264 PLANT DISEASES 



to the living healthy tissue. Swab the wound with a solution of 

 corrosive sublimate, 1 :1000, and paint over with a lead paint which 

 is free from turpentine. Slit the callus on the edge from year to 

 year to make it spread faster, and keep dead wood well protected 

 with paint. 



CROWN-GALL (Bacterium tumefaciens] . See under PEACH, p. 276. 



NEW YORK APPLE-TREE CANKER (Sphceropsis malorum}. The 

 fungus causing the disease attacks limbs, causing roughened 

 cankers and often girdling the limb ; attacks leaves, causing a 

 reddish brown leaf-spot, and on the fruit produces a black rot. 

 Abundant on Twenty Ounce. 



Control. Remove and burn old cankers. Clean out and dis- 

 infect small cankers as for collar-rot. Soak old limbs well with 

 spray mixture when spraying for scab. Spraying as for apple scab 

 usually controls black rot of fruit, though in the Ozark region 

 a late spraying may be advisable for leaf-spot. Cultivate 

 thoroughly. 



POWDERY MILDEW (Sphcerotheca leucotricha} . Attacks nursery 

 stock, covering the leaves with a grayish white, powdery mildew. 

 Also on leaves and twigs of new growth in the orchard, often 

 causing the leaves to fall. 



Remedy. Lime-sulfur, 1-40, as applied for scab is a specific. 



RUST (Gymnosporangium macropus). A bright yellow rust appear- 

 ing on the young leaves and fruit. Enfeebles the whole tree and 

 produces one-sided fruits. It is known that one stage in the cycle 

 of the fungus is the cedar apple, which occurs on the red cedar. 

 Apples are always infected from the cedar, never from apple 

 to apple. 



Control. Destroy red cedars in the neighborhood, also wild 



. apples and hawthorns. Spray thoroughly in the spring as for scab. 



SCAB ( Venturia incequalis). Olive green, brownish or blackish 

 scab-like spots on leaves and fruit. Arrests growth, and often 

 causes distortion. In severe cases may make the leaves and 

 young fruit fall. Makes leaves susceptible to spray injury. The 

 fungus is known to be dependent upon weather conditions, as out- 

 lined in the beginning of this chapter. The fungus winters reg- 

 ularly on the dead fallen leaves. In the milder climate of Vir- 

 ginia, the fungus may winter on the twigs. 



