Biocontrol plant protection products

Biocontrol products and pest control.

Biocontrol crop protection products containing potassium bicarbonate (potassium hydrogénocarbonate).

The use of sodium or potassium bicarbonates as fungicides in agriculture is not a new idea. Their use dates back to the beginning of the twentieth century. They act by inhibiting the formation of the mycelium of fungi after spore germination. They are therefore not chemical substances that kill pathogenic fungi as synthetic fungicides do. They simply hinder their proliferation, which requires several applications throughout the crop cycle, especially to untreated areas, otherwise infection will resume. For this reason, treatments with sodium or potassium bicarbonates can be disappointing, especially in rainy areas. Treatments with sodium or potassium bicarbonates require that sprinkling be stopped.

In the presence of water, the sodium or potassium bicarbonate molecules quickly dissociate into sodium or potassium ions and bicarbonate. Potassium bicarbonate is preferred for three reasons:

•

It causes less burning of the foliage than sodium bicarbonate.

•

Sodium bicarbonate breaks down in the soil leaving sodium ions that can destructure CAC (see article on clay-humus complexes)

•

Potassium bicarbonate rapidly dissociates into potassium and bicarbonate ions. These ions are part of the natural nutrient cycles of living things.

Potassium bicarbonate is not harmless. Excessive dosing can burn the leaves. The dosage should not exceed 0.5-1% (i.e. 5-10 g or 1-2 teaspoons per litre of water), in total bicarbonate content. The solution should be sprayed as evenly as possible on both sides of each leaf and on the whole plant so as to cover all organs with a thin film, but without producing excessive drips. The application should be made as a preventive measure, especially if other nearby plants are already affected. Repeat application should be made after heavy rain and after the plants have dried. Each application should be spaced at least one to three weeks apart depending on local conditions.

Although not considered toxic, bicarbonates can have adverse effects on soil fertility. Excessive use can lead to calcium and magnesium deficiency due to the formation of insoluble carbonate compounds. Iron absorption can also be impaired and lead to necrosis. Applications of potassium bicarbonate should be stopped at the first sign of phytotoxicity or when a decline in flowering quality is observed.

Potassium bicarbonate can be purchased in specialised garden centres or on websites, e.g. by clicking here.

Bacillus subtilis str. QST 713

This bacterium stimulates the natural defences of crops by counteracting the attachment of pathogenic fungi by perforating the membrane of their mycelium. To be used as a preventive treatment (pome fruits, stone fruits, tomatoes, lettuce, cucumbers, courgettes, etc.); sold in garden centres and on websites under the trade name "Natria" - or here or "Solabiol". It is one of the only microbial treatments against cryptogamic diseases available to amateur gardeners and should be applied every 7 days as a preventive measure on tomatoes and cucurbits instead of Bordeaux mixture.

Bacillus thuringiensis (Bt).

Bacillus thuringiensis, better known as the Thuringian bacillus, is probably the most widely used microorganism in biological control. This ubiquitous aerobic bacillus is abundant in nature. It is present in soil, water, air and on plant foliage. Its reputation in organic agriculture is due to its ability to multiply in cultivation, its storage in containers for easy marketing, its highly selective targeting and its competitive price.

Bacillus thuringiensis synthesises a protein crystal during sporulation. After ingestion by the insect, this protein crystal releases protoxins which, in the presence of the insect's digestive proteases, are transformed into active polypeptide toxins. These enterotixins bind to specific receptors located on the cells of the insect's intestinal epithelium causing large legions of the intestine resulting in paralysis of the digestive tract. The insect can no longer feed and death occurs within 24 to 48 hours. There are more than 50 varieties of Bacillus thuringiensis, some of which are marketed.

In vegetable growing, Bacillus thuringiensis is used against the leek moth, which can also attack garlic, onions and shallots. Bt is also used against other polyphagous caterpillars that parasitise artichokes, cardoons, beans, tomatoes, aubergines and cabbageworms. After dilution in water, the solution is sprayed on the leaves and stems, making sure to cover all aerial parts. This treatment must be repeated 8 to 10 days later to neutralise the larvae from the last generation.

Bacillus thuringiensis is safe for other animals, humans and plants. The bacteria die and degrade without leaving a toxic residue. It is important to note that the effectiveness of commercially available preparations depends very much on a number of factors such as climatic conditions, local biotope, treatment methods and concentration of the product. Success would not be assured if the manufacturer's advice on the use of the products is not followed to the letter.

