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FURTHER OUTBREAKS OF PITCH CANKER

Earlier this year the first report of pitch canker on mature Pinus radiata in Tokai plantation in the Western Cape was published in Australian Plant Pathology. The affected trees were between five and nine years of age and symptoms included resinous cankers on the main stems and branches, flagging of branches and shoot tip die-back. On recent field trips to the Eastern Cape, twelve to 15-year-old P. radiata trees in the George area were noticed showing similar symptoms to those observed in Tokai. Similarly, P. greggii (Southern provenance) in the Ugie area also showed typical symptoms of pitch canker. Isolations from these trees, examination of cultures for morphological features and DNA sequence comparisons confirmed the presence of the pitch canker fungus, Fusarium circinatum, on mature trees in these areas.

The origin of the F. circinatum inoculum for the new outbreaks is not known, but insect transmission is suspected because the deodar weevil, Pissodes nemorensis was found at all sites. Research is currently underway to trace the source of these field infections. The majority of the affected compartments were those that had not undergone the prescribed thinning, indicating that the trees were affected by stress. However, detailed surveys and mapping of outbreaks are required to make useful conclusions regarding these worrying field outbreaks of pitch canker. Foresters are urged to monitor trees for symptoms of pitch canker and to report observations to the TPCP immediately.

The occurrence of F. circinatum on mature pine trees is of great concern. Not only does it threaten the productivity of plantations, but it also has implications for seed production in seed orchards. It is well known that the pitch canker pathogen is seed-borne and up until now, South African pine seed that has been screened has been free of F. circinatum. This is presumably because stem and cone infections are needed to result in seed being contaminated. With the first outbreaks of full-blown pitch canker in South Africa it has become more crucial for all forestry companies to prioritize the screening and selection of trees that are tolerant/resistant to infection by this pathogen. This will be the only sure means to avoid dramatic losses in the longer term.

WE URGE ALL FORESTERS AND FARMERS TO PLEASE LET US KNOW IF YOU SEE ANY OF THE SYMPTOMS OF PITCH CANKER.