PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Dothistroma
Back to Dothistroma
See also needle diseases of radiata pine
SEASONAL DEVELOPMENT OF DOTHISTROMA PINI
From Forest Health News 143, August 2004
In October 2003, a 2-year study was initiated to determine the
main Dothistroma infection period by monitoring the development
of lesions on pine needles. The aim is to pinpoint the beginning
of the infection period so that fungicide can be applied just before
it starts, thereby ensuring the most effective control. Plots were
established at three sites, one at Tauhara near Taupo, one near
Kinleith, and one at Te Matai on the Mamaku Plateau. Assessments
of overall disease were done at monthly intervals, along with
counts on individual needles of initial lesions (small pale yellow
chlorotic spots that do not have typical red banding or black fruit
bodies), fully developed lesions (those with necrotic red areas),
and fruit bodies (small black raised spots within the red region).
At each site, rainfall and temperature data loggers were installed.
There was little change in the average numbers of lesions per
needle on the 2002 foliage between October and late December
but fruit bodies were seen by November (see diagrams). By early
February, all needles had fallen with the exception of those on
four branches at Te Matai. New branches holding 2003 foliage
were then selected to continue the study and between early
February and early May the number of lesions and fruit bodies
increased significantly. Numbers remained static or decreased from
early May to mid July.
As can be seen from the temperature and rainfall figures for Te
Matai (below), it was particularly wet from late January to early
March and was then dry until mid-May.
The previous summer (2002/03) had been very dry and the
numbers of lesions and fruit bodies appearing on needles during
that season were low. However, spores produced from fruit bodies
on this foliage resulted in visible infection on the 2003 foliage by
early February. High and regular rainfall during late January and
February led to a rapid increase in lesions and fruit bodies, and
spores produced during that period resulted in the lesion
development seen from March to early May. Temperature did not
appear to be a limiting factor until May after which no lesion or
fruiting body development was seen.
More observations are needed but these data suggest that fungicide
should be applied in late October to prevent infection that would
otherwise produce spores initiating secondary infection in
February and another infection cycle in April, if conditions are
suitable.
Thomas Merriman of Vigil carried out the tedious and often
onerous task of counting lesions and fruit bodies on individual
needles — his efforts are very much appreciated.
(Lindsay Bulman, Forest Research)
