Dr Gerhard Verdoorn
Operations and Stewardship Manager
Humankind is slowly moving towards greener living which should be more compatible with the natural environment. Fossil fuels are being frowned upon, agricultural production by conventional methods is no longer the flavour of the month and pressure is mounting against “chemicals”, while very few people realise that the Universe is one enormous chemical factory.
There is nothing that is not chemistry. Protagonists of a “greener world” want all “chemical pesticides” to be replaced by natural and biological pesticides. It sounds great, but those very individuals express their ignorance by preaching that natural and biological is safer than chemical and man-made.
Fact is that many of the current chemical pesticides that are widely used are synthesised by none other than Mother Nature: abamectin, matrine, azadirachtin, spinosad, gibberellic acid and pyrethrins are examples of natural metabolites produced by biological organisms. Humankind developed technology to beneficiate such substances from plants, yeasts, bacteria and fungi for plant protection. The question is, where do they fit into plant protection? How effective are they? And do they need some form of regulation?
Efficacy, safety and regulatory requirements
There is a very bold tendency in the biological and natural pesticide arena to claim super efficacy against a wide range of target organisms. The truth is that biological pesticides are effective when applied within a particular set of climatic conditions. When these conditions are not optimal, they reduce the efficacy of the substances, often to disappointing levels which leads to a distrust in biological and natural plant protection products.
A factor that plays a very important role in the performance of biological and natural plant protection products is the quality of the products. The quality is determined by the strain of the live organism, its purity and the matrix or formulation in which it is offered. It is very easy to make a claim about an organism’s efficacy, but a totally different story to prove its quality. The same goes for natural chemicals that are marketed as plant protection products. There are factors to consider when working with natural and biological plant protection products, namely –
The species, sub-species and strain of the organism
Many of the biological products that are currently registered as plant protection products are selected from a range of sub-species and most often a particular variety or strain of that sub-species. This is a critically important aspect because biological organisms produce their own endotoxins that kill the target organisms.
Bacillus thuringiensis for example, produces proteins that, when eaten by insects, are activated in their gut and kill them. These protein toxins cannot be activated in mammal intestines and therefore do not affect people. Microbes (the collective term for micro-biological organisms including bacteria, fungi, yeasts and viruses) have the ability to mutate easily and if the incorrect mutant is used as a plant protection product, it may have two possibilities, namely (1) produce an unknown metabolite that may be very harmful to people or (2) not produce any metabolite of any use as a plant protection product.
The purity of plant extracts that contain natural chemicals used as plant protection products
Many plants such as the neem tree Azadirachta indica and chrysanthemums Crysanthemum cinerariifolium produce very useful secondary metabolites such as azadirachtin and pyrethrins that are proven natural insecticides. The extraction of these active ingredients from the plant oils requires great skill to ensure the final product is of high purity and does not contain harmful substances. It is known that neem oil that is not properly purified may contain aflatoxins, some of which are highly carcinogenic. Although azadirachtin is a very effective insecticide with a very favourable environmental profile, it may be contaminated by a deadly carcinogen.
The quantity of the units in the matrix or formulation
Biological organisms such as the various Bacillus strains, entomopathogenic viruses and nematodes, and Trichoderma fungi are measured in international units per milligram and not in mg/kg or mg/ℓ as for the classic chemical pesticides. Poorly cultured yeasts, bacteria and fungi may not have the optimised number of international units and will therefore not produce the expected results.
The stability and shelf life of the matrix or formulation
Formulating and packaging a biological plant protection product is more onerous than the same development for a chemical plant protection product. Since they are live organisms, they must generally be formulated in highly sterile conditions and packed in special hermetically sealed packaging to prevent oxygen and moisture from destroying them, while packaging must block out light to prevent solar decomposition.
This is still quite a challenge for many biological products while purified natural chemicals face much less of these pressures. Natural plant extracts that contain the natural chemicals are different though and also need special packaging to prevent the harmful effects of moisture, oxygen and light.
