there are approximately 30 compounds that are permitted for use in organic farming to control pest and diseases.

Most of these compounds are not on the radar of conventional farmers or even a lot of organic growers for that matter! This is because products containing them are not massive money makers for the multinational pesticide manufacturers. As such these products are not marketed to farmers or talked about at trade events. Plus, they are organic, so surely can’t be that effective, right? And while that might be true for some of these compounds, some of them are EXTREMELY effective pesticides. For this reason we at Eutrema feel every farmer should consider using select ones as part of any pest and disease control programme. This is particularly the case for the four products listed below, which have exceptional potential for UK crops, especially as the number of conventional pesticides being approved declines.


Chitosan is a biofungicide approved for use in farming under Basic Substance regulations.

Chitosan is the soluble form of chitin, the polymer that makes up the bulk of every insect’s pests’ exoskeleton. Chitin is also the principal component of the cell wall of every fungal pathogen. However, neither chitin or chitosan are found in any plant. As such, plants have evolved to detect chitosan and use its presence as a signal that a pest or pathogen is attacking.

Plant cell membranes contain specific sensors designed to be activated by chitosan. These sensors turn on the plant’s defence mechanisms that prevent an attack (see diagram below). However, many pathogens have further evolved other compounds that mask their presence and deactivate the cell membrane sensors. This results in the pathogens using a kind of stealth mode in the plant-pathogen arms race! This is how biotrophic pathogens, like mildews and rusts, establish themselves. In fact, in many cases the plants have the biochemical armour to defend themselves, its just that they don’t know the pathogen is there. It is at this point that chitosan comes in like a nuclear warhead (I thought I would continue the war analogy). A foliar application of chitosan biofungicide completely overwhelms any attempt by a pathogen to keep the plants defence mechanisms turned off. Even if a pathogen is not present, you can prime the crop to turn its defences on in anticipation. For this reason chitosan can work as both a preventative and curative fungicide.

This mode of action makes chitosan very different to the directly biocidal fungicides a conventional farmer will be used to handling. However, that is not to say that it is any less effective!

Chitosan is also one the few cationic (positively charged) polymers found in nature, which lends itself to other uses, such as flocculating algae out of ponds and removing contaminants from waste water.

At Eutrema we manufacture an extremely concentrated (viscous) soluble concentrate of chitosan, with a long shelf life. Beware of pale imitations offered by other suppliers. Also be wary of purchasing powdered chitosan, which is theoretically soluble in water, but requires specialist knowledge and dedicated manufacturing machinery to produce a stable solution.

You will also find other products on the market that activate plant defence mechanisms, such as seaweed extracts. However, the intensity of the response is far greater when using chitosan as the lock and key chemical structure needed to activate the cell membrane sensors is specific to chitosan. As such, we recommend seaweed extracts be used more as a biostimulant during crop establishment where they excel. Plus, seaweed extracts are not permitted for use for pest and disease control in the UK and EU.

Lime Sulphur

It might seem strange that such a powerful and hazardous (to humans) chemical is allowed to be used on crops, never mind organic crops! However, it is, and it works wonders. Lime Sulphur contains ‘calcium polysulphides’, and is a powerful sterilising agent for plant tissues, so is great for curing foliar diseases. Especially stubborn ones that you may struggle to get under control with other fungicides. It will also kill any pests that comes into contact with it. The active ingredients readily break down to a non-hazardous from, so you do not need to worry about its hazardous nature, once you have safely applied it to the crop.

Once Lime Sulphur has finished acting to control pests and diseases, the calcium and sulphur in the product quickly converts to form plant-available nutrients. This is especially useful as the sulphur is in an alkaline form, not acidic (as is the case with powdered sulphur).

Lime Sulphur can be used in a dilute form as a foliar spray, or at a stronger dilution directly to the soil before planting. As well as acting to kill pests and pathogens, and adding nutrition, the calcium in Lime Sulphur will also have a mild flocculating activity on the soil. I know what you are thinking; ‘where have you been all my life Lime Sulphur?’!