The subspecies kurstaki (Btk) and aizawai are specific to the larvae of lepidopterans (butterflies), many of which are pests of food and ornamental crops. Btk is generally considered environmentally friendly, as its toxicity is essentially limited to its target organism. Humans, wildlife and beneficial insects are considered unaffected by Btk. However, in 2012, a review of several Bt strains by the European Food Safety Authority stated that there was insufficient data to definitively confirm the claims of low toxicity (5). Treatments are most effective when applied against the youngest larval stages. The crystals have a very limited life span (48-72 hours) and are destroyed by UV light and can be washed away by rain or watering equipment. However, the products on sale in garden centres contain additives that allow them to last a week or so.

As Bt affects the digestive tract of insects, its use against sucking insects such as aphids and mealy bugs is very limited. In addition, the intensive use of this bacterium risks producing resistance. This is a well-known phenomenon in medicine. This is how, for example, resistance to antibiotics arises from overuse. Several strains of insects resistant to bacillus thuringiensis have been reported, first in 1985 (McGaughey (7)). Resistance cases are so far few and often recessive. The majority of resistance cases have arisen in the laboratory.

It is important to note that the effectiveness of microbial products is still uncertain. Once the microorganisms have been introduced into the crops, they are subject to various biological and abiotic constraints that more or less determine the success of the biocontrol mechanisms.

Plant protection products containing esterified rapeseed oil.

Preparations based on mineral paraffin oil are mainly used against the mealy bug. Its contact action suffocates eggs, larvae and adults. These preparations should not be used in the presence of pollinating insects or useful auxiliaries (bees, bumblebees, ladybirds, etc.). On sale in garden centres and on websites under various trade names, some of which are reserved for professionals.

Esterified rapeseed oil acts on many pests, including phytoptes (mites invisible to the naked eye). The oil film stops oxygen from penetrating the breathing organs and the insect dies of asphyxiation. No resistance phenomenon has been demonstrated to date. Different trials carried out in France have shown that a preparation containing emulsified rapeseed oil sold under the trade name "Aturen Eradibug" is effective against aphids in vegetable and fruit crops. 7 trials showed very good efficacy on aphids compared to a synthetic insecticide (bifenthrin), provided a second application is made. The product is also effective against mites with a higher result than the reference synthetic insecticide. Other trials showed good control of whitefly and mealy bug (8).

Trials on vegetable crops showed no phytotoxicity following two single and double dose applications. This multipurpose plant insecticide controls eggs, larvae and adults. This product is sold in garden centres and some internet sites. Apply taking care to wet all leaves and stems thoroughly and repeat the treatment after 7 to 14 days. Do not treat in the presence of bees or apply this product to plants in flower. On the E-phy website it is stated that this product can harm the auxiliary fauna.

I have noticed, but this needs to be verified, that the esterified rapeseed oil sold by the Naturen company is effective against the Colorado beetle at the maximum dose recommended in the instructions for use, i.e. 30 ml/per 10m² and 1 litre of water in a sprayer.

Tip:

Here is a cheaper home-made preparation based on rapeseed oil which would have an equivalent effect. Prepare a solution containing 2/3 rapeseed oil and 1/3 dishwashing soap. Shake vigorously to obtain an emulsion that can be used as a spray at a rate of 20 to 30 ml of the emulsion per 10 litres of water.

Plant protection products containing maltodextrin.

Maltodextrin is a polysaccharide used as a food additive. It is produced from vegetable starch by partial hydrolysis and is usually found as a white hygroscopic powder that is spray-dried. Its use as an organic pesticide is quite recent. Maltrodextrin acts in the same way as rapeseed oil.

Plant protection products containing mineral paraffin oil.

Plant protection products containing sulphur.

Courgettes, cucumbers, pumpkins... are very sensitive to powdery mildew caused by certain ascomycete fungi. This rapidly spreading fungal disease is characterised by the appearance of a white powder covering the leaves (hence the name "powdery mildew"). Several natural methods are known, such as decoctions of garlic or horsetail, but I have never seen convincing results with these products.

Sulphur in liquid or spray form is known to control powdery mildew, including that which infects fruit trees. I have found that sulphur is very effective against powdery mildew on some susceptible fruit trees (such as golden delicious), but it has the disadvantage of acidifying the soil. It is oxidised to sulphuric acid by micro-organisms such as those of the genus thiobacilus. The rate of oxidation depends largely on the size of the particles. The powder form used against powdery mildew is the most active (9). There are many preparations for professionals and some are approved for private individuals (such as kumulus jardin, Microthiol spécial jardin, Sofluid DP jardin...). Available in garden centres and on websites.

