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Tree Pathogen Survival in Chipped Wood Mulch
Uncomposted wood chips from urban tree removals or wood waste are often used as landscape mulches. Many times trees that are removed are in poor health and contain plant pathogens. Mulch chips are also derived from wood waste in the form of pallets and other packing materials; these wood materials may contain indigeneous as well as exotic plant pathogens.
A study was initiated to determine how long a common fungal plant pathogen, Thyronectria austro-americana, the cause of Thyronectria Canker in honeylocust trees, could survive in uncomposted wood chip mulch under various irrigation regimes.
Cankered wood pieces remained a source of inoculum for 143 weeks after placement around trees in an irrigated landscape. Thyronectria austro-americana recovered from cankered wood pieces after 98-weeks on top of or in mulch layers, did produce cankers on inoculated branches of honeylocust trees.
Placement on the mulch surface or buried in the mulch did affect recovery of the fungus, but the results are inconclusive at this time. Amount of irrigation applied to the mulch did not affect the recovery of the fungus.
The results of this study suggest that infested wood chip mulch can be a source of inoculum for plant pathogens. Infested mulch may allow some fungal pathogens to survive for prolonged periods until environmental conditions and horticultural practices favor infection. Thus, the practice of placing mulch derived from honeylocust trees infected with the T. austro-americana around honeylocust trees in urban landscapes should be avoided.
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