6 Wood Discoloration

8.2 Tree Wounds and Tree Care 173
destruction to the ozone layer. Log fumigation needs an exemption. In Europe,
to monitor that sufficient bromomethane fumigation of the oaks has been carried
out, the TTC test (Brunner and Ruf 2003) is suitable. The test is based on
the fact that the gas kills not only the oak wilt fungus but also the living cells
of oak sapwood. These cells would survive for several months in logs that are
not treated with gas. Increment cores of the whole sapwood are treated with
a 1% solution of 2,3,5-triphenyl-2H-tetrazolium chloride (colorless), which
discolors dark red to triphenylformazan in contact with living cells by their
dehydrogenase activity (Rütze and Liese 1985b).
Fumigation with bromomethane has also been applied to four pathogenic
fungi in larch heartwood (Rhatigan et al. 1998). Due to the pending restrictions
of bromomethane for phytosanitation in general, the potential substitution by
sulfuryl fluoride and iodomethane was investigated (Schmidt et al. 1997c,
Unger et al. 2001).
There are privileges of the import regulations for the fewer endangered white
oak: no fumigation during winter months, however immediate debarking and
burning of the bark as well as immediate wood processing. Since the wood of
both oak groups is hardly or not at all to differentiate by appearance, a color
test is suitable: When sprayed on the heartwood of any species of white oak
a sodium nitrite solution produces a blue-black color within a few minutes,
whereas the color is a reddish brown in red oak (Willeitner et al. 1982).
The possible oak wilt transmission to Europe was discussed several times
in connection with the increasing illness of European oaks (Siwecki and Liese
1991). These damages develop however due to a complex effect of abiotic factors
(dryness and pollutants as predisposing factors, severe winter frost as acute
stressor) and biotic influences (leaf-eating insects, nematodes, phytoplasmas,
and Armillaria spp. as weakness parasites, other Ceratocystis species, other
fungi.) The literature on the role of pathogens in the present oak decline in
Europe has been compiled by Donaubauer (1998).
8.2
Tree Wounds and Tree Care
8.2.1
Wounds and Defense Against Discoloration and Decay
Initiation for discolorations and decay are predominantly wounds that are
frequently caused by animals chewing, branch breaking, pruning, mechanized
wood harvest, construction injury, and motor traffic (Tattar 1978).
Rots in living trees might occur fast or result from processes of many years,
which frequently remain hidden for a long time, until fruit bodies appear, or
the tree is broken, thrown by the wind, or felled.
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