© 2000 by Institute of Chartered Foresters
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Preventing Heterobasidion annosum from colonizing chemically thinned Sitka spruce stems
1 Belfast, Northern Ireland 2 Belfast, Northern Ireland
Sitka spruce (Picea sitchensis (Bong.) Carr.) stems thinned by wounding and applying glyphosate herbicide were found to be prone to ‘infection’ by Heterobasidion annosum (Fr.) Bref. ‘Infection’ as indicated by emerging basidiocarps 3–5 years after treatment was low but highly variable and increasing. Two trials compared three herbicides, two wounding methods and three wound protectants. After treatment, wounds were sprayed four times with H. annosum conidiospores. In trial 1, herbicides were glyphosate or imazapyr. Protectants were urea or the fungicide (CalirusTM). Stem-sections were cut 12 months after treatment, incubated and percentage area colonized by H. annosum was recorded. Control cuts had a low mean area of colonization (<\#060> 5 per cent), contrasting with herbicide treatments where glyphosate gave 63 per cent, and imazapyr 32 per cent. A protectant spray with urea after herbicide reduced this to 28 and 21 per cent, respectively. Calirus reduced it to 16 and 11 per cent. In trial 2, stem sections were cut after 16 months and had greater mean percentage areas of colonization than in trial 1. Chain-saw cuts with glyphosate treatment had 66 per cent colonization, protection with urea reduced this to 48 per cent, or the fungicide Plant VaxTM to 43 per cent. However applying Plant Vax before herbicide reduced it to only 20 per cent. A plugged drill-hole led to a smaller area of colonization than a cut, with glyphosate alone this was 43 per cent and when plugs were pretreated with Plant Vax it was 26 per cent. Borax dusted into cuts was unsuccessful as a potential arboricide. Glyphosate at 18 per cent v/v (diluted RoundupTM) was a more efficient arboricide than 3 per cent imazapyr (diluted ArsenalTM); on the other hand, glyphosate was associated with more H. annosum. Few stems totally escaped infection except in the borax treatment. In trial 1 comparing disc infection with sporophore production 4.5 years later showed basidiocarps to be poor indicators. Mean percentage area colonized showed many significant treatment differences.