250 EXPERIMENTAL FARMS 



2 GEORGE V., A. 1912 



leaf blight of TEAR and quince (Entomosporium Maculatum, Lev.) 



On the leaves, this disease shows most clearly on the upper surface. It appears 

 as spots, more or less circular in shape, becoming reddish in the centre and with a 

 dark margin. The effect on the leaf will depend on the number of such spots, badi 

 attacks resulting in the yellowing or browning of the leaf and its premature fall. A! 

 disease with which it may possibly be confused is the Leaf Spot, (Septoria Pyricola, 

 Desm). In this latter case, however, the spots are large and more angular and there 

 is not the same difference in appearance between the two surfaces. 



On the fruit a similar spotting is produced, red at first and subsequently darker, 

 often followed by cracking. 



The disease may be controlled by the same spraying treatment as employed for 

 near scab. 



DISEASES OF PLFM AND CHERRY. 



black knot of plum and cherry (Plowrightia Morbosa, [Schw.] Sacc). 



(Plate III. I). 



The striking and unsightly appearance known as 'black knot' is familiar enough 

 to the grower of plums and cherries, and a few remarks as to its origin, nature and 

 manner of growth may not be out of place. It may be found on nearly all varieties 

 of plums and cherries, both wild and cultivated, and it is generally assumed that the 

 forms occurring on these different hosts are due to the action of the same fungus. It 

 is this fact of the disease being, presumably, transmissable from wild to cultivated trees 

 that makes it difficult to control unless the neighbouring wild trees are eradicated. 

 The popular name for this disease is well chosen, since, in its mature condition, it con- 

 sists of a rough, black excrescence on the branches extending often for several inches 

 up and down, but usually not going right around. It affects only the woody parts of 

 the tree. This black mass when fully formed is full of small chambers each containing 

 a number of spore-bearing tubes (asci). These spore cases develop during the winter 

 and the contained spores are scattered during the early part of the year. The new 

 infections appear as swellings which crack the bark and later become covered with a 

 velvety, olive-coloured, spore-bearing layer. The formation of these ' summer ' spores 

 continues to about midsummer, when the change to the black, hard knot begins ta 

 take place. 



Control. 



All knots should be cut out several inches below the apparent limit of the knot, 

 so as to be sure to remove all the mycelium of the fungus which might otherwise start 

 into growth again. This is best done when the leaves are off the trees, but the opera- 

 tion should be completed early in the year, before, say, the first of March. After this 

 a watch should be kept for knots developing during the growing season and they should 

 be removed as soon as noticed. As mentioned above, where the disease is bad, 

 attention should be given, if practicable, to the wild trees in the immediate vicinity. 

 Spraying specially for this pest is hardly profitable, but the usual applications 

 against other diseases will help also as preventives against this. 



