Maine; agricui^tural experiment station. 1910. 403 



occurrence in Maine. The fungi* which cause this trouble pass 

 a part of their Hfe upon the apple and related plants and a part 

 upon the red cedar where they cause the abnormal development 

 of small brown knots on the twigs which are known as "cedar 

 apples." In the spring these knots produce thread-like tubes 

 which when wet with rain swell up, become gelatinous, are 

 orange yellow in color, and throw off large quantities of spores. 

 These spores are capable of infecting apple leaves and are pro- 

 duced when the latter are young and most susceptible to infec- 

 tion. 



On the apple leaf there is first a thickening of the tissues in 

 small spots at the points of infection. Later in the season these 

 thickened places become ruptured on the under side and short, 

 thread-like growths project beyond the broken epidermis. 

 Orange-colored spores are formed in these places. It is on the 

 leaves and fruit of the apple that the injuries caused by this rust 

 become of economic importance. Spraying has not been very 

 successful in controlling this disease. Where the rust appears, 

 the removal of red cedars from the neighborhood of apple or- 

 chards is recommended. 



Powdery mildezu. The common name for this trouble comes 

 from the appearance of the affected leaves, which is shown in 

 Fig. 67. The fungus, Podosphaera oxyacanthae (DeC.) De- 

 Bary, grows upon both surfaces of the leaf but does not pene- 

 trate the tissues, except to throw in short feeding branches. 

 During the summer many spores are formed and it is the masses 

 of spores which give the white powdery appearance. The par- 

 asite spreads rapidly by means of these summer spores. Later 

 in the season another stage of the fungus develops on the dis- 

 eased leaves and this is indicated by the presence of small but 

 plainly visible, spherical^ black bodies which are scattered here 

 and there among the white mycelium. Spores are produced in 

 these bodies which carry the fungus over winter. 



On the apple, the chief damage done by this fungus is in its 

 attacks upon nursery stock where it causes considerable loss. 

 Spraying with diluted lime-sulphur should go far toward con- 

 trolling this disease. 



*Apple rust may be produced by Gmynosporangium jiiacrocarpiis Lk., 

 or G. globosum Farl. It is not known which species is responsible for 

 the rust in Maine but probably it is the latter. The red cedar, /»m- 

 perus virginiana L. is the alternate host for both. 



