TFRI research and information on brown root rot in trees:-
(1) Brown root rot was first identified in Taiwan over 70 years ago. It is found all over the island, and attacks over one hundred species of tree. From the first yellowing of the leaves to tree death takes just one to three months, so brown root rot is classified as a blight. The fungus is mostly transmitted by direct contact between the roots of diseased and healthy trees, and transmission over long distances is rare, so its spread is fairly slow. Within a single year, brown root rot is only likely to pose a danger to the trees immediately surrounding an infected area.
(2) There is no officially recommended treatment or preventative measure for brown root rot. Research carried out by TFRI has shown that the anti-fungals tridemorph, triadimefon and flusilazole are partially effective in treating brown root rot, as are copper sulfate and urea. However, this research is not yet complete, and results have not been officially registered, so we cannot at present recommend any of these treatments.
(3) The fungus that causes brown root rot affects the roots of trees before any sign of infection is visible above ground. By the time yellowing of the leaves is seen, the roots have already been seriously damaged, and it is likely too late to save the tree. Therefore it is important to focus on prevention.
TFRI recommends the following practices.
1. Ditch separation: dig a ditch one meter deep between infected and healthy trees, lay a plastic barrier, then fill the earth back in. This will help to prevent contact and transmission between infected and healthy roots.
2. Dig up and burn the root structure of infected trees. If it is not possible to dig up all rootlets, then treat with fumigant Basamid (50-100g/cubic meter soil), or urea (2-4kg/cubic meter soil), and cover with plastic sheet for at least two weeks. This should kill the pathogens in the rootlets. Urea is most effective in alkaline soils, when in acidic soils mixed with calcium carbonate (0.2-0.3kg/cubic meter soil) is suggested.
3. If it is not possible to dig up the roots and the affected area has an irrigation system, then waterlogging for a month is an option. This should kill any surviving fungus.
4. There are two chemical treatments which can be applied to healthy trees surrounding an infected area or to trees in the early stages of infection.
(a) Treated soil. Treated soil is made adding the following mixture to one cubic meter (tonne) of soil: 0.4kg (or 0.4L) of tridemorph (Calixin) or triadimefon (Bayleton) or flusilazole (Nustar); 0.4kg (or 0.4L) of oxine copper or oxine copper + copper hydroxide or prochloraz; 2kg of urea; 0.3kg of lime (unnecessary for neutral or alkaline soils). The treated soil is spread around the base of target trees at a thickness of 3-5 centimeters, to a radius that covers the entire crown, if possible. When the soil is spread, it is wetted, and ideally covered with plastic for a month. If the area is prone to waterlogging, the top 3-5 cm of surface soil can be removed before treatment, but be careful not to damage roots during this process. Treatment should be repeated once six months after the initial treatment.
(b) Fungicide injection. A fungicide treatment is made using equal quantities of the following components: tridemorph or triadimefon or flusilazole diluted 500 times; oxine copper or oxine copper + copper hydroxide or prochloraz diluted 500 times; urea diluted 100 times; lime diluted 200 times (unnecessary in neutral or alkaline soils). This treatment is diluted and applied. Ideally it should be injected into the soil under pressure; it can also be sprayed, using 10-15L per square meter. The area of application should be equal to the crown. After spraying the soil should be covered with plastic for a month, and the treatment should be repeated twice, at three months and six months after the initial treatment. If the soil is poor, moderate quantities of fertilizer can be added to improve the trees' resistance.