Minnesota Plant Diseases. 361 



Powdery mildew of .apple [Podosphacra Icncotricha (E. ami 

 E.) Salmon]. This mildew attacks apples, pears, thorns and 

 juneberries. It affects chiefly the seedling plants by injuring the 

 leaves. It forms a fine, whitish, powdery mycelium on the sur- 

 face of the leaves. The small black capsules appear in late sum- 

 mer. Summer spores are produced in the manner usual for the 

 powdery mildews. The small, black sac-capsules are produced 

 in late summer. They are provided with appendages, which 

 form a crown on the summit. The appendages are branched 

 several times in a forking manner. The capsules, when broken 

 open, are seen to contain each a single spherical sac. enclosing 

 about eight spores. 



Spray seedlings with bordeaux or ammrmiacal solution of 

 copper carbonate shortly after the buds have opened md at inter- 

 vals of ten to twelve days for two months. 



Powdery mildew of plums and cherries [Podosphacra tridac- 

 tyla (ll'ulf.) DcR y.]. This mildew attacks leaves of plums and 

 cherries. It is f< und chiefly on young plants. It forms a fine 

 mycelium on the surface of the leaves. The small, black fruit- 

 ing-bodies appear in the fall. These sac-spore capsules are nro- 

 vided with appendages which resemble those of the p wdery 

 mildew of apples K:ich capsuk* contains a single sa? with eight 

 sjx>res. 



For preventives see Powdery Mildew of Apple. 



Plum pockets (l^vonscns prnni l-'ckl.). Plum pockets are 

 very familiar objects to all raisers of plum trees. Cherries are 

 also affected by a similar disease. In this disease the fruit is 

 peculiarly enlarged to considerably more than its natural si/e and 

 is at first yellowish, becoming grey as a coat of spores form on 

 the surface. The diseased fruit has no st<'iie. the entire fruit 

 wall being soft. The mycelium j>enneates the tissue "f the 

 pocket and forms spores in sacs on the surface. The mycelium 

 may live over the winter in the twig" <>f the plants, s tint a plant 

 part once infected may produce p >ckets yearly. This yearly pro- 

 duction of pockets does not always take place, but they may a|>- 

 pear only every other year. The disease does not seem to spread 

 with great ease, for it has l>ecn observed that trees neighboring 

 on a diseased one may remain free from pocket*- for a long time. 

 The spore> are borne In elongated sacs which are arranged in 



