208 DISEASES OF CULTIVATED PLANTS 



previous year's growth, also older branches if showing the 

 indications of disease described above. This work should 

 be done during the winter. Just when the leaf-buds begin 

 to swell, but before they expand, spray with full strength 

 Bordeaux mixture. Spray again with half-strength Bordeaux 

 mixture when the leaves are quite young, and repeat if the 

 disease shows on the leaves. When the source of disease- 

 infected shoots have once been removed, two sprayings, 

 as indicated above, should be sufficient for the season, 

 keeping an eye on the shoots, and remove diseased ones as 

 they appear. 



The cost of thoroughly overhauling the trees and removing 

 all infected wood in the first instance, must be looked upon 

 as an investment, which will return good interest if thoroughly 

 done. 



Diseased leaves and fruit should be either buried by 

 turning the ground over during the winter, or collected and 

 burned. 



Aderhold, Landw. Jahrb., 1896, p. 875. 

 Aderhold, Centbl.f. Bakt. u. Par., 2, p. 593 (1900). 

 Aderhold, Hedwigia, 36, p. 67 (1897). 

 Goethe, Gartenfl., May 15, 1887. 



Pear scab, caused by Venturia pirina (Aderhold), closely 

 resembles apple scab in general appearance, habit, sequence 

 of development on twigs, leaves, and fruit, also in its 

 botanical features. The fruit when attacked cracks much 

 more frequently than in the case of apples. The disease 

 is most prevalent during a cool, wet season. 



Ascigerous form. Perithecia gregarious, mostly on the 

 under surface of dead leaves that have been lying on the 

 ground throughout the winter, 120-160 /A diam., with or 

 without bristles ; asci 8-spored ; spores yellowish-green, 

 unequally 2-celled, 14-20X5-8 /A. 



Conidial form (Fusicladtum pirinum, Fckl.). Effused, 

 velvety, blackish-olive, conidiophores short, wall thick, 

 outline wavy or knotted ; conidia ovate-fusoid, olive, becom- 

 ing i-septate when old, 28-30 x 7-9 /*. 



Preventive measures to be followed, same as those recom- 

 mended for apple-scab. 



Aderhold, Centbl.f. Bakt. u. Par., 2, p. 593 (1900). 



