Many pine trees have been turning red the past few months as a disease takes its toll after a wet season.
The pine tree disease, red needle cast, was hitting trees particularly in the south of North Island and was appearing in pines north of the South Island.
Many motorists going over the Saddle Rd and Pahiatua track from Manawatū to Hawke’s Bay had seen, and been enquiring about, pine and douglas fir trees severely depleted of needles.
The die-back was mostly because of red needle cast, a Phytophthora infection that liked long periods of wet and humid conditions, such as those experienced this year, said Dr Nari Williams, a senior forest pathologist with the forestry research institution Scion.
“The dieback can cause virtually all the current needles on a tree to be cast off but tree mortality has not been observed and there is needle regeneration with the spring growth flush,” she said.
PHOTO: MARION VAN DIJK/STUFF
Many trees looked bad, but were not killed by the disease.
“As a result the pine trees lose some productivity, through fighting the disease and having to work harder to get nutrients, as well as having to produce extra pine needles.”
She said red needle cast was not the only needle disease to attack pine trees.
“Dothistroma and Cyclaneusma are two other fungal diseases also favoured by humid conditions, and there is a needle blight as well.”
Biosecurity and surveillance expert Brent Rogan said while pine trees had to deal with a few pests and diseases, many were not in New Zealand or were not causing an issue.
Pines were grown because they were a fast growing species and there was infrastructure, such as mills, to deal with the wood from the trees.
Other species were being grown, but there wasn’t the same level of infra-structure to process and market them.
Rogan said red needle cast had appeared on Saddle Rd pines for at least 10 years.
Williams said the disease tended to show up in three year cycles
It took that long for a tree to build up its needle compliment again, but it was dependant on the weather and site as well, she said.
“It is a boom and bust cycle as most needle diseases are dependant on moisture on the needles.”
She said Scion was close to making recommendation for a spray regime to combat the red needle cast disease. Scion through its Healthy Trees, Healthy Future programme is also making strong progress in identifying resistance to disease with some lines in production more vulnerable to needle diseases than others.
“We want to find a prescription for the spray before the next significant cycle of the disease with the mid-term aim for integrated management using genotype selection, site matching and chemical control to manage existing forest assets.
Rogan said commercial forest owners were waiting for the research to catch up, and meantime were on-hold. and not spraying anything to combat the needle cast.
He said “people had gone nuts” alerting the Ministry for Primary Industries and biosecurity teams of the appearance of red needle cast.
Denis Hocking, a Bulls farm forester, said he did not see much disease in his trees.
“But I am on the sand country and it was a natural environment for radiata pine.”
Williams said good air movement and dry conditions could limit diseases.
She said in wet sites resistant radiata pine or alternate species such as redwoods may be an option. Although douglas fir was susceptible to red needle cast there was a lot of variability so New Zealand has a chance to select for resistant douglas fir in addition to radiata pine, but this had yet to be explored.
“In the meantime we are working with colleagues in Oregon and California where it looks like the pathogen originates to try to find out what we can,” Williams said.
Meanwhile, she asked all farm foresters and commercial tree growers to keep their eyes peeled for any new pests or tree diseases.
“People need to be in-tune with the environment around them and the cycles of established pests and diseases and manage their forests accordingly. Keep looking at trees and report anything that seems strange.”