A Stew of Pathogens

By Mario Lanthier, CropHealth Advising & Research

The “Manual of Integrated Pest Management for Turf Managers in BC”, published in 2019, is being reviewed to add new materials. As part of the effort, a number of golf courses were visited in late summer [of 2025] to document brown patch, yellow patch and other summer patch and ring diseases present in British Columbia.

To our surprise, we found Pythium at concerning levels in 40% of samples and Leptosphaeria (necrotic ring spot) at concerning levels in 20% of the samples. Pythium was found on roots of turf that appeared healthy. 

On this fairway, the dead areas are associated with annual blue grass. The darker green is Kentucky blue grass. Bentgrass also does not appear to be affected.  The lab report indicates necrotic ring spot, but also a high level of Pythium and a high level of Fusarium (the true Fusarium causing root rot, not to be confused with snow mould).

On this fairway are large areas of dying grasses in a diffuse pattern. The site has excessive thatch.  The lab report indicates a high level of Pythium, a pathogen often associated with excess thatch and water. There is also a high level of Fusarium and a moderate level of necrotic ring spot.

On this fairway is a ring of dead turf, somewhat circular shape.  The lab report indicates a high level of Pythium and a high level of anthracnose.

On this green are patches of somewhat circular shape, light yellow colour.  The lab report indicates a moderate level of Pythium but also Microdochium bolleyi, a different species of Microdochium that causes anthracnose-like symptoms.

Identification of turf diseases is getting more complicated. Recent advances in molecular biology is giving us much detailed information. It is common to find different pathogens within a patch of diseased turf. 

Using visual symptoms remains a quick and effective method for persons with prior experience. In some cases, the pathogen is present but will cause damage only after the plant is weakened by other stresses. With closer examination, a number of pathogens are likely to be found rather than a single pathogen. These other pathogens likely contribute to the deterioration of the diseased turf.

In some situations, various pathogens will infect the turf in a sequence. The primary pathogen colonizes plant parts to feed on sugars and carbohydrates while the secondary pathogen will be a cellulose-decomposing fungi. Secondary pathogens often recovered on diseased turf include Pythium and Fusarium (the real Fusarium causing root and stem rot), as well as the agents causing necrotic ring spot (Leptosphaeria korrae) and leaf spots (Bipolaris and Curvularia).