MENACE TO ORCHARDING. 205 



others and is much more destructive. The remedies recommended for it 

 apply equally well to any of the others. 



Illinois canker (Nummularia discreta) is easily recognized, even 

 by a casual observer. It does not require close observation to dis- 

 tinguish dead branches of trees that are killed by this fungus. The 

 flow of sap is cut off and the bark dies. Often a branch is killed 

 in a single season and the leaves and apples cling to the twigs for 

 same tin).e. Often the apples hang on all winter. At the base of the 

 limb and often over its entire length may be seen at first small blister 

 like protuberances. As the disease progresses, the tops of these 

 proturberences become more flattened and more nearly resemble nail 

 heads. If a thin layer is cut away with a knife, irregular spots of tan 

 surrounded by a dark brown or black ring may be seen. These spots 

 vary in size from 1-16 to 1-4 inch and are scattered all over the dis- 

 eased surface in most cases, though sometimes few if any are present. 

 Two kinds of spores are produced from these spots, which spread the 

 disease. The first set of spores are produced in the months of July, 

 August and September. Masses of mycelium form in more or less 

 compact branches called stroma: from these masses slender stalks 

 arise, sometimes singly and simple, sometimes branched, on the 

 ends of which the spores are formed. This is what causes the blister- 

 like appearance of infected bark. The spores are set free by the 

 cracking of the epidermis covering these masses and are carried by 

 the wind from tree to tree, producing canker wherever the spores 

 lodge in wounds, if conditions are favorable. The following season 

 during the months of April, May and June another kind of spores 

 are produced from these same Stromatic masses. Unlike those of 

 the first season they are formed in sacks (asci) each sack containing 

 eight spores. Tne sacks are also enclosed, several together in cases 

 (peritheciaj which are arranged in a layer throughout the irregular 

 masses. Closing the opening of each peritheoium is a plug which pre- 

 vents the escape of the spores, until it has been sloughed off or dis- 

 integrated by the action of the weather or removed by some mechani 

 cal means, such as being cut into, by pruning tools, the rubbing of 

 limbs together, etc. When freed, the spores cause infection the same 

 way as the conidia of the season before. 



Infection may arise through spores lodging either in wounds in 

 the bark, or where branches have been removed in pruning. The 

 cankered trees at the Nebraska Station and many orchards over the 

 state were examined and 80 per cent of the cankers were found sur- 

 rounding wounds caused by poor pruning. The remaining 20 per 

 cent were caused by wounds of various kinds. Pickers in climbing 

 trees for fruit, bruise the bark with their shoes. In cultivating the 

 trees are often injured by single trees and machinery striking the 

 limbs. The injury known as "sun scald" often is an open door for 

 infection. 



It sometimes requires several seasons for the disease to destroy 



