Minnesota Plant Diseases. 



357 



which are small, black cushions formed under the skin of the 

 apple. When the spores are ripe the skin is ruptured, and the 

 spores issue in a long cylindrical gelatinous mass which is some- 

 what spirally twisted. Rainwater dissolves the spores apart, 

 and the latter are washed to other fruits, again causing infec- 

 tion. The winter or sac spores are formed in small black cap- 

 sules which are produced in the 

 cankers on the twigs. These 

 cankers are usually found at 

 the bases of infected fruits. 

 The mycelium and winter 

 spores preserve the fungus 

 through the winter. The my- 

 celium, which produces the 

 winter spores, can apparently 

 live saprophytically. 



Decayed fruit, whether in 

 storage or in the orchard, 

 should be destroyed. Diseased 

 twigs should also be pruned 

 back and destroyed. Spraying 

 with bordeaux mixture begin- 

 ning with a winter spraying, and continued frequently in the 

 growing season, will hold the disease in check. Ammoniacal 

 copper carbonate should be substituted for the bordeaux as the 

 fruit approaches maturity. Potassium sulphide has also been 

 used to advantage. 



Brown rot of apples. See Brown Rot of Plums (this 

 chapter). 



Brown rot of plum [S c ler o tinia fructigena (P.) Schrt.]. This 

 is a very common disease O'f plums and may also attack cherries 

 and apples, though the latter rather rarely. In states where the 

 peach is grown, this fruit suffers most of all from the brown rot. 

 The fungus attacks the fruit at about the beginning of the ripen- 

 ing period, but may also extend to the twigs, leaves and flowers. 

 The attacked portions of the fruit turn brownish, forming brown 

 spots which are soft and rapidly grow in size. On these spots 

 arise the summer spores in small clusters which are arranged in 

 circles in the spot. The spores are formed in chains, like strings 



Fio. 191).— Bitter rot of apple. After Clinton. 