The Fertilizers, Farm Feeds, Seeds and Remedies Act, 1947 (Act No. 36 of 1947) does not differentiate between synthetic chemicals, natural chemicals or biological organisms when it demands that all such substances and organisms are registered. The definitions of an agricultural remedy (pesticide or plant protection product) in section 1 in fact specifies any chemical substance or biological remedy or any mixture or any combination of a substance or remedy intended or offered for…. It is evident from this definition that the Act is overarching over all substances or organisms that are perceived to be plant protection products. Section 7 prohibits the sale of any agricultural remedy unless it is registered under the Act.
Unregistered biological and natural pesticides
Many manufacturers of biological plant protection products market their products without valid registration. This means that their products have not undergone the rigorous testing required by the articles and regulations of Act No. 36 of 1947 for, amongst others, efficacy, crop safety, human safety, environmental safety and stability. A person who buys and applies such unregistered biological products has no idea whether the product is what the manufacturer claims it to be, has no guarantee that the product will perform as expected, no idea whether the product contains harmful contaminants or impurities such as aflatoxins, has no idea what the shelf life of the product is and basically puts his crop, and the consumer who buys and eats the produce, at tremendous risk. The purpose of registration is for the regulatory authorities at the Department of Agriculture and Department of Health to ascertain whether the biological product is effective, but most of all whether it holds any risk for human health and the environment.
Unregistered biological organisms are sometimes smuggled into the country from abroad, while the Directorate of Plant Health requires that all such foreign organisms be put through a risk analysis programme. The world has seen what a virus like the latest SARS CoV-2 that caused the Covid-19 pandemic can do. Keep in mind that Bacillus is a genus of bacteria that harbours not only the extremely valuable B. thuringiensis species and its various strains, but also the deadly B. anthracis that causes anthrax. To think that biological is always safe may be a fatal thought if the organism that you work with has been identified incorrectly. All facilities that work with microbes such as Bacillus, must be registered under the Non-proliferation of Weapons of Mass Destruction Act, 1993 (Act No. 87 of 1993) as a measure to govern the cultivation and use of microbes. It sounds like an overkill, but biologicals of unknown identity can have a devastating effect on people and the environment.
The wonders of properly manufactured and registered biological plant protection products
Many South African and international companies offer registered biological plant protection products for agriculture and even for home garden use. These products have undergone rigorous testing and are formulated to give excellent control of plant pests. It helps food producers to move away from total chemical pest control to integrated pest management and offers consumers an assurance that food safety is as important to producers as it is to consumers.
It does, however, demand a mind shift to adapt to the requirements for using biological plant protection products effectively, but the rewards are vast. One of the main hurdles in the agricultural mindset is the demand for immediate results; biologicals do not act as fast as hardcore synthetic chemicals, yet upon being in contact with the target organism, they mostly terminate feeding which means the crop is saved immediately, although the target only dies a few hours or days later.
Signs and symptoms of unregistered biological plant protection products
Any plant protection product that is offered for sale in South Africa must have a registration number starting with a capital L followed by four or five numbers, e.g. L1234 or L12345, and have the exact scientific name of the organism, plus its concentration depicted as IU per mg. If this information is lacking, the red flags are already flapping in the storm. If a biological remedy’s manufacturer makes vast claims about efficacy against virtually all plant pests, it is a blatant false claim because biological plant protection products, like their chemical counterparts, can never be effective against all plant pests. The manufacturers of unregistered biological products often claim their products are non-toxic and safe for human health and the environment. Be weary of such claims. If it is of this nature, then why is it not registered to substantiate that claim? Another false claim is that the unregistered biological product can replace all chemicals. So, if the biological replaces all chemicals, what about the endotoxins that are produced by the unregistered biological product? Are those not chemicals? Producers should be vigilant when it comes to using crop protection products of any nature. If an unregistered biological product is used, be sure to know that your produce is likely to be rejected by the markets and consumers.