Pyrrhoderma noxium

Pyrrhoderma noxium is a species of plant pathogen. It attacks a wide range of tropical plants, and is the cause of brown root rot disease. It has been described as "an aggressive and destructive pathogen". The pathogen invades roots with contact between roots of a potential host with the substrate on which the fungus is growing.

Infection
P. noxium attacks the roots and lower trunk of trees, causing roots to rot and resulting in dieback (another term for root rot). It causes brown root rot disease, which afflicts over 200 plant species in tropical and subtropical regions. The pathogen can survive in the soil and on dead plant material for more than a decade, and the primary source of infection to other plants and trees is from contact with infected root material to the healthy plant's root.

Treatment
Fungicides Calixin, Bayleton, and Nustar inhibits growth for P. noxium on agar medium, however was not ultimately found to be effective in eradicating the fungus in infested wood. A mixture of ammonia and urea, as well as just volatile ammonia in itself, was found able to kill P. noxium in infested wood. Strains of Trichoderma applied in mulch around infected P. noxium trees started to grow new roots within 6–8 weeks of application, and the mycelium of P. noxium  was eradicated after 8–11 weeks of exposure.

Distribution
P. noxium has been recorded from tropical regions, as well as Japan and Australia, but has not been reported from South America.

Brown root rot
P. noxium causes brown root rot, which is a serious problem in Taiwan and Hong Kong.