MARKET DISEASES OF FRUITS AND VEGETABLES 43 



surrounded by small, crescent-shaped slits. As the fruit grows, 

 these form corky, russeted scars. In the fall adult curculios of the 

 new generation often feed on the ripening fruit, making shallow 

 pits, mostly around the calyx and stem ends (pi. 15, E). These do 

 not heal over and may permit the entrance of decay organisms. 



CAUSE 



Adult plum curculios are small, hard-shelled beetles with long 

 snouts. They hibernate in trash in orchards or in brushland or 

 wasteland nearby and begin to return to the apple trees about the 

 time these come into bloom. Most of the egg laying and feeding is 

 done during a period of 4 to 6 weeks after petal fall; a limited 

 amount of feeding is done in the fall. Many of the larvae in the 

 fruit are killed by the pressure of the rapidly growing tissue, but 

 enough of them survive in fallen fruit to maintain the infesta- 

 tion. 



CONTROL MEASURES 



Plum curculio may be controlled by thorough spraying. The 

 spray program should follow the recommendations of the local 

 agricultural experiment station. 



(See 101.) 



Powdery Mildew 

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



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

 blossoms, and fruit of apple and pear. On all these parts it shows 

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

 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 fruit either by spore ger- 

 mination 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. 2, D). 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 for the fact that there 

 is always more or less of the lacy russeting around the edges of 

 these larger affected areas. Furthermore, the surface of these 

 affected areas is smooth, not roughened as in spray injury. 



Powdery mildew attacks the fruit of pear more commonly than 

 the foliage or twigs and produces blackened areas, which become 

 hard and may eventually crack open. On pears it is most serious 

 when they are interplanted with susceptible varieties of apple. 



Powdery mildew occurs in nearly all parts of the United States 

 where apples are grown but is usually controlled by the scab 

 sprays applied in eastern orchards. It is generally more of a prob- 

 lem on the Pacific coast than elsewhere. It has been reported as 

 seriously affecting pears of the Flemish, Bartlett, Anjou, and 

 Idaho varieties in Washington and Oregon and is known to occur 



