Fungicide

A fungicidal is a plant health Produit conceived exclusively to kill or limit the development of the Champignon S parasite S of the Végétaux. The products with medical uses are called Antimycosique S.

One distinguishes:

  • preventive products preventing the development of the spores on the surface of the plant
  • the curative products which stop the development of mushroom already installed in the plant.

For a long time, only fungicides available were products acting by contact and thus being able to be used only with preventive measure. They act indeed on the spores of mushroom before those could not emit filaments penetrating fabrics of the host.

The first systemic fungicides appeared at the end of the Sixties. They have the advantage of having an at the same time preventive and curative action.

Currently, fungicides employed come from the association of about thirty active matters gathered in several chemical families.

There exists a multitude of modes of actions which block or affect the organization of the pathogenic germs:

  • fungicides multisite (which act on several parameters at the same time)
  • those which act on breathing mitochondriale
  • those which inhibit the synthesis of sterols
  • those which inhibit the synthesis of the amino-acids
  • of others which disturb the cellular division
  • the Simulators of Natural Defenses (SDN)
  • …

These various modes of action act each one for a type of disease in particular like the septoriose, the fusariose, the oïdium, rust, root rot pours…

Fungicides are generally less toxic for the man than the two other great groups of pesticides (insecticidal and weedkillers).

Various groups of fungicides

Fungicides of contact

They operate enzymatic mechanisms implied in the energy production of the plant. These basic mechanisms meet at all the living beings, which gives to these products a broad spectrum of action. These fungicides can be divided into several families.

Products containing metals

These metals are the Cuivre, the Zinc, the Fer, the Manganèse, the mercury in the form of salts (form mineral) or combined with an organic molecule (organic form). Metal (Me+, Me++) constitutes the active part of the molecule. Metals are agents thiolprives, i.e. they set on groupings HS or Thiol S (R-SH) constituting the active part of many enzymes having a role in the phenomena of oxydoreduction ensuring the transport of energy of the plant. As we said, the toxicity of these metals is not specific to mushrooms but touches all the living beings. However, the mushroom spore has the capacity to concentrate metals enormously, thus involving a quite higher concentration the thiolprives ones compared to the other organizations from where them particular sensitivity.

Metals have the disadvantage of having a phytotoxicity with regard to the culture. It was thus necessary to prepare them in a form which reduces this phytotoxicity (organic form). The organic forms have moreover the advantage of having a better remanence, which avoids their scrubbing with the first rain.

Let us note that the compounds organo-mercuriels are very effective but terribly toxic for the man.

Sulfur

The Soufre in the form of powder is used such as it is or mixes some with the surface-active ones in the form of suspension in water. Sulfur poses problems of phytotoxicity with certain cultures when the room temperature exceeds the 30°C.

sulfur products (Carbamates)

Appeared in the Forties, the series of the Thiocarbamates and Dithiocarbamates act while releasing from isocyanates or the thirame, molecules active which block groupings HS of the enzymes, thus disturbing the metabolism of mushrooms on 3 levels: inhibition of the oxidation of glucose, inhibition of the synthesis of nucleic acid, inhibition of the degradation of the fatty-acids. The dithiocarbamates are deprived of any phytotoxicity.

Examples: Prothiocarbe, Zinèbe, Manèbe, Mancozèbe, Propinèbe, Thirame, Carbatène.

Systemic fungicides

Systemic fungicides act on phenomena of biosynthesis and are of this fact more specific. Their amount of use is more reduced than for the products of contact, generally lower than 100 G of active matter per hectare. On the other hand, because of their mode of action, the appearance of resistant mushroom stocks is to be feared. They are generally marketed mixes some with a product of contact.

Derivatives of the acid carbaric and benzimidazoles (carbamates)

Once absorbed, these products are transformed into carbendazime which is antimitotic. These products block the cellular and nuclear division (mitosis) by disturbing the formation and the operation of the chromatic spindle. This molecule has moreover one action on the level of the DNA: it replaces the purine bases (adénine and guanine) of the nucleic acids and cause errors in the transcription of the genome. However, this last property would not explain the toxicity of these products.

Specific, they are without effect on the Phycomycètes mushrooms of the kind Pythium , Phytophtora , Perenospora , Mildiou and the Pleosporaceae . They are largely used on the tropical cultures. They often cause the appearance of resistant stocks at the Oïdiums and the Cercospora .

Examples: Bénomyl, Carbendazime, Fuberidazole, Thiabendazole, Propamocarbe, Diéthofencarbe.

Systemic inhibiters of the synthesis of sterols (IBS)

It is an important group gathering in several families half of the active matters. They cause the inhibition of enzymes implied in the synthesis of sterols, involving a disturbance of operation and formation of the cellular membranes of mushrooms.

Much of them has a systemic action, but some are translaminaires (prochlorase). They are effective, between-others, against Pyrenophora spp, Venturia spp and Septoria spp.

One seeks molecules having the same toxic effect but on links different from the synthesis of sterols for, by complementarity, to limit the risks of resistance.

Examples: Imidazols: Fénapanil, Imazalil, Prochloraze, Triflumizole Pyrimidins and close relations: Buthiobate, Fenarimol, Pyrifénox, Triforine Morpholines: Aldimorphe, Dodémorphe, Fenpropimorphe, Tridémorphe, Trimorphadine Triazoles: Bitertanol, Cyproconazole, Dichlobutrazole, Diniconazole, étaconazole, Flusilazol, Flutriafol, Penconazol, Propiconazole, Triadimefon, Triadimenol, Triflumazole

Phytoalexines

See too

QoI

Antimycosique

Be-X-old: Фунгіцыд Simple: Fungicide

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