A survey of pine needle blight in radiata pine plantations in north-eastern Victoria: October 1989.  I. W. Smith.  November 1989.  6pp. (unpubl.)

SUMMARY

Reports of an increase in pine needle blight (PNB, Dothistroma septospora) of radiata pine (Pinus radiata) in plantations in north-eastern Victoria led to a survey being commissioned to provide an overview of the distribution and severity of the disease in plantations north of the Great Dividing Range and east of the Hume Highway.

The survey was carried out in October 1989 and was confined to State-owned plantations under twenty years of age, as PNB resistance is generally expressed in radiata pine at ages above 15 to 20 years. The survey team endeavoured to assess each plantation on a compartment basis. Inspection points in each stand were based on topographic features so as to give a range of possible infection intensities.

The intensity of needle-blight was assessed by estimating the percentage of visible crown infection on a scale of 0-6 using only the unsuppressed part of the crown. Spot examinations were used to confirm the presence of D. septospora on the needles. Aerial photographs where available were used to confirm the extent of disease in areas where needle-blight was severe.

Ponderosa pine (Pinus ponderosa), which is very susceptible to disease through all age classes, was used, where present in a plantation, as an indicator plant to determine the early introduction of the pathogen.

PNB was found to have extended from plantations in the north-east to those in the Central Highlands at Narbethong, where it was found to have caused severe defoliation in a patch of 40 year-old Ponderosa pine.

In total, 3850 ha of the plantations surveyed were estimated to be affected by PNB to a level greater than 25% crown infection, with 2130 ha having greater than 50% infection. The Wodonga plantations were found to have the greatest area of PNB with 2030 ha (27%) of radiata pine under 20 years of age with greater than 25% crown infection. Of this area, 1200 ha (16%) had greater than 50% crown infection. Most plantations on ex-pasture sites that had reached canopy closure were severely affected by the disease.

In the Wangaratta plantations, 1245 ha of plantation were affected with greater than 25% crown infection, with 870 ha of this area having greater than 50% infection. Approximately 100 ha in the Merriang, Emu and Running Creek blocks were completely defoliated except for expanding shoots of the current years growth.

Infection in the Benalla plantations was confined to Piper, Warrenbayne and Toorour blocks with only 575 ha (13%) showing crown infection levels above 25%. Of this area, 60 ha were above 50% crown infection. The pathogen could not be detected in other plantations although it may have been masked by high levels of defoliation due to Spring Yellow.

PNB was not detected in the Alexandra plantations with the exception of a ponderosa pine plantation at Narbethong.