440 DISEASES OF ECONOMIC PLANTS 



branch is dead the causal fungus fruits in small disks, 

 orange-colored within, about 4-6 mm. wide and high. 



HAZEL 



Black knot {Cryptosporella anumala (Peck) Sacc). — In 

 1892 Halsted noted black knot as destructive to several 

 hundred trees in New Jersey, and in 1893 Humphry^ 

 described the same disease as upon hazel canes in Massa- 

 chusetts. It is characterized by numerous small elliptical, 

 warty emergences upon the bark of the diseased branches. 

 The diseased portions are sunken, owing to the contraction 

 of the inner bark to a mere line. The girdling produced 

 results in death of the affected canes and general injury 

 similar to that produced by plum knot. Affected branches 

 should be cut and burned. 



HORSE-CHESTNUT 



Leaf spot, phyllostictose (Phyllosticta sphceropsidea Ell. & 

 Ev.). —Unsightly spots upon the leaflets and premature 

 defoliation render this the most conspicuous disease of this 

 tree. The brown spots are at first circular, but as they 

 enlarge are limited by the larger ribs, thus becoming nearly 

 rectangular. Pycnidia may be seen with a lens. This is 

 a decided nursery pest. 



Five applications of Bordeaux mixture have much reduced 

 the spotting. 



LINDEN 



Leaf spot, cercosporose (Cercospora microsora Sacc). — 

 Small circular or large irregular dead spots of the leaf 



1 Humphry, J. E., Mass. (Amherst) Agr. Exp. Sta. Rpt. 10, January, 

 1893. 



