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Arboriculture & Urban Forestry Online
Volume 31, Issue 5 — September 2005


Karel A. Jacobs

Abstract: Field transmission of Sphaeropsis tip blight, Botryos-phaeria canker, and Armillaria root rot was evaluated in a 6-year study of 30 saplings each of Austrian pine (Pinus nigra), eastern redbud (Cercis canadensis), and red oak (Quercus rubra) mulched with diseased needles, bark chips, and wood chips collected from mature trees. Half of the saplings were mulched with fresh mulch materials; half with materials first heated to 60C (140F). Sphaeropsis tip blight was the only disease that developed during the study, and pines mulched with heat-treated materials developed significantly fewer (P 0.001) blighted tips than those mulched with fresh materials (6.8% versus 15.1%). Naturally occurring inoculum of S. sapinea and B. ribis were highly tolerant of heat in laboratory tests and remained viable after 6 weeks and 48 h exposure, respectively, to 55C (131F). Armillaria gallica mycelium and rhizomorphs did not withstand temperatures above 35C (95F) and 37C (98.6F), respectively. The heated mulch treatment was associated with a significant (P 0.001) growth boost in redbuds and oaks during the first two growing seasons. Redbuds averaged two times more height and diameter increment than plants mulched with fresh bark and wood chips. Heating diseased mulch to 60C (140F) diminished the threat of tip blight transmission and likely killed all forms of the pathogens.

Keywords: Armillaria gallica; Botryosphaeria ribis; Cercis canadensis; composting; disease transmission; fungi; heat inactivation; pasteurization; Pinus nigra; Quercus rubra; Sphaeropsis sapinea

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