Needle cast is a term used to describe fungal diseases that cause trees to shed needles. The symptoms of needle cast first appear on needles as light green to yellow spots, which eventually turn red or brown. Growth of the fungal pathogen from the spots on the needle will cause the death of the entire needle. Tiny black fruiting bodies (spore producing structures) form on the surface of the needles before or after the infected needles are shed.

LOPHODERMIUM NEEDLE CAST OF PINE

Lophodermium seditiosum is a fungal pathogen which causes needle cast of pine. Austrian, red and Scots pine are the most susceptible to this disease.

L. seditiosum fruits on dead, one year old needles on the ground or still on the tree. Elliptical, black fruiting bodies, called apothecia, develop just under the surface of the needle and cause bulges. The apothecia are 0.8 - 1.5mm long and appear grey, unless they are wet, because they are under the surface of the needle. When the apothecia are mature in late summer, they open along a medial longitudinal slit and release sticky ascospores. The ascospores are rain splashed and wind blown to current season needles, on which they germinate and cause infection. Most infections occur during August and September. In late autumn and early spring, yellow spots that become brown with yellow margins, develop on infected needles. As these spots enlarge and merge, the needles turn yellow and then reddish-brown. The browning is usually most conspicuous in April and May. Lower branches are usually the most severely affected, although all branches can be affected. Dead needles usually fall in June and July.

Needle cast of pine caused by L. seditiosum can result in growth loss and tree disfigurement.

CONTROL

Daconil 2787F at 2.4 to 4.8L or Dithane M-45 80WP at 2.5kg per 1000L of water, applied in mid July to early August with additional applications every 3-4 weeks if required, is recommended for control of Lophodermium needle cast in nurseries. As this fungicide has a commercial registration, only tree maintenance companies must apply this chemical control treatment for homeowners.

RHIZOSPHAERA NEEDLE CAST OF SPRUCE

Rhizosphaera kalkhoffii is a fungal pathogen that causes needle cast of spruce. Colorado blue spruce and Engelmann spruce are the most susceptible, and white, black, Serbian and Sitka spruce are also affected. Norway spruce is relatively resistant.

Rhizosphaera kalkhoffii overwinters in infected needles on the tree and on the ground. In spring, and often other times of the year, the fungus produces fruiting bodies called pycnidia, on stalks that grow out of the stomata of infected needles. Mature pycnidia are black spheres less than 0.1mm in diameter. Fungal spores are released from the pycnidia and dispersed by splashing and dripping water from spring to autumn. The spores infect current season needles, or stressed or senescent needles of any age. Spores need a period of at least 48 hours of leaf wetness to infect the spruce needles. Infection usually begins in spring and symptoms arise in late summer. Infected first year needles have yellow mottling and some of these needles may turn brown, or purplish-brown in the case of blue spruce. The majority of infected needles brown during late winter and early spring and are cast during summer and autumn, 12-15 months after the initial infection.

Infections in a tree tend to initially develop on lower branches and progress upwards under favourable conditions over a period of years. Branch dieback can occur after 3 to 4 years of successive defoliation. Needle shed and branch dieback can create "holes" amongst healthy branches.

CONTROL

Nurseries can control Rhizosphaera needle cast by applying Daconil 2787F at 9.5L per 1000L of water in spring when new growth is 1-5cm, with additional applications at 3-4 week intervals. Commercial tree maintenance companies must apply this chemical control treatment for homeowners, as Daconil 2787F has a commercial registration.

REFERENCES

Blanchard, R.O. and T.A. Tattar. 1981. Field and Laboratory Guide to Tree Pathology. Academic Press, London.

Sinclair, W.A., H.H. Lyon and W.T. Johnson. 1987. Diseases of Trees and Shrubs. Cornell University Press, Ithaca, New York.