Techniques for Inducing Summer Patch Symptoms onPoa pratensis

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Abstract
Two techniques were evaluated for use in studies on the ecology and control of turfgrass patch diseases caused by soilborne pathogens. Sod of mature Kentuckey bluegrass produced in field plots was used to determine whether controlled temperatures in growth chambers could be used to manipulate the expression of summer patch symptoms caused by Phialophora graminicola. The pathogen did not induce disease symptoms on sod at 14.degree. C but did so very slowly at 21.degree. C and rapidly at 29.degree. C. Preliminary evidence indicated that the pathogen grew through sods at 21.degree. C but did not kill plants quickly unless the temperature was increased to 29.degree. C. A sod of Kentucky bluegrass was also produced on a mobile cart in controlled-environment chambers, then inoculated with isolates of P. graminicola and Leptosphaeria korrae. Both pathogens formed circular zones of restricted root growth before foliar symptoms were expressed. After an incubation period of 21 wk at 21-24.degree.C, a patch of grass affected by P. graminicola became visible. Symptoms of the summer patch disesae, which became more clear after the temperature was increased to 30.degree. C, included the ring (frogeye) pattern of well-developed or older patches, a sunken-pocket effect, and heat-stress banding of leaves on tillers marginally affected by root rot. This is the 1st report of a patch disease with characteristic field symptoms being produced under semicontrolled conditions on this host. These techniques may be used to increase the efficiency of ecological, etiological, and control studies on patch diseases of turfgrasses. Observations of circular patterns of restricted root growth during the harvest of commercially produced sod could also be used as a quality control measure to reject areas of fields that are otherwise presymptomatic of these diseases.