PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Dothistroma on the increase
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See also needle diseases of radiata pine
Dothistroma on the increase
from Forest Health News 124, November 2002
Severe defoliation caused by Dothistroma pini has been
recorded in pine plantations in many parts of the country
this year. Approximately 180,000 ha will be sprayed in the
2002/03 season, compared with about 60,000 ha in 2000/01
and 100,000 ha in 2001/02. Three factors govern infection
– temperature, leaf wetness period, and the amount of
inoculum. The main infection period is from November to
February when temperatures are optimal for disease
development. Regions where Dothistroma needle blight is
currently significant experienced two consecutive wet
summers in 2000/01 and 2001/02, in terms of both total
rainfall and number of rain days. The wet weather coupled
with suitable temperatures and increasing inoculum has
resulted in very high disease levels. Delays to spraying last
year because of the unsettled weather have compounded
the problem. Forest owners are making every effort to
ensure that aerial spraying for the control of Dothistroma is
done on time this season and are no doubt hoping for a dry
summer.
The Dothistroma Control Committee has commissioned an
aerial spray trial to be carried out by Forest Research that
will examine the effect of reducing the amount of spray oil
used in the spray formulation. Spray oil is a significant
component of the spray cost and if quantities used can be
reduced without loss of efficacy considerable savings can
be made. The trial, which will also test some new copper
formulations provided by two manufacturers, will be
carried out in late November.
(Lindsay Bulman, Forest Research)
