Physiological needle blight
Symptoms, identifying factors, spread and treatment for Physiological needle blight (PNB).
- In the initial stages, needles have distinct olive or olive-with-black resinous bands.
- In later stages, needles turn red-brown.
- After one year, needles turn grey.
Needles droop and wilt and are not easily removed from branches.
Other identifying factors
- Symptoms develop on foliage that flushed in the previous year.
- The entire tree crown may be affected.
- On affected branches, nearly all foliage shows symptoms.
- Symptoms start between May and November.
- Trees older than 14 years are most affected.
PNB is abundant in parts of the Waikato region and very common in Northland and on the east coast of the North Island.
It is uncommon in the greater Auckland region, Taranaki, the greater Wellington-Wairarapa region and all but the west coast of the South Island.
PNB is known to be absent in the areas surrounding the Abel Tasman National Park.
Phosphite spray may be effective in treating PNB. Research is still being done to work out how much phosphite should be used and how frequently it should be applied.
Scion does not recommend spraying affected trees until at least 35% of the tree's leaves show signs of infection. This percentage can vary – more valuable trees should, in general, be treated more promptly.
Farm Forestry New Zealand has more information on the diagnostic features, including pictures, and disease location.