Ghost Grass

A disorder or disease of grass caused by bacteria (Acidovorax avenae, and other species) which causes fine, bleached white or yellow coloured, sporadic and irregular length etiolated growth, to appear overnight, especially in golf green situations which are maintained under intensive, stressed, and especially very short (<3.5mm) mown conditions, as well as in the more compact areas of a green, for example, around the green edges and approaches. A decline in turf quality may or may not also occur with this condition. The etiolation looks, in some ways, like the die back that occurs on a grass leaf tip, which has occurred following mowing which is not producing a clean cut to the leaf. A cut of the sward will remove the irregular appearances, particularly in the immediate term.

The regular application of plant growth regulators (PGR), especially those which inhibit gibberellin production, may also be an influencing factor for this condition, although this may also be more influenced by the consistent use of a PGR, without varying the modes of action. This might be contributing to a hormone imbalance, as there appears to be an increase in gibberellins which is creating a type of rebound effect. An analogy can be made with that of consistently using the same mode of action for a fungicide, which initially provides good control to a disease, but over time there is a build-up of resistance to that type of fungicide by the fungi. However, by contrast some types of PGR can also improve drought and shade tolerance, as well as improve sward density and reduce the impact of anthracnose disease.

There will be numerous factors at play here, so it is important for the turf manager to make a well-considered decision for any action to take, but the first consideration will be to reflect on the maintenance practices and potential stresses being put onto the grass plant. Aligning practices to create conditions which promote a strong and healthy sward should eliminate the appearance of this disorder-disease.

(References:
1. Knowles, J (2011) ‘Ghost Grass', Greenkeeper International, June issue, pp24-25, https://archive.lib.msu.edu/tic/bigga/gki/article/2011jul24.pdf, accessed 14th June 2021.
2. Roberts JA, Ritchie DF, Kerns JP. ‘Plant Growth Regulator Effects on Bacterial Etiolation of Creeping Bentgrass Putting Green Turf Caused by Acidovorax avenae'. Plant Dis. 2016 Mar;100(3):577-582. doi: 10.1094/PDIS-04-15-0419-RE. Epub 2016 Jan 18. PMID: 30688596, accessed 14th June 2021)