What are runner hyphae?
As we move from spring to summer, numerous turf diseases occur. Many of these maladies need to be diagnosed and often end up in plant disease clinics. 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.
Photograph 1. The yellow arrow is pointing to runner hyphae growing along the outside of the turfgrass root. Ectotrophic runner hyphae is a sign of a root infecting pathogen of turfgrass.
ERI fungi are associated with the patch diseases listed in Table 1. These pathogens infect turfgrass roots through mycelia called ectotrophic runner hyphae. Ectotrophic refers to the production of hyphae external to the root that when thicken is referred to as runner hyphae. Originally, ectotrophic runner hyphae were associated with take-all patch caused by the pathogen Gaeumannomyces graminis var. avenae. Subsequently other turfgrass root pathogens identified show signs of “Gaeumannomyces type” runner hyphae.
Photograph 2. Take-all patch on this newly estalbished creeping bentgrass tee.
ERI runner hyphae association with Gaeumannomyces has led to confusion among turf managers who think the hyphae are specific to one pathogen. Runner hyphae is a sign of the pathogens that cause patch diseases. pathogens that produce ERI hyphae are often difficult to identify. To culture these pathogens for positive species identification is arduous and time consuming. Recent advancements in molecular diagnosis may eventually lead to quicker diagnoses; however, currently the relationship between symptoms, hosts and the signs of ectotrophic runner hyphae provides a good diagnosis of the disease.
Photograph 3. Spring dead spot symptoms on bermudagrass as the turfgrass starts to break dormancy in the spring.
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.
Photograph 4. Necrotic ring spot on a Kentucky bluegrass turf. The symptoms have lingered through the fall.
Subjected to severe environmental stresses, turfgrasses continually develop diseases that are difficult to identify. Plant disease clinics and laboratories are helpful for identifying a problem or confirming your suspicions, especially with these type of root pathogenic diseases.
Photograph 5. Root decline of warm season turfgrasses (Take-all) symptom expression on a recently established Tifeagle bermudagrass green.
Table 1: Turfgrass diseases associated with ectotrophic root-infecting fungi
Disease | Pathogen | Primary Hosts | Control |
Take-all patch | Gaeumannomyces graminis var. avenae | Creeping bentgrass | Banner Maxx® II, Briskway®, Caravan® G, Headway®, Headway G, Heritage®,
Heritage Action™, Heritage G, Heritage TL |
Root decline of warm season turfgrasses (Take-all of warm season turfgrasses) | Gaeumannomyces graminis var. graminis | Bermudagrass, warm season turfgrasses | Briskway |
Summer Patch | Magnaporthe poae | Kentucky bluegrass and Poa annua | Velista®,
Banner Maxx II,
Briskway,
Concert® II, Caravan G, Instrata®, Headway, Headway G, Heritage,
Heritage Action, Heritage G, Heritage TL, Medallion® SC |
Necrotic Ring Spot | Ophiosphaerella korrea | Kentucky bluegrass, Poa annua | Banner Maxx II, Caravan G, Briskway, Headway, Headway G, Heritage,
Heritage Action, Heritage G, Heritage TL |
Dead Spot | Ophiosphaerella agrostis | Creeping bentgrass | Medallion SC, Headway, |
Spring Dead Spot | Ophiosphaerella (Leptosphaeria) narmari | Bermudagrass | Posterity®, Velista, Banner Maxx II, Headway,
Headway G, Heritage,
Heritage Action, Heritage G, Heritage TL
|
Photograph 6. Summer patch on a Kentucky bluegrass turf.
About the author
Dr. Karl Danneberger is a professor of Turfgrass Science at The Ohio State University. Dr. Danneberger's contact information can be found here. You may also follow Dr. Danneberger on Twitter: