IRISH GARDENING 



II 



fi-oiii the bark, of 3 quarter to one inch in width, 

 arcl arranged in crowded rows one above the 

 otlier. In this case the up]>er surface is hairy, 

 but tlie spare-bearing- surface beneath is smooth. 



When young and moist they are purplish in 

 colour and leathery in consistency, but when dry 

 they become dingy in colour and shrivel up. A 

 spell of wet weather causes them to expand again, 

 and each time that they do so they give rise to 

 countless minute spores which spread the disease. 



These fructifications may appear at any time 

 of the year, but they are commonest when the 

 heavy rains which usually occur in autumn make 

 the air and wood wet. 



When the spores of the funyus are liberated they 

 are carried by the wind and may alight on a 

 wound on another tree. There they would ger- 

 minate, and the develojjing mycelium would live 

 Urst of all on the dead wood, but, as has already 

 been explained, it attacks eventually the living 

 wood. The spores however that give rise to the 

 disease need not necessarily come from a tree of 

 the same kind as the tree attacked. Stereum 

 inirpurciini from a silvered laburnum, for instance, 

 may cause Silver Leaf in a jdum, and spores from 

 the' fungus growing as a sapro]5hyte on birch, 

 beech, sycamore or any other forest tree which has 

 died from other causes, n)ay infect another tree in 

 the same manner. The presence, therefore, of 

 this fungus on any dead wood in an orchard may 

 be a source of infection even though no case of 

 Silver Leaf is present. 



The wounds through which the fungus can enter 

 may be quite sm>all. but if a large surface is 

 exposed, such as when a tree has been cut back 

 and regrafted. or a branch has been broken by the 

 wind or the weight of the fruit, the risk of infec- 

 tion is greater. 



EcrjNOMic Importance axd Distribution. 



The effect of this disease on the fruit -bearing 

 ca])acity of a single tree is considerable, but of 

 slow development. Young trees are seldom 

 attacked, and as a rule few silvered i)lum trees of 

 less than five years old are seen. The disease 

 usually ap]iears even in a badly attacked orchard 

 as the trees are cominr^ into full beai'in: ;. As the 

 fungus develoi)S the yield of fruit gradually fails 

 and linally ceases as the branches die. Death 

 may not. however, occur for some time. 



The effect on an orchard taken a,s a whole is 

 more noticeable but irregular. The trees imme- 

 diately adjoining the tree attacked are by no 

 means always the next to show disease, and, the 

 fact that disease does not spread directly to the 

 adjacent trees shows that the fungus does not 

 travel through the roots or the soil to the next 

 tree. An orchard may therefore present a general 

 appearance of being silvered before all the trees 

 are attacked, owing to a nvunber of affected trees 

 being d tted about in an irregular manner, and 

 it is only when a number of trees in a row are cut 

 back for regrafting or other purpose that the 

 disease si)reads in an epidemic manner. 



The Victoria and Czar varieties of iilum are as 

 a rule most liable to attack, but an extensive 

 encpiiry coiKliictid by the Board in the fruit- 

 groA\ ill- <listii(ts (if England failed to discover any 

 special susri|itibility or immunity of any other 

 variety. 



The distribution of this disease through 

 England appears to be extensive, and many 

 seriovis cases are re]iorted from all the chief fruit- 

 growing centres, especially those in which plum 

 trees are common. No district apjiears to be 

 entirely free from it. and as far as can be judged 



it is s|)reading ra])idly. According tt) Pickering 

 the disease first became a serious economic pest 

 during the rainv seasons which were experienced 

 about 1903. 



Methods ov Control. 



Many experiments have been conducted with 

 the object of finding a remedy for Silver I>eaf , but 

 although occasionally local successes have been 

 claimed, no really effective remedy has yet been 

 found. The exi)lanation of the apparent success 

 may be due to the fact that Stereum purpureum 

 was never really present in the affected tree and 

 that the silvering was due to other causes. It has 

 also been shown that some affected trees have 

 recovered without any fungicidal treatment, and 

 even without any treatment at all. Very little 

 reliance can, therefore, be placed on reports of 

 the successful treatment of single trees. 



Plugging affected trees with suljihate of iron has 

 been tried. A hole has been bored into the tree, 

 crystals of sulphate o£ iron have been inserted and 

 the hole closed hermetically. Indecisive results 

 only have been achieved by these means, and the 

 process cannot be recommended. No really satis- 

 factory treatment is at i)resent known, that is to 

 say no treatment which is certain to bring good 

 results without running serious risk of causing 

 damage in other dii'ections. 



The only useful advice that can be given at the 

 present time is that precautions should be taken 

 to prevent the spread of the disease. 



(1.) It must be remember.? d that the fungus 

 does not appear on the bark till the branch or tree 

 attacked has been killed, and that so long as a 

 diseased portion of the tree is capable of bearing 

 leaves, even though they may be wholly silvered, 

 it cannot spread the clisease. As soon as the 

 branch dies the fructifications of Stereum pur- 

 pureum are liable to appear and under favourable 

 conditions spreacl the spores of disease. It is 

 therefore unwise to cut off branches bearing 

 silvered leaves, unless the wound is promptly and 

 effectively closed with a coating of tar. Dead 

 branches should, however, be cut off at once and 

 turned before the fungus has time to develop, 

 and the wcmnd should be closed with tar. 



(2.) It must be remembered that the fungus is 

 to be found considerably further down the branch 

 than the level at which the silvered leaves a])pear. 

 When therefore an affected branch is broken or 

 is cut off for anj^ rea.son the wood should always 

 be cut back to' a point where no brown stain 

 can be found. 



(3. ) Dead wood should never be left lying about 

 in an orchard or garden where silver leaf exists. 

 All such wood should be burned on the spot or 

 sawn u)) and used for firewood immediately. 



(i.) Dead trees should be cut down to the 

 ground, and if for any reason they cannot be 

 grubbed up. the stumip should be charred and 

 well covered over with earth. 



(5.) Suckers should never be taken from 

 silv^ered trees for purposes of propagation. 



(6.) The practice of cutting back silvered trees 

 and regrafting them is inad\isable, and may even 

 be a means of spreading disease. 



(7.) There is a persistent behef that disease is 

 spread to healthy trees by pruning them with a 

 knife that has been used for silvered trees. This 

 belief is probably unfounded, but it is better to 

 seal all such wounds with tar, as the bare surface 

 affords an easy opening for infection. 



(8.) The fvxngus flourishes in damp situations. 

 Anv improvement in the drainage of an affected 

 orchard or garden will probably helj) to prevent 

 the spread of the disease. 



