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Plant Pathology Circular No. 155, June 1975
Fla. Dept. Agric. & Consumer Services
Division of Plant Industry
W. H. Ridings
Norfolk Island pine (Araucaria heterophylla (Salisb.) Franco), commonly referred to as A. excelsa R. Br., is a popular dark green, pyramidal, evergreen tree Grown from lower central Florida southward (1).
One of the serious disease problems of seedlings and young trees in Florida nurseries is a necrosis of the needles at the tips of the branches. This disease is caused by the fungus Colletotrichum derridis Van Hook (2).
SYMPTOMS: Infection appears initially on young, developing needles as brown necrotic spots which may develop into a complete necrosis of the needles (fig.1). Excessively long periods of foliage wetting are conducive to spore germination and infection. The nature of sporulation by the causal fungus allows infective spores to be distributed both by splashing water and wind.
Branch tips containing infected needles will develop healthy needles under dry conditions which are unfavorable for infection. Older, mature needles appear to be unaffected by this fungus, Thus, alternating favorable and unfavorable conditions for infection may result in trees showing zones of unsightly necrotic needles.
Fig. 1. Young developing needles at branch tips subject to infection by Colletotrichum derates.
Contribution No. 401, Bureau of Plant Pathology, P.O. Box 1269, Gainesville, FL 32602.
Literature Cited
1. Bush, C. S. 1969. Flowers, shrubs, and trees for Florida homes. Fla. Dept. Agr. and Consumer Serv. Bull. 195. 179 p.
2. Ridings, W. H. 1973. Colletotrichum needle necrosis of Norfolk Island pine. Proc. Fla. State Hort. Soc. 86:418-421.