Introduction to integrated methods in the vegetable garden
Chapter : Biocontrols
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⇒ Integrated Biological Protection ; first approach.
For more than 50 years, the development of the chemical industry has provided an effective response to crop-threatening pests becoming an essential modelhas and widespread model for plant protection. Fertilisers and pesticides have enabled high yields to be achieved to meet the growing world population (a). But pesticides have a negative effect on the environment and have eventually selected for bio-aggressor that are resistant to the molecules on the market. These pesticide resistances have also developed in the vegetable garden; for example, the green aphid Myzus persicae, some strains of which survive neonicotinoids and pyrethroids (and related molecules; the pyrethrins approved for organic farming) (1). This aphid, which likes peaches, is very polyphagous and is content with at least 50 botanical families, including cucurbits (cucumbers, gherkins, etc.), solanaceous plants (potatoes, etc.) and brassicas (turnips, etc.). Research was then directed towards less aggressive alternative solutions: selection of varieties more resistant to diseases, biological control by spraying predators of bio-aggressors, use of traps containing hormones, etc.
Nowadays, we no longer treat crops blindly with multipurpose combinations containing different plant protection products as soon as we discover a spot on a fruit or a leaf. A pest does not have to be dreadful, a disease can be benign and not require any treatment, and the removal of a diseased organ is sometimes enough to eradicate an emerging disease. Plant protection products have also been improved to reduce their dosage and to target pests more effectively, with less impact on the environment.
To reduce the use of pesticides, an overall strategy has been defined called Biological Integrated Protection (BIP) or, for fruit, Integrated Fruit Protection (IFP). BIPs and IFPs include biocontrol techniques that consist in optimising the interactions between the different components of an ecosystem in order to reduce pest pressure (biodiversity corridors, importation of beneficial insects, physical protection against insects, sterile insect technique (SIT), biocontrol plant protection products....). However, it is also necessary to take into account the formidable capacity of pathogens and pests to adapt to their environment, which sometimes requires the use of pesticides approved for use in organic farming, or even a return to synthetic pesticides.
In integrated biological protection, pesticides are used when all other methods have failed, but not under any conditions. Pest populations must exceed a threshold beyond which irreversible crop damage occurs, resulting in unacceptable economic losses. Biocontrol plant protection products, including those approved for organic farming, are used first. If this fails, synthetic pesticides are then used.
Biocontrol techniques cannot solve all the problems encountered. In addition, the farmer often has to deal with problems of use that are less flexible than those of plant protection products, such as the constraints of conserving living organisms (bacteria, beneficial insects, etc.), negative interference with other biological phenomena, and the specificity and formulation of applications.
As for professional farmers, the gardener is confronted with the hazards of biological control. They sometimes have to deal with highly contagious diseases causing considerable losses (rust, mildew, etc.) which require anticipation of attacks. But, before taking their sprayers, many gardeners should first inform themselves about the characteristics of the bio-aggressors that would threaten their crop. Confusion with beneficial insects, unnecessary treatment of infections accompanying natural ageing, physical stress mistaken for microbial or fungal infection are some examples of common mistakes made in the vegetable garden.
Most of the biocontrol techniques that can be used in a vegetable garden are described by clicking on one of the menu items at the top right of this page.
a) From 1960 to 2005, the world population increased from 3 billion to 6.5 billion and the utilised agricultural area (UAA) per capita decreased from 4,300 m² to 2,200 m² (source UN-FAO).
Home gardeners find that they are often confronted every year with invasions of certain pests (e.g. aphids, larvae that burrow into carrots). Other bio-aggressor are occasional and are more or less aggressive depending on changing factors that the gardener cannot control (such as the climate). In the same region, a cultivated plot may be commonly invaded by one or more dominant bio-aggressor that do not exist (or are less numerous) in another plot located a few kilometres away.
The existence of dominant bio-aggressors that frequently return to crops requires anticipating their attacks by starting to modify the environment (for example, plantations that favour the attachment of pest predators, etc.), installing physical protection (anti-insect nets), and providing for the importation of useful auxiliaries. Occasional pests are treated on a case-by-case basis, depending on the degree of invasion and their aggressiveness, the resistance of the crops, which varies from one species to another, and above all the cultivation method (a poorly nourished and weak crop has difficulty resisting pest attacks).
This disease is characterised by black spots appearing on the fruit, but opposite the stalk. This benign disease is favoured by too much watering, or a boron deficiency revealed by laboratory analysis, or the choice of certain very sensitive varieties such as 'Roma'.
caused by excess water.
blackening of the roots of carrots, endives, celery, melon, lettuce, tomatoes, beans, cucumbers: these are cryptogamic infections resulting from poor growing conditions that weaken the plants. To fight against these opportunistic infections, it is necessary to act on the cause and not on the consequence: excessive humidity, unbalanced or insufficient fertilisation...
black crust formed by several fungi accompanying insect bites, especially aphids, leafhoppers and mealy bugs. The fungi develop on the honeydew left by the biting insects without entering the plant. The plant is not invaded. It is sufficient to cut off the diseased parts, isolate the plants with physical protection and possibly treat the aphids if their predators are not yet present, or import aphid predators.
Some diseases considered problematic before harvesting, appear at the end of a crop cycle such as verticillium wilt and powdery mildew. It is then preferable to pull out the infested plants after harvest and before these diseases are transmitted to other more recent crops.
1) Résistance du puceron vert de pêcher (Myzus persicae) vis-à-vis des pyréthrinoïdes et des néonicotinoïdes -PLAN DE SURVEILLANCE 201 – ANSE – Ecophyto – août 2013