Pheromone traps.

Pheromones are natural, volatile substances secreted by insects and certain animals. Each type of insect pest has its own specific pheromone, which is often emitted by the female to attract the male, who can detect it several kilometres away. The principle of the treatment is to use a glue trap equipped with a diffuser imitating the female's pheromone. Imprisoned in the trap, the male cannot then mate. Another technique is to introduce a pesticide into the trap to kill the pest attracted by the pheromones (attract and kill technique). The production of the pest is then stopped. Traps containing pheromones and pesticides are only available to professionals.

For the garden, there are pheromone capsules that can be placed in traps sold in garden centres or on certain websites. The capsules on sale to private individuals are said to neutralise the carrot, parsnip and celery worm, the leek, garlic and onion moth, the wireworm, the tomato and cabbage cutworm, and the highly polyphagous leafroller which causes considerable damage in vegetable and fruit crops. Pheromone traps and capsules (prices range from €15 to €40) are available in garden centres or by clicking here. These traps should be placed as early as April before the predicted attack of the pests and it is strongly advised to place several of them.

Plant protection products Ferric phosphate (iron orthophosphate).

This molluscicide (slug killer) is well known in garden centres and is sold under various trade names. It comes in the form of baits that are effective against a large number of snails and slugs. It has the advantage of being animal-friendly. However, it also attracts ants, which drag it into their nests. Some home gardeners combine it with a low dose pyrethroid to avoid this problem.

Plant protection products potassium salts of fatty acids.

This preparation manufactured by a French company is a fungicide and insecticide in the form of an aqueous solution containing sulphur and potassium salts of fatty acids as active ingredients. The latter are contact insecticides acting on the permeability of the insect cuticle. These substances are considered to be environmentally safe. Reserved for the treatment of the aerial parts of indoor plants, balconies, terraces, gardens, etc. It is a preventive or curative product to fight the following insects and diseases: Aphids, mealy bugs, whiteflies, powdery mildew, leaf spot diseases. Sold under the name "CPJ INSECTS AND DISEASES". There is a preparation containing only potassium salts of fatty acids sold under the name "CPJ Aphids" for the control of aphids on indoor plants. Available by clicking here.

Plant protection products aluminium silicate.

Cherry fly and olive fly attacks can be limited by a physical barrier based on white clay. Some products are limited to professionals. The preparation called "Argi-jardin" is intended for private individuals.

Plant protection products viruses.

Some viruses parasitise pests. They are not dangerous for humans. Preparations containing these viruses are mainly reserved for the treatment of some varieties of fruit trees. Their use is authorised when no bees are present. Preparations are now available for the amateur gardener who has a few fruit trees. The product acts by ingestion. The target larvae are codling moth and Oriental fruit moth. The larvae become infected by ingesting the virus when they feed on the treated leaves. The virus then multiplies in the larva's body, causing anorexia and death. This product is sold under several trade names (CARPOVIRUSINE, MADEX PRO).

Biocontrol crop protection products containing nematodes.

Nematodes are small microscopic worms that live naturally in the soil. Some of these nematodes parasitise vegetable plants, and others are predators of pests. The latter are therefore very interesting for reducing populations of insect pests, slugs and snails, cutworms that eat roots, ants, Colorado potato beetles that eat the leaves of potatoes, etc. The beneficial nematodes move around in the soil in search of their prey to reproduce. An infected pest eventually withers and dies. The nematodes then go in search of new prey. These beneficial insects only infect certain pests and are harmless to humans and domestic animals. As the nematode population is often insufficient to control pests, increasing the density of nematodes in the soil by importing a nematode culture increases the protection of vegetable plants (preventive or curative). However, this preventive action, which lasts a few weeks, depends on several factors such as soil moisture and temperature.

Nematodes are sold in the form of a powder to be diluted with water and poured into a watering can to treat vegetable plants, or in a sprayer for fruit trees. The soil or fruit trees must be moistened beforehand. The humidity of a fruit tree must be maintained for a few days.

Some nematode cultures are specific to slugs and are effective in protecting salads and strawberries. Other nematodes are able to reduce codling moth populations that infect apples, pears and walnuts. There are also traps with nematodes that can protect raspberries, strawberries, olives and ornamental shrubs against the otiorhynchus (Otiorhynchus). This pest is a small, flightless, nocturnal weevil, black or dark brown in colour. They have a rostrum on their head and 2 long club-like antennae at the end. It is a plant pest both as an adult and as a larva. For more information on this bio-aggressors, click here.

For more information on the use and purchase of nematode cultures, click here.