With so many fungicides not working against blight and root rots, we would recommend any farmer seriously consider the use of Lime Sulphur as part of their spraying programme. With rising levels of fungicide resistance developing for nearly every crop disease, why wouldn’t you at least consider an extra weapon to introduce to a spray programme to improve control and reduce the risk of resistance to conventional fungicides?

I want to be honest with you. There is one major downside of using Lime Sulphur. And that is the horrid smell; it smells of rotting eggs! As such, you need to handle, store and transport the product in a safe manner (as outlined on the label and in the safety data sheet). However, when we have spoken to farmers using our product they actually rave about it for this very reason! The fact that it is bright orange, smells revolting, and has hazard warnings on it, actually gives them confidence that it is going to work! It’s not just another organic dirty brown liquid in a bottle :D

In fact, while Lime Sulphur is hazardous, it breaks down into a form that is non-hazardous to humans and of benefit to the crop. You can contrast this with the many copper-based fungicides on the market, many of which are permitted in organic farming. Copper is hazardous, but unlike Lime Sulphur, copper remains in a toxic form long after application. Plus repeated applications of copper can build up concentrations in the plant and soil that are toxic to plants and soil health. So combined with the questionable safety on edible crops, we feel Lime Sulphur is a far better choice for disease control in most situations.


This insecticide is an extract from the Neem Tree that grows on the Indian subcontinent. The tree is in the mahogany family, but it is prized from the oil extracts from the seeds, not its wood.

Neem oil has a long history of use in both traditional medicine and pest control in crops. Azadirachtin is the chemical within the oil that is active as an insecticide. However, rather than being directly biocidal to the insect, it acts primarily as an antifeedant. As a result crop pests die of starvation.

Because it is acting as anti-feedant and not a biocide, Azadirachtin has very low mammalian toxicity and is readily biodegradable. This combined with its natural origin, is the reason organic farmers are allowed to use it.

Azadirachtin is particularly effective against thrips, so any conventional farmer not considering using it is really missing a trick. This is especially the case as populations of thrips are set to increase in the British Isles with climate change creating milder winters that allow for over-wintering populations of Western Flower Thrips which were not present previously. Plus thrips are an important vectors for many pernicious plant viruses.

Insecticidal soaps

Kind of does exactly what it says on the tin; contain soaps that kill insect pests! Despite being synthetic chemicals (fatty acid salts), they are permitted organic farming because they have a physical mode of action, not a biocidal activity as with conventional insecticides. The soap strips the wax from the insect’s exoskeleton that is essential to preventing dehydration. This results in pretty much the instant death of the pest.

This all sounds great, but the use of insecticidal soaps has been limited due to unwanted scorch / phytotoxicity to the crop. This happened because those products on sale to growers have been almost exclusively based on cheap sodium lauryl sulphate. As a result, the crop gets damaged from the toxic sodium delivered before the pest is effectively controlled. To prevent this, Eutrema Insecticidal Soap contains no sodium. This means that the dose rate can be higher; to the point where it effectively controls the pests while not harming the crop. We particularly recommend Eutrema Sodium-free Insecticidal Soap for use against sap-sucking pests, such as aphids. Many organic farmers use Insecticidal Soap in combination with Azadirachtin as it has been repeatedly shown in academic trials that these two compounds potentiate each other’s activity.

There are three extra advantages of using these four compounds in pest and disease control:

  1. They can be used on pretty much any crop without restriction. This is particularly useful for niche but high value crops where conventional pesticides have not been given authorisation.

  2. Most can be used from sowing all the way up until the day of harvest with no minimal residue levels.

  3. They are, more often than not, more cost-effective than using patented pesticides from the multinationals.

Table of how to use each of the four products discussed in this blog:

Details of active ingredients that can be used in organic farming can be found here:

The list above does not cover microbial biopesticides. While there is no list of approved microbial bio-pesticides, it is possible to search the HSE pesticide database for the active species, such as Bacillus, Trichoderma, or Beauveria:

If you would like to know more about these, or any other organic pesticide, biostimulant, or crop nutrition product, then please get in touch with our technical team. We offer trial size packs of all these products on our website, and we can provide technical guidance in setting up an on-farm trial to showcase their ability to protect and enhance your crop yields.

Dr Russell Sharp

Eutrema Ltd

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