38 MISC. PUBLICATION" 16 8, U.S. DEPT. OF AGRICULTURE 



This is characterized by chocolate-brown, sunken areas of irregular 

 outline varying in diameter from half an inch to 2 inches or more. 

 Scattered over the surface of these areas are depressed circular 

 spots the color of which is a lighter brown than the rotten area 

 surrounding them (pi. 1, F). Under market conditions this late 

 stage of the rot is less likely to show the white fungus threads and 

 pink spore masses than is the first stage. At any stage the rotted 

 areas are rather firm and dry, or at least not watery, and the 

 affected tissues have a bitter taste. 



Pink-mold rot is sometimes confused with fisheye rot, caused by 

 Corticiuin centrifuguvi. The two can generally be distinguished by 

 the fact that on fruit affected with pink-mold rot there is usually 

 a conspicuous white to pinkish growth of the fungus at the center 

 of the affected spot, whereas spots of fisheye rot show very little 

 fungus growth except under conditions of high humidity. Pink 

 mold is a shallow-growing fungus, penetrating the flesh about an 

 eighth of an inch, whereas Corticium grows much deeper and in its 

 late stage extends to the core. 



Below 50° F. pink-mold rot develops very slowly and is not at 

 all likely to start at new places; at 32° it is checked almost entirely. 

 Control is therefore best obtained by means of refrigeration. The 

 rot rarely spreads from one fruit to another unless scab is present 

 and the fruit is held for some time at fairly high temperatures. (^^, 

 ^7,57,58,100,1U,19S.) 



POWDERY MILDEW 



(Podosphaera leucotricha (Ell. and Ev.) Salmon) 



Powdery mildew is a fungus that attacks the foliage, twigs, blos- 

 soms, and fruit of the apple and the pear. On all of these it shows 

 first as small grayish or white feltlike patches of fungus gTowth, 

 which by enlargement may in time entirely cover the part affected. 

 Symptoms that develop later are (1) curling and wrinkling of the 

 leaves, (2) blighting of the blossoms, (3) stunting or killing of the 

 twigs, and (4) stunting and russeting of the fruit. The fungus may 

 become established on the fruit either by spore germination on the 

 fruit surface or by growth down the stem from infected twigs. 



Mildew russeting on the apple fruit, in its commonest form, has a 

 peculiar lacy or netlike appearance which distinguishes it rather 

 definitely from russeting caused by spring frosts or spray mixtures 

 (pi. 3, F). In the more unusual form of solid patches in which it 

 sometimes occurs it might be mistaken for one or the other of the 

 two injuries just named, except that there is always more or less of 

 the lacy russeting around the edges of the larger affected areas. 

 Furthermore, the surface of the affected areas is not roughened as 

 in spray injury but is smooth. 



On the pear, mildew more commonly attacks the fruit than the 

 foliage or twigs, producing blackened areas which become hard and 

 may eventually crack open. On pears it is most serious when they 

 are interplanted with susceptible varieties of apples. 



Powdery mildew is known to occur in nearly all parts of the 

 United States where apples are grown, but is more serious in the 



