Monochamus alternatus Hopeis is an important vector of nematode pests of timber in Korea, particularly Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle. Previously, we reported that ethanedinitrile (C₂N₂) has the potential to replace methyl bromide and metam sodium to control M. alternatus larvae and B. xylophilus under low-temperature (<5 °C) conditions. Herein, we report on fumigation trials of C₂N₂ over a 3-yr period (February 2013–October 2015) conducted at higher temperatures. The trials were conducted under 24 different conditions that incorporated varying fumigation chamber types (plastic sheeting-enclosed chambers of differing construction or an ISO shipping container, interior size: 5.90 m length by 2.35 m width by 2.40 m height), log water content (24.1–43.5%), filling ratios (5, 20, and 40%), and temperatures (10.5–17.3 °C). Highest concentration × time (Ct) product values were obtained with the ISO shipping container followed (in order of decreasing Ct values) by a 0.1-mm-thick, low-density polyethylene tarpaulin enclosure, a 0.1-mm-thick polyvinyl chloride (PVC) tarpaulin enclosure, and a 0.05-mm-thick PVC tarpaulin enclosure. The correlation between Ct product value and mortality of M. alternatus larvae was calculated with all treatment combinations. From this, the L(Ct)₅₀ and L(Ct)₉₉ values for C₂N₂ were determined to be 73.19 and 194.90 g h m^–3, respectively. Ethanedinitrile showed promise as a practical alternative fumigant for use on fresh pine logs infested by M. alternatus larvae.