Pyroligneous acid, also called wood vinegar or wood acid, is a dark liquid produced by the destructive distillation of wood and other plant materials. The principal components of pyroligneous acid are acetic acid, acetone and methanol. It was once used as a commercial source for acetic acid. In addition, the vinegar often contains 80-90% water along with some 200 organic compounds.
Modern research on the use of wood vinegar was first carried out in Japan in the early 1950s. It was reported to be effective against: rosette or green mosaic in wheat, nematode in sweet potato, tobacco mosaic, powdery mildew in leafy vegetables, leaf miner and other insect pests. However, due to the introduction of agro-chemicals and their instantaneous effects, research on wood vinegar took a back seat. Ten years ago, interest in wood vinegar resurfaced as the effectiveness and safety of agro-chemicals were put on the spot. It is now commonly used by Japanese farmers and is also catching up fast in Taiwan and Korea.
It is estimated that wood vinegar contains more than 300 constituents such as acetic acid, methanol, phenol, ester, acetals, ketone, formic acid and many others. Instead of the specific effectiveness of a certain element, in the case of wood vinegar, various elements work synergistically. Various factors are controlled by the dilution rate of the wood vinegar. It has a bactericidal effect as well as the ability to propagate microbes. It has radicational qualities, which provides a growth inducing effect. But depending on the concentration of the mixture it can also be used to retard the growth of the plant.
The various elements in the wood vinegar work as co-enzymes or catalysts. Various enzymes are involved in reactions such as cell multiplication. The functions of the enzymes are assisted by the elements in the wood vinegar which co-ordinate the reactions and the cell multiplication. Elements that are effective as co-enzymes and catalysts require only a minute amount. It is like vitamins in our bodies. The dosage of some of these elements is effective in the unit of PPM. (Parts per million).
Wood vinegar contains a small amount of nutrients directly taken in by the plants. It also contains very few elements that have the bactericidal and anthelmintic effect. It is neither a fertilizer nor an agro-chemical. Yet when it is correctly applied, it enhances the intake of fertilizers and reduces the damages by various diseases. Wood vinegar enhances rooting, helps in the regulating of the nutrients condition of the soil, and the balance of the microbiological population. The changes in the microbiological population not only greatly reduce the tendency of soil bound diseases, it also increases the vitality of the roots and hence enable better uptake of nutrients.
Wood vinegar had been long known to be very effective against nematodes. It kills nematodes directly as well as propagates microbes that feed on them. The high acidity, methanol and phenol content have strong bactericidal effect at a high concentration, such as 50 to 100 times dilution. However, microbes propagate well when it is diluted to 200 times dilution. This is mainly due to the effect on the metabolism by its main element, acetic acid. Acetyl co-enzyme is produced by plants and microbes from acetic acid. Through the TCA cycle, acetyl co-enzyme is converted into citridic acid, malic acid, fumaric acid, succiric acid and other elements that are necessary for the plant and microbes. This is the main reason behind the propagation of microbes.
Through foliar application, some bacteria are killed by direct contact and the changes of the microbiological population deter the propagation of pathogenic bacteria. The acidity on the leaves surface also deters propagation. However, the most remarkable effects of foliar application are the increase in resistance of the leaves against pests and diseases and the increase in the effectiveness of agro-chemicals.
Through foliar application of wood vinegar, the leaves become shiny and darker in color. This is due to the increase in chlorophyll through the effect of ester in the wood vinegar which promotes photosynthesis. This ester also helps in the formation of sugar and amino acids. This also results in a better taste of the produce. The healthier leaves naturally have a stronger resistance against pests and diseases.
Five plant hormones are closely related to the growth and health of a plant. These are: gibberellin, cytokinin, auxin, etherlene and abscisic acid. Etherlene and abscisic acid contribute to the plant’s resistance against diseases and attacks from bacteria. An amino acid called methionine effects the formation of etherlene. The formation of etherlene is reduced by the excessive intake of nitrogen. On the other hand, growth hormones like gibberellin, cytokinin and auxin will be produced. As a result, the size of the plant increases but the resistance against diseases is reduced. The formation of oxidized etherlene from etherlene and the formation of methionine is accelerated by acids. The wood vinegar helps in their formation due to its acidity.
Furthermore, wood vinegar accelerates the process of transformation from nitrogen to amino acids. In other words, nitrogen is effectively transformed into amino acids. This will also stabilize the formation of methionine. As the result, oxidized etherlene is also produced. These processes contribute to higher plants resistance against various diseases.
At 500 times dilution, wood vinegar can reduce the cluster value of water to 1/3. This means that the water is activated and can be easily absorbed by the plants because water with a low cluster value is in a very small mass. Each of these masses will hold one or few mineral elements. These elements can be easily taken into the plants.