TREES AND TIMBER 



439 



vated perithecia, the cluster surrounded by a border of 

 dead tissue. Premature defoliation results. The disease 

 is very abundant in all parts of the United States. In- 

 fected materials should be burned 

 in the fall. 



Powdery mildew, uncinulose. See 

 oak. 



Powdery mildew, phyCactinose. 

 See oak. 



FILBERT. See hazel. 



FIR 



Rust {Aeddium elatinum Alb. & 

 Schw.). — This cluster-cup fungus 

 has been noted in Minnesota.' It 

 produces bushy distortions, "witches' 

 brooms," by causing profuse branch- 

 ing of the affected part of the tree. 

 These abnormal branches soon lose 

 their leaves, and cluster cups are 

 produced upon them. The brooms 

 are perennial and increase in size 

 each year, in some cases largely 

 covering a whole tree with the brooms. In such cases the 

 trees are stunted and may even be killed. Infection may 

 be reduced by destruction of the spore-bearing branches. 



Canker (Dasyscypha resinaria (Ckle. & Phill.) Rehm). — 

 Swollen cankers occur in the stems and branches, even 

 girdUng the main trunk and killing the tree. After the 



' Freeman, E. M., Minn. Plant Dis., p. 277. 



Fig. 192. — Elm leaf-spot. 

 After Heali 



