Wood vinegar has been widely used to repel insects from plants and housholds in Thailand and it is easy to find pyroligneous products marketed on the Internet as an insect repellent. Strong in 1973 reported good results when wheat seed were treated with hardwood tar oil to repel birds, rodents and insects. Hardwood oil was also found to be toxic to all the tested insects. Very similar effects were found when pyroligneous acid was used for controlling insects from sweet corn plots. Wood tars pyrolysed from alder, larch and birch were effective repellents for control of the vole (Clethrionomys rufocamus bedfordiae) in an experiment in Japan. In addition, scientific evidence reported in Finland demonstrated that birch tar oil effectively repelled slugs and snail.
The potential of botanical oils for insect control is well known and botanical insecticides have become increasingly utilized especially in developing countries. Wood vinegar exhibitied high termiticidal activities against the Japanese termite and the authors concluded that an ortho substituent of phenol played and important role in termiticidal activity. Preliminary investigation in Greece showed that one spray application with birch tar oil killed 95% of aphids on egg plant in a greenhouse experiment. The results of a project in Finland revealed th at the birch tar oil may repel egg laying psyllids but not flies. Beetles and mites could not be controlled with the oil and it was also non-toxic to predatory mites. Information on wood vinegar application with husbandries suggests repellents of flies, tick and fleas and killing of external parasites.
Wood Vinegar as a Repellent and Insecticide
Essential oils are dknown to be effective herbicides. Similarly birch tar oil has shown herbicidal effect on numerous species of weeds. A preliminary field experiment indicated that pyrolysis liquids made of birch wood can be used for the control of broad leaved weeds. Wood vinegar at high concentrations can kill plant cells and low doses may stimulate plant growth.
Field experiments conducted in China have shown that wood vinegar, made from biomass residues, can be used as a foliar fertilizer improving the yield and quality of celery. A mixture of charcoal and pyroligneous acid has also shown to enhance soil fertility and the growth of bedding plants. Bamboo vinegar is known to simulate plant growth depending on the pyrolysis temperature. Treatments with bamboo vinegar have also demonstrated an increase in vegetable growth. Other studies have concluded that wood vinegar in organic farming can have variety of applications, including pest control, improving soil fertility, and plant growth promoter or inhibitor. A substantial number of claims have been presented in the form of commercial advertisements, which indicates that more research is urgently need to improve the scientific basis of the use of wood vinegar in agriculture.
Wood Vinegar as Herbicide and Plant Growth Enhancer