Aphanomyces Diagnostics

Symptoms

Roots of plants infected with Aphanomyces euteiches become soft and have a water-soaked, honey-brown, or caramel-coloured appearance.

Infection begins on the lateral roots and then spreads to the main root, stopping where the green stem tissue begins. During the early stages of the disease, plants start to turn pale green and eventually yellow or chlorotic.

As the season progresses and conditions remain favourable, the main root typically becomes infected by other pathogens (Fusarium is the most common) and turns dark brown to black. This results in stunted, yellow plants with black or brown stems at the soil surface, which cannot extract nutrients and water from the soil.

Classic signs of an Aphanomyces infection include poor emergence, stunting, yellowing of leaf tissue, a reduced root system, and decaying and brown discoloured roots.

Nodules are often reduced in number, pale in colour, and grey with no visible pink in the centre, indicating they are not actively fixing nitrogen or may be absent and have not formed on the plant roots.

Aphanomyces infections typically occur in patches throughout the field and may expand if conditions are favourable for oospore production over several growing seasons. The worst symptoms are often found where water flows or accumulates and are usually associated with flooded or waterlogged areas.