Wet weather and red needle cast disease

Recent weather conditions have been perfect for the spread of red needle cast. We answer your questions about it here:

What is red needle cast?

Red needle cast (RNC) is a disease that infects pine tree and Douglas-fir needles. Infected needles turn yellow then red and are cast or blown off the trees a few months after symptoms appear.

It is caused by the algae-like organism Phytophthora pluvialis.

Infected trees show symptoms between March and September, usually peaking from July onwards.
P. pluvialis is a native of North America where it affects Douglas-fir.

How does it spread?

Phytophthora pluvialis is carried in airborne water droplets. Wet late summer conditions – mist, cloud and rain – are ideal conditions for the disease to develop.

Why am I seeing red pine trees this (2017) winter?

Wetter than normal conditions around the country have seen RNC appearing in Taranaki, Manawatu, Wellington and other areas where it is not usually seen.

Is it a threat to our plantation forests?

The needle loss caused by RNC affects tree growth and can reduce it by up to 40% if the defoliation is severe. However, as the disease tends to be sporadic and unpredictable; tree growth returns to normal after about three years.

P. pluvialis does not pose a direct threat to New Zealand’s log trade. The spores only affect live foliage and do not contaminate logs.

Is there a treatment?

Preventatively spraying pine plantations with copper in late summer or early autumn may be a way manage RNC. (Copper sprays are already routinely used to control other needle diseases.)

Can you tell me more about Phytophthora?

Phytophthora literally means plant destroyer. Phytophthora species are responsible for serious plant diseases worldwide, such as the potato blight that caused the Irish famine.

There are two other major Phytophthora diseases in New Zealand in addition to red needle cast. One is kauri dieback (caused by Phytophthora agathidicida), a disease that poses a serious threat to our indigenous kauri. The other is crown rot (caused by Phytophthora cactorum), which is responsible for significant ongoing damage and apple tree loss

What is New Zealand doing about Phytophthora diseases?

A collaborative research programme addressing the threat of Phytophthora species to New Zealand was established in 2013. The Healthy Trees, Healthy Future programme involves breeding, management and research approaches to combat Phytophthora diseases. The programme is being led by Scion and runs to 2019.

Contact

Lindsay.bulman@scionresearch.com