Farm Forestry New Zealand

PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

Defoliation of Pinus radiata

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Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.

From Forest Health News 78, September 1998.

Late winter and early spring of 1998 has brought reports of serious defoliation of Pinus radiata from a number of the Forest Health Advisers. The older the trees the worse the defoliation has been, with some 24-year-old trees losing all of their needles. Symptoms are of a red-brown discolouration of the crown which, although it may start in the lower part of the tree will often rapidly spread to encompass the entire tree. A close examination of affected needles in the early stages of breakdown reveals one or more bands of khaki-coloured or red-brown collapsing tissue which may be at any point along the length of the needle. Black fungal fruiting bodies develop on these bands and total needle collapse rapidly follows. Defoliation of the type recorded this year in parts of Westland, Northland, Taranaki and some central North Island stands has previously been reported in other locations, in the most recent past in some Northland forests. The area attracting the most attention this year, because it is on State Highway 1 is the Brynderwyn hills in Northland. In every case where this phenomenon has been examined, 'out-of-the-ordinary' rainfall has been experienced over several months prior to the defoliation. Several fungi can be found on the needles, two of them - Strasseria geniculata and Strasseria sp. - are often predominant. Others are Lophodermium conigenum, L. pinastri, Ceuthospora sp. and Pestalotiopsis sp. All of these fungi are commonly found on litter and have a role in the breakdown of senescent or dead tissue. Underlying the infection by these fungi there is always the presence of Cyclaneusma minus which, as has been well-documented in New Zealand, may remain latent for several months before symptom expression and needle-cast occurs. We believe that this is primarily a Cyclaneusma problem but that under these extreme environmental conditions the infected needles become colonised by secondary invaders which overwhelm the primary causal organism. Defoliation occurs at the 'usual' time when symptoms of Cyclaneusma needle-cast become apparent - in spring. Symptoms can be dramatic and the cause of considerable concern. However experience has taught us that once rainfall returns to more normal patterns, although there will be a year or two of 'thin-crowned' trees, recovery of the crown will occur.

(Margaret Dick, Forest Research)

From Forest Health News 79, September 1998.

The defoliation of radiata pine which was described in September (FHNews 78: 2) continues to be a cause for concern in a number of locations. Several forests in Northland, some south of Auckland, areas in the centre of the North Island and Taranaki, and forests in parts of Westland are the worst affected. Young trees (under the age of 5) are largely unaffected by this disorder. Defoliation has been worst on trees over the age of 10 and in some cases individual trees have lost all of their needles. In some locations trees as old as 24 years have been badly hit. In every case where this phenomenon has been examined unusually high rainfall  over  a  prolonged  period,  and unseasonably warm temperatures, have been experienced over several months prior to the defoliation.

Black fungal fruiting bodies can often be seen with the naked eye on the dead and dying needle tissue. Although quite a large range of fungi have been identified from such material the most common are Strasseria geniculata, Strasseria sp.,  Lophodermium conigenum, L. pinastri, Ceuthospora sp., Pestalotiopsis sp. and Phomopsis strobi. These are largely needle decay fungi although when environmental conditions are suitable they may be weakly pathogenic. None are new to New Zealand.

Underlying the infection by these fungi is the presence of Cyclaneusma minus which may remain latent for several months before symptom expression and needle-cast occurs. Most infection by Cyclaneusma occurs in autumn-winter, and mild, wet weather (which is conducive for infection) at this time will ensure a high level of needle-cast in the following spring. Research has clearly demonstrated that infection by Cyclaneusma is followed by invasion by other fungi.  For example Lophodermium usually colonised needles about 2 months after infection by Cyclaneusma . Generally needles do not show symptoms of Cyclaneusma needle-cast for 3-6 months. However under extreme environmental conditions, such as those experienced in many parts of the country last winter, the breakdown of the needles begins earlier than usual. At this time symptoms begin to show as needle banding and the red-brown colour of trees seen from a distance.

We believe that this is primarily a Cyclaneusma problem. Discolouration has occurred at the time when Cyclaneusma needle-cast becomes apparent, in spring, although it has been earlier in the season than usual for many of the affected stands. Symptoms can be dramatic and therefore cause of considerable concern, as has been expressed over the past 10 weeks. The spring flush is now elongating and we expect these new needles to be unaffected by the fungi which have been so apparent over the past 3 months. Experience has taught us that once rainfall returns to more normal patterns, although there will be a year or two of 'thin-crowned' trees, recovery of the crown will occur.

(Margaret Dick, Forest Research)

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