What are ERI Fungi?

Stressful turfgrass conditions lead to numerous maladies, many of which are sent to plant disease clinics to be identified.  One diagnosis that causes confusion is the presence of ectotrophic root-infecting (ERI) fungi.  These fungi are often associated with root rotting diseases that produce patch-like symptoms. 

The pathogens of these diseases infect turfgrass roots through mycelia called ectotrophic runner hyphae.  Ectotrophic refers to fungi that produce on the outside or external to the root and runner hyphae is thickened hyphal strands.  Originally, ectotrophic runner hyphae were associated with take-all patch caused by the pathogen Gaeumannomyces graminis var. avenae.  Eventually, other pathogens that infected roots were identified and found to produce the “Gaeumannomyces type” runner hyphae".

The runner hyphae association with Gaeumannomyces has led to confusion among turf managers who think they have take-all patch.  The problem with the ERI fungi is that they are difficult to identify.  To culture these pathogens for positive species identification is arduous and time consuming.  Most of us can’t wait several weeks or months for a conclusive diagnosis.  Thus the association among symptoms, the host, and the sign of ectotrophic runner hyphae provides a pretty good diagnosis of the problem.

Control of ERI fungal diseases is difficult because root infection normally occurs weeks or months before symptom expression. Once symptoms appear, control is often difficult. With the ERI-causing diseases, preventative measures should be targeted at or just prior to root infection.

Finally, as turfgrasses are maintained under increasing management and environmental stresses, new and ever-increasing turf maladies are becoming more difficult to identify. Plant disease clinics and laboratories are helpful in identify a problem or confirming your suspicions especially with these type of diseases. 

Turfgrass diseases associated with ectotrophic root-infecting fungi.

Disease Pathogen Primary Host
Take-all patch Gaeumannomyces graminis var. avenae Creeping bentgrass
Root decline of warm season turfgrasses Gaeumannomyces graminis var. graminis Bermudagrass, warm season turfgrasses
Summer Patch Magnaporthe poae Kentucky bluegrass, annual bluegrasss
Necrotic Ring Spot Ophiosphaerella korrea Kentucky bluegrass, cool season turfgrasses
Dead Spot Ophiosphaerella agrostis Creeping bentgrass
Spring Dead Spot Ophiosphaerella (Leptosphaeria)  narmari Bermudagrass