Farm Forestry New Zealand
PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Blue Stain and Cattle Grazing
Back to tree decays
Date: July, 2001
Author: M. A. Dick and L. S. Bulman
FHRC Project reference: 2000-02
Full report is available from:
Forest Research
Private bag 3020
Rotorua
New Zealand
Executive summary:
Blue stain in the roots and butts of Pinus radiata in a stand on the Coromandel Peninsula was associated with on-going mortality during the 1980´s. During six years of monitoring the stand, from age 8 to age 14, 7 percent mortality was recorded.
At least four fungi were responsible for the blue stain, three species of Leptographium and Sphaeropsis sapinea, In this stand the Leptographium spp. were more frequently isolated than Sphaeropsis sapinea.
Although physical injury to roots near the soil surface, which was attributed to cattle grazing through the stand, provided an infection court for the blue stain fungi these injuries were not the sole entry point for the fungi.
In pathogenicity tests carried out with Leptographium spp. on P. radiata in the forest, and on young potted plants of P. radiata and P. strobus, none of the fungi demonstrated the ability to behave as an aggressive primary pathogen.
Infection of roots and butts by Sphaeropsis sapinea is known to be associated with stressed and/or injured trees both in New Zealand and overseas.
Healthy, unstressed P. radiata were capable of containing established infections and curtailing further spread through the wood. Heavy soils, such as the clays found in many parts of the Coromandel Peninsula and in Northland, are prone to compaction, waterlogging and poor oxygenation.
Compacted soils with poor oxygenation do not favour vigorous root growth and/or active root defence to invading fungi. Cattle in this stand probably contributed to the soil conditions that resulted in root infection and subsequent slow decline of some trees on this site.
In order to reduce the incidence of butt infection and mortality in Pinus radiata growing on heavy soils that are prone to compaction, the grazing of stock through the stands should probably be avoided.
Full report is available from:
Forest Research
Private bag 3020
Rotorua
New Zealand
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