SILVER BLIGHT.

Press, Volume LXVI, Issue 20102, 4 December 1930, Page 16

SILVER BLIGHT.

TO THE EDITOB O* IBS PRESS. Sir, Mr T. D. Lennio is reported as saying that nobody here knows tho cause of silver blight. It is quite pcssiblo that Mr Lennio does not know, but there are others who do know,'"and as a matter of fact I have explained it in The I'kess on at least two or thrca occasions. Mr F. T. Brooks, botanist, of Cambridge, is the world's best authority on the subject. He proved. that stereum purpurcum is the cause of the silver leaf. If Mr T. D. Lennio or any other person sends 2s to the Ministry of Agriculture, London, for sectional volume No. 1 on Fungus Pests, he will learn all about it - One of the chief reasons why there is so much of this disease about Christchurch district is the presence of so .many poplars and willow-trees, two of the chief hosts. If the dead stumps and branches of these trees are examined I have no doubt the fructification of stereum purpureum bracket shapes will be found in abundance. Tho fructifications of stereum purpureum are purple mauve when fresh, with a white woolly margin, but they become -lingy in colour with age. In consistency they are leathery. They are very variable in form, and appear either as flat encrustations up to several inches long covering the under surface of the branches or on tho sides of the trunk, or as bracketshaped projections of Jin to lin in width, and arranged in tiers one above the jther. In this case the upper surfaco is hairy, and the under .surface is smooth. Tho purple colour, however, is the characteristic featuro of young fructificationsWith regard to tho method of spreading, the fungus is propagated by the spores, which are freely distributed bv wind. They germinate readily in moist weather, and the fungu.s gains admission to the trees through wounded surfaces, such as pruning wounds, cracked branches, injured trunks, fissures in the bark. On germination a mycelium is produced which first of all attacks the exposed tissues, but subsequently invades tho woody tissues below the wound. It has been shown that infection by spores cannot take place through the sound bark. Where the roots of two trees overlap, the mycelium from a diseased root may attack a sound root if in actual contact with it. (I have had this happen this season.) If a cut is made down below where the leavea are silvered on a branch, the cross-section will show the dark brown or blackish marking'of the disease. Having done a considerable amount of top-grafting and budding, I have had a number of trees infected, oven though all tho large wounds are protected with coal tar. But X have almost always cured the trees by giving the ground around them, outside the branches, good dressings of sulphate of ammonia, or nitrate of soda. About two dressings cure apple trees, and two or three does plums or apricots. Peaches are the most obstinate, and one peach tree took me three seasons to cure him, but that trio is just as good as tho others again now. If the dressing is applied immediately the leaves are seen to silver it is a much easier job curing them. I have some old, plum trees from m liich I had to cut off largo diseased branches many years aero. I gave the surface of the cuts a good dressing of .tar and put a tin disc over the wound, and they are still good I have four larpe, old plum trees that I have cured that way, always applying the sulphate of ammonia to tho ground about them.—"\ours, etc.,

GEORGE LEE. Tompleton, December 2nd, 1930.