Experiences after the storms of 1990 showed that Armillaria mellea can spread in wet stored timber independent from irrigation system and quality. Visible infection of the timber can be found as soon as the (second) third year of irrigation. Economical loss due to sapwood rot can occur from the fourth year on.
Initially, Armillaria forms white mycelial fans under fresh bark. Once the bark is dead, the fungus tends to spread by root- or string-like rhizomorphs. These are jacketed black when mature. Decomposition can be limited to bark and wood surfaces over long periods.
The following information is based on research by the department for Forest Use, Forest Research Institute Baden-Wuerttemberg, data collected by the forestry commission Stuttgart after the storms in February 1990 (Vivian and Wiebke), and experiences after the storm Lothar (December 1999):
- Armillaria infection is independent from the irrigation system. It can also occur in well irrigated stacks. There is no significant connection between infections and the quality of irrigation. Nevertheless, improper irrigation will lead to increased infection and considerable deterioration of quality.
- Evaluation of Armillaria infection and possible damage is only feasible when removing the logs from storage. the infection is usually less severe on the first few metres from the stack ends. The fungus spreads quicker inside the stacks than on the outer logs.
- Quantification of deterioration of timber is best done after mechanically debarking the logs. On-site, the logs can be checked using a hatchet (alternatively, use a nail, knife point, or file).
- Deterioration of timber starts from the outside. Further fungus growth will lead to damage of the circumferential sapwood, not the heartwood.
- Surveys by the Forest Research Institute (FVA) in 1993 and 1994 (year 3 and 4 after rolling in timber thrown by Wiebke and Vivian) showed approx. 5 % volume loss (range of dispersion: 1.6 % to 7.1 %). Approx. 27,000 cubic metres were checked stem by stem after debarking in the sawmill.
- Surveys by the forestry commission Stuttgart in 1993 and 1994 (using the FVA’s method) on delivery of central contracts showed 6.25 % volume loss (range of dispersion: 1.6 % to 13 %). Approx. 288,000 cubic metres were checked (also stem by stem after debarking in the sawmill).
- In spring 1993 (after 3 years of storage), sawmills did not complain about the timber being deficient. The results of Armillaria monitoring undertaken in 2002 (after 3 years of storage) on various wet storage sites support this experience.
- Sufficient irrigation during rolling out is very important. Insufficient irrigation is linked to the risk of distinctly increased deterioration of quality within a short time.
So far, no Armillaria infections have been found on irrigated debarked timber. The FRI did not have the capacities to carry out an accompanying survey on wet storage of debarked timber after Lothar. However, exchanging experiences with individual operators and sawmills showed the positive effects of debarking timber before rolling in. In general, such timber did neither show Armillaria infections nor brown stains after three years of storage.
The forest office Oberkochen organised wet storage with high irrigation quality of approx. 20,000 cubic metres debarked softwood logs straight after Lothar had thrown them. The first assessment of representative logs in June 2003 (extrinsic quality rating and cutting of disks from butt end, middle section, and top) showed no Armillaria infection on any of the logs. Findings of the University of Munich were equally positive. It looks like intensively irrigated debarked logs are reliably protected from Armillaria infection.
In Baden-Wurttemberg, damage surveys concerning Armillaria infections should follow the method developed by the FRI for central implementation. The fact that the sapwood rot affects volume recovery, not quality, was included in developing the method. Infections result in diameter and consequently volume loss.
- Groß, M.; Metzler, B. (1995): Auftreten und Ausbreiten von Hallimasch in Beregnungspoltern. FVA, Abteilung AWF – Versuchsbericht Nr. 1995/7.
- Groß, M.; Metzler, B. (1995): Auftreten und Ausbreiten von Hallimasch in Beregnungspoltern. Holz als Roh- und Werkstoff 53 (1995), S. 147 - 153.
- Groß, M.; Metzler, B.; Schumacher, P. (1996): Hallimaschbefall an beregnetem Sturmholz. AFZ/Der Wald 6/1996, S. 329 – 332.
- Schumacher, P.; Grosser, D. (1995): Befall länger beregneten Fichtenstammholzes durch Hallimasch (Armillaria spp.) und sonstige Holzpilze. Holz als Roh und Werkstoff 53 (1995), S. 137 – 145.
Back to the main page of the Forestry Crisis Management Advisor Guide: Overview of the different topic collections
Back to the article overview in the: Storm Topic Collection – Coping with Storm Damaged Timber