34 



5. Fruit Spot (Phyllachora pomigena). This Fruit Spot has '>een 

 quite common on Baldwins. It is recog-nized by sunken brown areas, 

 which do not, however, sink very far into the flesh of the apple. The dis- 

 eased spot has a bitter taste. 



Treatment. Spray with Bordeaux. 



The Powdery Mildew [Podosphcera oxyacauthae). This fungus 

 sometimes injures apple leaves. White patches appear on both surfaces 

 of the young leaves, run together, and form a whi'e felt. Ihere are both 

 summer spores and winter spores, but Lhe disease is not hard to control, 

 as it lives almost entirely on the surface of its host. 



Treatment. Spray with Bordeaux at regular intervals. 



The Apple Rust [Gymno sporangium tnacropus). This rust is pecu- 

 liar in that it requires the red-cedar, as a second host, to complete its 

 development. The so-called "cedar-apples" contain spores which may 

 infect the leaves of apples and cause orange-yellow spots on the upper 

 surface and scurfy bunches on the lower. The spores from the apple 

 leaves in turn infect the red-cedar. 



Treatment. Remove red-cedars if practicable and feasible. 



II. Attacking the Stem, Root, Trunk and Branches. 



Apple Tree Cankers These cankers are irregular, sometimes con- 

 centric, open wounds on the trunk, branches, or twigs. The bark is 

 first destroyed by bruises or by sun-scald, and injurious fungous spores 

 affect an entrance. It has been proved that cankers may be produced by 

 (1) the Bitter Rot fungus, (2) the Black Rot fungus, and (3) the Nectria. 

 The Nectria is not common in Ontario but the first and second species of 

 cankers are too common. 



Treatment. Remove and burn cankers on smaller limbs and twigs, 

 and scrape and coat with tar or paint those on the trunk and larger limbs; 

 protect the trunks of trees subject to sun-scald ; spray for Bitter Rot and 

 Black Rot. 



Crown Gall {Dendrophagus globosus). This slime fungus pro- 

 duces enlargements or galls on the roots near the surface of the g^round. 

 Such galls have ben observed mainly on nursery stock in the United 

 States. The diseat.e has not yet become either dangerous or injurious in 

 Ontario. 



Treatment. Remove affected tree and burn. 



1. Twig, Fire, or Pear-Blight (Bacillus amylovorus). This bacter- 

 ial disease, so destructive to the pear, is also prevalent in apple orchards. 

 The bacterium enters through the blossoms, and perhaps through wounds 

 and insect punctures. As a rule, the terminal flowers, leaves, and twigs 

 are first killed, the diseased parts appearing as if scorched by fire. The 

 bark becomes black or brown, and the inner bark and cambium are des- 

 troyed. The disease travels backward into the branches, so that in time 

 the entire tree may be killed. The injury is most marked in rapidly grow- 

 ing trees. It is believed that bees are the unconscious agents of infection 



