Fusarium Blight and Physical, Chemical, and Microbial Properties of Kentucky Bluegrass Sod

Abstract

SMILEY, R. W., M. M. CRAVEN, and J. A. BRUHN. 1980. Fusarium blight and physical, chemical, and microbial properties of Kentucky bluegrass sod. Plant Disease 64:60-62. Kentucky bluegrass (Poa pratensis) may become severely damaged by Fusarium blight. When the disease occurred on a well-established plot, its dependence on the environment, a relationship that is not well understood, was studied. Factor analysis was performed to identify associations between Fusarium blight and the other variables. The disease was positively correlated with the thatch decomposition rate, negatively correlated with the plant growth variables, and not correlated with any microbial group including all species, sections, and composite numbers of Fusarium. Sod pH and Fusarium numbers were associated with thatch decomposition rates. Fusarium blight was least severe when the percentage of Fusarium-infected plant crowns was highest. These results are considered in relation to the possible role of phytotoxic substances that are produced during thatch decomposition and act as incitants of Fusarium blight of Kentucky bluegrass. Fusarium blight of Kentucky bluegrass (Poa pratensis L.), reportedly caused by Fusarium roseum (Lk.) emend. Snyd. & Hans. f. sp. cerealis and by F. tricinctum (Cda.) emend. Snyd. & Hans. f. sp.poae (4), destroys bluegrass stands in several regions of the United States. The disease occurs on seeded bluegrass stands that are usually older than 4 yr but may occur earlier on stands established from sod. Occurrence of Fusarium blight on mature turfgrasses is very dependent upon the environmental conditions (3,20), but these conditions remain poorly defined due to the unpredictable nature of the disease in well-controlled experiments. We investigated the longterm (3 yr) effects of fungicide applications on nontarget microbial activities and soil processes in closely monitored Kentucky bluegrass sod (14-16). Fusarium blight occurred on the plot in 1977 (18), and the disease was unexpectedly controlled by several fungicides that have been ineffective in all 1-yr studies. Several properties of sod also appeared to be associated with the incidence of Fusarium blight. An understanding of the relationships between this disease and certain characteristics of host growth and of sod and microbial numbers may allow more complete characterization of the conditions favoring or causing disease. This is especially important because several fungicides that control the disease in the field are not fungitoxic to the alleged pathogens in vitro (12,17). This investigation was conducted as part of Hatch Project NY(C)153434. Accepted for publication 21 March 1979. 00191-2917/80/000010$03.00/0 01980 American Phytopathological Society This report presents the results of correlative and multivariate analyses performed to identify associations between Fusarium blight of Kentucky bluegrass and certain turfgrass characteristics. Because a significant level of multicollinearity existed among variables, simple correlation coefficients could not be interpreted. Factor analysis was used to identify a set of independent patterns of association among the variables. The results of the factor analysis allowed estimation of partial correlation coefficients that provided a statistical measure of the degree of linear association between Fusarium blight and each of