78 



ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



on needles (Fig. 75). Of the fungi that cause needle rust, Coleo- 

 sporium solidaginis is most important. Goldenrods and asters are 

 alternate hosts of this fungus. Needle rust may cause defoli- 

 ation and stunt young pine trees, but it seldom causes much dam- 

 age on older trees. 



Sooty Mold. — A heavy, sooty, threadlike growth or crust 

 may appear on needles of pine (Fig. 76), fir, and other ever- 

 greens, and on leaves of elm, linden, maple, tulip tree, and other 

 deciduous trees. This growth, made up entirely of fungus mate- 

 rial, may be in isolated patches or it may cover an entire needle or 

 leaf surface. The fungi that cause sooty mold belong to the fam- 

 ily Perisporiaceae. They grow as saprophytes on secretions 

 (honeydew) produced by aphids and scale insects. Although 

 sooty mold appears unsightly, it causes little if any noticeable 

 damage to trees. Control of the insects responsible for the secre- 

 tions will eliminate sooty mold. 



White Pine Blister Rust. — This stem disease, caused by the 

 fungus Cronartium ribicola, is widespread in the north-central. 



Fig. 76. — Sooty mold, which occurs on many kinds of trees, is conspicu- 

 ous because of the black, threadlike growth or crust produced on the sur- 

 face of leaves and twigs, as shown on this pine. This disease seldom 

 causes serious damage. 



