Physiological Needle Blight, 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 102, November 2000.
Incidences of severe defoliation of Pinus radiata have occurred again this spring in some locations. Symptoms can be dramatic and the cause of considerable concern for a time. As with Cyclaneusma the newly flushing foliage will generally be unaffected. In the period prior to the spring flush the affected trees may appear devastated. The symptoms are of a yellow-brown or red-brown discoloration of the crown that may start in the lower part of the tree and will often spread to encompass the entire tree. In the early stages affected green needles often have one or more bands of khaki-coloured or red-brown tissue. In other cases the whole needle discolours evenly. Following discoloration the needles droop, and are then cast. Black fungal fruiting bodies can often be seen on the collapsed tissue. Trees under the age of 5 are largely unaffected and the worst defoliation occurs on trees over the age of 15. Complete defoliation has occurred in some trees over 25-years-old. These symptoms have usually been preceded by unusually high rainfall over a prolonged period, and unseasonably warm temperatures. Experience has shown that once rainfall returns to more normal patterns, although there will be a year or two of 'thin-crowned' trees, recovery of the tree crowns will occur. Several fungi are associated with the disorder with Strasseria geniculata and Strasseria sp. often predominant. Other common fungi are Lophodermium conigenum, L. pinastri, Ceuthospora sp, Phomopsis strobi and Pestalotiopsis funerea. All of these fungi are commonly found on pine litter and are associated with the breakdown of senescent or dead tissue. However, some are also weak pathogens when environmental conditions cause stress to the host.
(Margaret Dick, Forest Research)
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