In the dry air of the prairie States the brown rot or fruit rot of the stone fruits is mainly confined to the foreign plums and the peach. It rarely attacks the native varieties of the plum, and the writer has never observed it on the Morello cherries. But in the moister air of the States east of the lakes it is a prevalent and serious trouble of the plum, prune, apricot, peach, and often the cherry. But fortunately it can be largely controlled by the methodic use of the Bordeaux mixture. The first spraying is done before the buds start, using one pound of the copper sulphate dissolved in fifteen gallons of water without adding milk of lime. When the buds are swelling use the ordinary Bordeaux mixture. When the leaves are fully expanded it is best to use a weaker mixture on all the stone fruits to prevent burning of the leaves. Two pounds of sulphate, two pounds of lime, with fifty gallons of water, has given best results.
To prevent the show of lime on the fruit of the plum and peach, the last treatment is given with a solution of ammoniacal carbonate of copper (165. Fungi of the Grape and Small Fruits).
The treatment for the rot is equally effective in controlling the leaf spot or blight which, east of the lakes, often causes the premature dropping of the leaves of the foreign plums, and winter injury to the trees.
The same treatment also is mainly a preventive of what is known as "plum pocket." This is a disease to which some of the native plums are subject, which causes the fruits to assume the form of enlarged hollow bladders or pockets. But in addition the pockets should be picked and burned and also the swellings found on the leaves and twigs. In the rot of the stone fruits it is also a material aid to pick off and burn the dried fruits that hang on the trees after the leaves have fallen.
The black knot of the plum and sour cherry is also controlled by spraying as practised for destroying the rot of the stone fruits, with the addition of shaving off the knots as they appear and applying kerosene to the cut surfaces.