648 Bulletin 81. 



New Jersey, New York, and Ohio.* California possesses laws 

 aimed to keep all contagious plant diseases out of the state by 

 means of the inspection of all imported stock ; Ontario and Bri- 

 tish Columbia also possess laws designed for the better prevention 

 of certain diseases of plants. If existing laws were enforced the 

 extent of injury from the black knot fungus would be very greatly 

 diminished. Unfortunately the above measures have not in all 

 cases been as eSectual as was hoped, and individual efforts are 

 still required to free a locality from the pest. 



The black-knot fungus may be destroyed while upon the tree, 

 but the operation is tedious. The knots are painted with some 

 liquid which will penetrate their interior, or form a coating over 

 them which excludes the air. As early as 1855 spirits of turpen- 

 tinef was used for this purpose. Kerosene was used in the same 

 manner ten or fifteen years later, and linseed oil has been tried 

 with apparent success. Kerosene and turpentine must be used 

 with caution, for if a heavy application is made the branch be- 

 yond the diseased point will be destroyed and I have seen young 

 plum trees killed outright by a too free use of kerosene. I^inseed 

 oil can be used with safety. It is advisable to use some coloring 

 matter, as the red oxide of iron or white lead, to show what parts 

 have been well covered. But the best way of disposing of the 

 knots is to cut them out and burn them. 



Since the discovery of the fungicidal properties of some of the 

 copper compounds the remedies which are effective in controlling 

 other fungous diseases have, to a limited extent, been recom- 

 mended for the prevention of black knot. Very few, however, 

 seem to have tried the experiment. The only recorded case which 

 I have found is that of Maynard.^ Certain plum trees were 

 sprayed April 19 with a solution made by dissolving one pound 

 of copper sulphate in twenty-two gallons of water. May 19 the 

 application was repeated, but Paris green was added at the rate of 

 one pound to five hundred gallons of the .solution. This injured 

 the foliage severely, so the Bordeaux mixture was used for later 

 treatments which were made May 21 and 29, June 7 and 17, July 



* A copy of the New York law may be found on page 392, Bulletin 7s of 

 this station. 

 t The Country Geiitleman, 1855, P- 106. 

 JMass. Hatch Agric. Kxp. Sta. Bull. 11, Jan. 1891, p. 19, 



