The decay resistance of chlorothalonil in oil was examined in an accelerated field simulator (AFS). Pinus radiata D. Don and Eucalyptus regnans F. Muell. sapwood stakes were treated, placed in soil in the AFS, and monitored over 4.5 years. CCA type C treated stakes were included for comparison. Water and toluene treated control stakes were heavily decayed after 1-2.5 years. Oil treated controls, though moderately decayed, were still serviceable after 4-4.5 years. At each equivalent retention, chlorothalonil performed better than CCA in treated Pinus radiata and Eucalyptus regnans stakes. Pinus radiata stakes treated to 3.6 kg/m³ with CCA were heavily decayed after 4 years, while 3.1 kg chlorothalonil/m³ treated stakes were only lightly decayed. Similary for Eucalyptus regnans, 6.6 kg CCA/m³ treated stakes were heavily decayed after 4 years, while 6.1 kg clorothalonil/m³ treated stakes were lightly decayed. Most of the decay was due to soft rot. When soil in the AFS was 1.5 years old, it had half to three-quarters the number of microbial propagules as could be cultured from fresh soil, that was collected from the same site as the AFS soil was originally taken.

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