Pythium root rot

Pythium root rot is most common in high rainfall areas, especially where rainfall is high after sowing. Direct drill is likely to increase the severity of this disease especially if the stubble is retained. Herbicides for grass control can also increase the level of damage.

Pythium root rot causes seedlings to develop poorly, becoming stunted with reduced tillers. The root system becomes stunted with few lateral roots, and has a soft yellow to light brown infected areas especially near the tips. The seedlings may also become rotted and die. Affected plants are pale and lack vigour, they occur throughout the crop but may be more prevalent in wet patches of soil.

Severe infections may require a paddock to be resown, however in less severe infections plants may recover especially where nutrition is adequate, but yield potential may be reduced.

Life cycle

Pythium root rot is caused by a number of different species of the Pythium fungus. The fungi occur in all soils and can survive as thickened survival spores for five years or more in soil or plant debris before germinating, after germination, spores (zoospores) are produced which in wet soils, swim towards host plants. Infection of plants is most common in wet compacted soils which favour movement and infection by the zoospore. Zoospores are produced in large numbers on dying plants, allowing for infection of other plants. The pathogen is dispersed when infected debris is transported to un-infested areas and when the soil moisture is enough to allow the zoospores to swim freely. Later in season the fungus produces over summering thickened survival spores.

Control

• Avoid sowing into cold wet soils, especially if direct drilling and retaining stubble.
• Avoid sowing crops directly after applying grass herbicides.
• Ensure that paddocks have adequate levels of nutrition.
• Avoid deep sowing in wet soils.
• Use above management measures and treat seed with Rancona^® Dimension at 2L/T.