Rapid Blight: A New Turfgrass Disease found in the UK
In August 2004, I received a turf sample from a golf course in the UK on which the greens ere showing damage that showed symptoms of both fusarium patch and take-all patch diseases. The fescue/bent/meadowgrass sward had developed patches of watersoaked turf (Fig1) which rapidly became sunken (Fig2) when compared with surrounding turf, but which did not show the typical symptom expression of fusarium patch disease. Similarly, the patches of affected turf became reddish in colour over time, but the appearance was not that of take-all patch.
Initial analysis of the affected plants showed no evidence of either fusarium patch or take-all patch diseases or any other fungal disease known to damage turf in the UK. There were no fungal spores on the affected sward and no evidence of fungal mycelium on or within the affected plants, but the infection was clearly developing quickly on both the bentgrass and the meadowgrass plants (Fig3).
Closer analysis revealed the presence of what can best be described as microscopic rugby ball-shaped structures within the affected tissues (Fig 4). Following lengthy discussions with the researchers at The University of Arizona, it was confirmed that the organism seen in the UK turf was a Labyrinthula species or 'fungus' - a fungus-like organism that exists as individual cells joined together by thread-like slime filaments (Fig5, arrowed). Rapid Blight (initially called Chytrid disease) had been first diagnosed as a turfgrass disease in the US in 1995, but it was only in 2002 that the causal organism was identified as a Labyrinthula sp.
This was the first time that a Labyrinthula species and therefore Rapid Blight disease, had been found in the UK and it has now been published as a New Disease Report in the UK's British Society for Plant Pathology journal, Plant Pathology (see link below).
Rapid Blight is a disease that can develop on various cool-season turfgrasses but is associated only with sites where there are increased salinity levels in the rootzone or the irrigation water. The disease has been seen on Poa spp., Lolium spp. and Agrostis spp.. It is possible for the organism to infect other grasses but they appear to be slightly more tolerant that those named. It starts as slightly chlorotic areas of turf, anywhere between 2cm and 30cm+, which appear generally watersoaked but mottled along individual leaf blades. The disease can spread very rapidly and damage can be severe with infections developing through the entire plant. Disease outbreaks tend to show in spring and autumn during relatively dry periods. So far it has only been found to develop on sites where there are elevated levels of sodium or bicarbonate. It is an organism that thrives under saline conditions.
I am indebted to both the Golf Course Manager for his initial interest in the 'unusual disease' on his greens and his subsequent call to me for assistance and also to Dr Olsen and her team at Uni. Arizona for their support in confirming this identification.