454 INSECTS AFFECTING VEGETATION 



prevent the germination of the spores. This can be done by spraying 

 the trees with double strength Bordeaux mixture about the first of 

 November to kill the spores on the bark. Under ordinary weather 

 conditions there will be sufficient spray on the bark to kill spores that 

 may lodge on it for a short period of time if the work has been done 

 properly. To catch the spores that are distributed later in the season 

 spray a second time with double strength Bordeaux mixture making 

 the application thorough so that the entire tree is covered with the 

 spray. The second spraying should be done two or three weeks after 

 the first. In rainy weather three or more sprayings may be necessary 

 to keep the bark protected. (Wash. E. S. B.) 



Illinois Apple Canker. The canker-wounds are usually formed 

 on the large limbs near the trunk of the tree. From here they extend 

 upwards on the limb and frequently down into the trunk. The larger 

 limbs may be attacked higher up in the tree, however. The exact 

 position of the w r ound depends on the source and manner of infec- 

 tion. (111. B. 70.) 



The appearance of the canker varies greatly with age. At first 

 the canker spots are inconspicuous so that they would easily be over- 

 looked by the casual observer. In the earliest stages observed the dis- 

 eased bark has an unhealthy, dirty brown appearance. It is usually 

 depressed a little below the living bark. The spots vary in size, being 

 sometimes six inches in diameter at this stage. They grow most rap- 

 idly in the direction of the long axis of the limb. If the interior of 

 the bark be examined it will be found to have a mottled appearance, 

 due to the interspersion of sound areas bark and portions of the wood 

 laid bare. The dead bark clings tenaciously to the decaying wood. 

 This canker is very common in Illinois. The fungus attacks nearly 

 all parts of the tree from the trunk to the youngest twigs. The bark 

 on the diseased limbs at first assumes a dingy brown color and is 

 closely appressed to the wood. It may remain in this condition for a 

 long time, sometimes until the canker spot is nearly a foot in length. 

 Around the margin of the spot the diseased bark is slightly depressed 

 and is separated from the sound bark by a distinct line and often by 

 a narrow crack. Cracks and rifts appear later over the diseased sur- 

 face and the bark assumes the dark charred appearance characteristic 

 of the canker. 



From the nature of the attacks of Nummularia discreta there 

 seems to be no method of curing the injury after the parasite has 

 once gained entrance into the limb. The mycelium extends through 

 the wood some distance beyond the injured spot. It is thus well pro- 

 tected within the heart-wood of the tree. If the canker is found in 

 its first stages, however, it may be useful to cut away the injured 

 bark and a portion of the wood and keep the wound covered with 

 Bordeaux mixture or paint. The bark at the edges of the wound will 

 grow out and heal over the injury. Limbs which have extended dis- 

 eased areas should be removed and burned. When a limb is badly 

 injured it is so weakened that the fruit borne on it is of little value 

 and the death of the limb is only a question of time. Meanwhile 

 every diseased spot is a source o/ danger to the orchard and cannot be 



