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Melting-out of Kentucky Bluegrass, a Low Sugar Disease. R. J. Lukens, Plant Pathologist, The Connecticut Agricultural Experiment Station, New Haven, Connecticut 06504. Phytopathology 60:1276-1278. Accepted for publication 30 March 1970. DOI: 10.1094/Phyto-60-1276.

Kentucky bluegrass succumbs to melting-out disease when sugar levels are low in turf tissue. The incidence of disease and the content of leaf sugar were negatively correlated to a highly significant degree in the cases of five varieties of bluegrass. Leaf sugars are lower and disease is more severe in turf mowed at 2.5 cm than when mowed at 5.0 cm. Shading reduces the sugar content in the host, and increases disease. An enrichment of host with sprays of glucose initially reduces disease severity but eventually increases disease by encouraging saprophytic growth of the pathogen in sod. Disease increased when host sugar levels were decreased in four ways: cutting height, shade, sugar supplement, and comparison of varieties. Thus, melting-out is a low sugar disease. Sugars may confer resistance to the host by being synthesized into fungitoxic phenols during invasion by the fungus or by inhibiting the synthesis of macerating enzymes by the pathogen.