Rhabdocline needle cast

Rhabdocline pseudotsugae

Rhabdocline needle cast is a foliar needle disease of Douglas-fir (Pseudotsugae menziesii) caused by the pathogen Rhabdocline pseudotsugae. Christmas tree plantations often suffered the most damage from this disease.

On this page

• Description
• Host tree species
• Damage symptoms
• Management
• Identification images

Description

Rhabdocline infections on the current year's growth appear as yellow, coloured blotches on needles from early spring through to early summer. Disease progression accelerates through the summer with the blotches resulting in reddish-brown fruiting bodies. Spores are released from these fruiting bodies to infect the newly formed needles of the current year's growth.

The infected needles are asymptomatic and remain attached to twigs and branches through the winter. In the spring the cycle repeats to infect the newly forming needles. Spore release is dependent on moisture available through high humidity, dew or rainfall. Once spore release has occurred affected needles are dropped.

Rhabdocline needle cast occurs throughout British Columbia on both interior and coastal varieties of Douglas-fir.

Host tree species

Douglas-fir, especially those in plantation environments.

Damage symptoms

Infection with R. psuedotsugae causes host trees to develop needle discoloration and loss. Repeated heavy infections can lead to the complete defoliation of old foliage of the host tree and a reduction in growth or mortality in small trees. The decrease in visual appeal is a major concern for Christmas tree plantations.

Management

Rhabdocline does not complete its disease cycle in fallen needles or in foliage on cut branches. Therefore sanitation by cutting diseased lower branches and severely affected branches can contribute to disease suppression in plantations.

Cultural control methods used in forest nurseries and Christmas trees plantations, such as minimizing prolonged periods where foliage is wet and providing adequate tree spacing have been shown to reduce disease pressure. However, these methods are not feasible within a forest stand or at the landscape level.

Identification images