There are 4 main pine needle diseases in New Zealand. Find out what the diseases are and how to recognise and treat them.
Blight in Radiata pine
Blight is a type of plant disease commonly caused by fungi. There are different sorts of fungi that can cause blight, including mildews, rusts and smuts.
If your pine trees look like they may be suffering from blight, check the table to narrow down the likely cause.
Cyclaneusma needle cast
Physiological needle blight
Red needle cast
Dothistroma needle blight
When
September to November
June to November
April to October
All year
Tree age
6 to 20 years
15 years +
Usually 3 years +
Planting to 15 years
Spread
No pattern
Very severe
Small area affected
More than 50% of trees within the affected area
Small to medium-sized area affected
Almost all trees within affected area
Widespread
Almost all trees within affected area
Wide variation between trees
Needles
Yellow
Gold
Brown
Brown
Red-brown
Grey
Olive (with or without black bands)
Yellow
Red
Olive (with or without black bands)
Brown
Grey
Red bands with black spots
Wilt
None
Only at later stages
None
Slight
Retention
Needles detach easily
Needles are retained
Needles detach easily
Needles are retained but die
Cambium & bark
No damage
No lesions
No resin
No damage
No lesions
No resin
No damage
No lesions
Some resin blobs may appear at base of affected trees
No damage
No lesions
No resin
If you're unsure what may be affecting your forest, NZ Farm Forestry has a step-by-step identification guide that may help.
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.
Disease peaks between October and November.
Trees older than 14 years are most affected.
Spread
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.
Treatment
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 doesn't 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.
In initial stages, needles have distinct olive or olive-with-black resinous bands.
In later stages, needles turn yellow then red-brown.
Needles remain rigid but are easily removed from branches.
Other identifying factors
The entire tree crown may be affected.
Symptoms may start anytime between March and September but are rare during summer.
Peak disease occurs from July to September, depending on the region.
Needles are cast or blown off the branch within a few months of symptoms. After the needles are cast, the tree crown appears very thin.
Affects trees of all ages.
Spread
RNC is abundant in parts of the Waikato, Central Plateau and Gisborne regions and is very common in Northland, the upper South Island and the Bay of Plenty.
It is uncommon in the greater Auckland region, Taranaki, the greater Wellington-Wairarapa region, Hawkes Bay and the area surrounding Abel Tasman National Park.
PNB is known to be absent in most of the South Island.
Treatment
Phosphite spray may be effective in treating RNC. Research is still being done to work out how much phosphite should be used and how frequently it should be applied.
Scion doesn't 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.
turn red-brown - there is a clear distinction between the red zone and the remainder of the needle
remain rigid, and are not easily removed from branch
remain on the tree after they have died.
The lower half of the crown is usually affected. In severe cases, the entire crown can turn red-brown.
Other identifying factors
Symptoms start on the new flush of needles around December or January.
Disease development continues through to winter – when it slows but doesn't stop.
Peak disease occurs about September.
Affects pines from planting age up to about 15 years.
Spread
DNB is abundant in parts of the Waikato and Central Plateau regions and is very common in the Bay of Plenty and upper South Island.
It is uncommon in the greater Auckland region, Taranaki, the greater Wellington-Wairarapa region, Hawkes Bay and the area surrounding Abel Tasman National Park.
No areas in New Zealand are known to be free of DNB.
Treatment
Plan your copper fungicide spraying for early summer for any trees with less than 15% of the crown affected (at the time of assessment during winter).
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