Accelerated test methods are needed to evaluate the initiation and progression of decay in wood exposed aboveground. The relationship between test conditions and initiation of decay, however, is poorly understood. Southern pine and maple L-joints and lap-joints were exposed aboveground in a configuration that encouraged water entrapment at the Valley View Experimental test site near Madison. Wisconsin, (hazard zone 2, moderate decay hazard). Test units were evaluated over 120 weeks for visible signs of decay by the pick test, immunodiagnostics, and fungal isolation. Maple lap-joints began to show evidence of incipient decay afterjust 2 weeks. Ten out of 15 maple lap-joint specimens were positive for the immunodiagnostic wood decay test after 6 weeks. Seventeen out of 21 fungal isolates cultured between 12 weeks and 16 weeks were identified as Irpex lacteus, a common white-rot basidiomycete which was isolated from both pine and maple specimens. Maple lap-joints were the first specimens to show visible signs of decay (68 weeks), followed by maple L-joints. pine lap-joints, and pine L-joints. Moisture content of the joint area of shaded specimens was not directly related to rainfall and covering specimens inhibited wetting, thus the onset of decay was delayed. We concluded that under shaded conditions in a moderate decay hazard zone: 1) immunodiagnostic tests were a rapid indicator of incipient decay, 2) decay was detected in lap-joints earlier than L-joints, 3) decay was detected in maple specimens before pine specimens, 4) Irpex lacteus was the predominant basidiomycete cultured from test specimens. and 5) moisture accumulation in joints under shaded conditions was not related to measured rainfall.
Clausen, Carol A.; Highley, Terry L.; Lindner, Daniel L. 2006. Early detection and progression of decay in L-joints and lap-joints in a moderate decay hazard zone. Forest products journal. Vol. 56, nos. 11/12 (Nov./Dec. 2006): pages 100-106.