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Introduction
Pachymetra root rot is a sugarcane disease unique to Australian cane fields. The disease is not seen in any other country, or in fields where sugarcane has not been previously grown. The disease greatly reduces root growth and yields in susceptible varieties. Pachymetra root rot is a major disease in many parts of Queensland and New South Wales and it is important that appropriate controls are implemented to minimise losses.

Causal Organism
The disease is caused by fungus-like organism, Pachymetra chaunorhiza.

Symptoms
Affected root systems typically exhibit a soft, flaccid rot of the larger roots, and are much smaller than healthy root systems. The fungus invades individual roots, usually near the root tip, and breaks down the internal root issues. These roots either stop growing, or are completely destroyed. This leads to a poorly developed root system and a loss of stool anchorage, which may give rise to excessive stool tipping. Root reddening may accompany the early stages of Pachymetra infection.

Yield Loss
Yield loss of up to 40 per cent in susceptible varieties have been associated with the disease.

Control
Pachymetra root rot control is based on strategic planting of resistant varieties. Some Australian varieties have good resistance to the disease, and, in the production of new commercail varieties, use is made of resistant parents. All varieties are screened for resistance before release, and highly susceptible varieties are not considered for commercial production in badly affected districts.

Short-term fallows (<12 months) have minimal effect on Pachymetra root rot; exposing soil to direct sunlight also has a minimal effect on Pachymetra. Pachymetra spores are long lasting and can survive for more than five years in the soil. Rotation crops such as soybean do not directly affect Pachymetra but have other beneficial effects on soil health. Nu fungicides are effective against Pachymetra at economical rates.

Soil Tests
A soil asay for Pachymetra root rot, based on counting spores of the fungus in field soil, can be used to detrmine the likely severity of the disease in commercail fields. Survets of Queensland cane fields suggest that the northern district, and some parts of the Herbert, central and Fairymead districts are badly affected. The disease is widespread in northern, Herbert, and central Queensland districts, with limited distribution in Southern Queensland, Burdekin and NSW canegrowing areas.

Soil samples for assay in a standing crop should be taken from 0-25cm depth in the soil profile, within the cane row (not from the inter-row space). Enough samples should be taken to ensure representative results are obtained (for example 8-10 sites within a field). The spore counts in the table below reflect probable disease severity in susceptible varieties, depending on whether soil was collected from a fallow field (cultivated) or a standing crop.

Where counts are medium to high, the growth of more-resistent varieties should be considered. In badly affected districts, it may be preferable to grow only highly resistant varieties every second crop, in rotation with varieties with intermediate resistance.