Project: 1998-04. Report - CYCLANEUSMA NEEDLE–CAST IN NEW ZEALAND
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Date: 2001 Author: L.S.Bulman & P.D.Gadgil Publication: Report Project reference: 1998-04 This report is available for purchase from: |
Executive summary:
The ascomycetous fungus, Cyclaneusma minus, hasbeen experimentally shown to be able to infect
Pinus radiata plants older than about 3 years of
age (temperature range tested: 10° to 25°C). In
susceptible trees, infection by the fungus leads to
disease, which is characterised by premature casting
of 1–year–old or older needles, mainly in spring but
also, to a lesser degree, in autumn. Cast needles
are usually a mottled yellow–brown in colour.
Apothecia (fruiting bodies) of C. minus are
produced on the needles lying on the forest floor
and the greatest number of apothecia per unit area
were produced in autumn–winter (May to August).
Ascospores of C. minus contained in the apothecia
are forcibly ejected and become airborne after a
period of rain. These airborne ascospores were
trapped throughout the year but were most
numerous during the autumn–winter months.
Current seasonÕs needles were resistant to infection
by the ascospores until they were about 8 to 9
months old and C. minus was first isolated from
these needles in autumn–early winter (May to June).
Most of the infected needles were shed when they
were about a year old. At least two morphologically
distinct types of C. minus were found in the New
Zealand population but whether these
morphological differences reflect differences in
pathogenicity is not yet known.
Aerial surveys of forests throughout New Zealand
showed that severity of the needle–cast was highest
in 11– to 20–year–old stands and lowest in the 1– to
5–year–old and over 25–year–old stands. Northland,
Auckland, Waikato, Bay of Plenty, Taupo,
Gisborne, Dunedin, and Southland biological
regions had a high incidence of the disease. The
disease incidence was very low in Nelson, central
Otago, and Canterbury. In all regions, microsites,
particularly those at high altitudes, also had a high
incidence of disease. The relationship between
disease severity (expressed as percentage of the
green crown showing symptoms of the disease) and
growth was studied by carrying out a complete stem
analysis of 20 pairs of healthy and diseased trees at
age 15 years. The pairs were selected when the trees
were 9 years old and disease severity was recorded
annually. There was a reduction of approximately
60% in average volume increment at an average
disease severity of 80%. Trials, carried out to
establish the relationship between diameter
increment and disease severity in different parts of
the country, showed that an average disease severity
of 60% over 6 years resulted in a 50% loss in
diameter increment. Projections of stand growth to
age 30 for various proportions of diseased trees
(mean disease severity of affected trees: 60%)
predicted a reduction in volume of 10Ð14 m3/ ha
for each 10% increase in the proportion of diseased
trees. For the country as a whole, growth loss of
6.6% per annum for the P.Ê radiata estate aged
between 6 and 20 years was predicted. The
corresponding financial loss was estimated to be
of the order of $51 million per year.
A fungicide screening trial showed that fortnightly
applications of dodine or injection with
carbendazim were able to control the disease. Two
aerial applications of carbendazim a month apart
gave no control, but monthly aerial applications of
dodine for 6 months gave appreciable control. The
cost of such measures was not economically
justifiable. Silvicultural trials showed that stocking
density and pruning had no effect on disease
incidence or severity. Trials carried out to test the
effect of applying five different thinning ratios at
five different crop ages showed that, using
susceptibility to the needle–cast as a main criterion
for tree selection, a delayed first thinning at age 7
or 8, followed by a second thinning at age 10
succeeded in achieving an almost disease–free final
crop stand.
This report is available for purchase from:
Forest Research
Private bag 3020
Rotorua
New Zealand
