Abstract
THE rôle played by insects in the spread of plant diseases is well brought out in the case of thecollarrot of rubber trees (Hevea brasiliensis), recently investigated by Sharpies (Bull. 25, Dept. of Agriculture, Federated Malay States, 1916). The disease is caused by the fungus Ustulina zonata, as Brooks(Bull. 22, F.M.S.) has already shown. Sharpies finds that at the time when the trees in a young rubber plantation are thinned out, at the age of about six or seven years, attacks by boring beetles (Xyleborus par- oaulus) become very common. He shows that these insects easily enter trees the bark of which has been injured by the falling of one tree against another. Attacks by the above-mentioned fungus usually quickly follow the beetles which enter rubber trees, the tracksof the insects being convenient ports of entry for the wound-parasite, U. zonata. At the time of thinning a large amount of suitable food material for the fungus is available in the form of soft rubber wood. Owing to the increased development of the fungus under these conditions in conjunction with the greater prevalence of borer attacks during the same period, it follows that the thinning-out stage is the most dangerous one in the life of a plantation as regards the attacks of this fungus on rubber trees.
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Plant Diseases . Nature 98, 500 (1917). https://doi.org/10.1038/098500a0
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DOI: https://doi.org/10.1038/098500a0