DANGEROUS FOREST DISEASES IN NORTH 



AMERICA 



Introduction 



The North American report on native pathogens considered of po- 

 tential danger to other countries has received the attention of the un- 

 dersigned subcommittee of the IUFRO Working Group on Interna- 

 tional Cooperation in Forest Disease Research. Twenty-five forest 

 tree diseases of serious incidence in North America were chosen for 

 presentation at this Congress. 



The subcommittee gratefully acknowledges the excellent cooperation 

 of the various authors and the assistance of many colleagues in the 

 United States and Canada who were so helpful in selecting and de- 

 scribing the diseases that are detailed on the pages that follow. 



J. S. Boyce 

 J. R. Hansbrough 

 A. J. Riker 

 V. J. Nordin 



Brooming Disease of Black Locust 



T. J. Grant 



Agricultural Research Service, U.S. Department of Agriculture, 



Orlando, Florida 



Chlorogenus robiniae Holmes. A systemic brooming virus of black 

 locust in the United States. Brooms are found mainly on stump and 

 root sprouts. There exist all degrees of brooming ranging from severe 

 broom through mild broom to apparently healthy plants that are 

 masked carriers of the infectious agent. Clearing of the leaflet veins 

 is associated with early stages of the disease. There is a brooming 

 of the roots as well as of the tops of the diseased plants. In midsummer 

 brooms are usually found on the terminal growth of the leaders. Oc- 

 casionally the brooming of terminal growth is followed by broom 

 growth down the main stem and onto the side branches. Many 

 broomed plants tend to lose their older leaves early. By late summer 

 and early fall the diseased plants may have shed most of their lower 

 leaves and succulent broom growth is very conspicuous. Herbarium 

 specimens indicate that brooming has been present in some areas for 

 more than 80 years. 



Determination of the relative importance of the brooming disease 

 is difficult because of the variable behavior of infected plants, some 

 of which recover from symptoms whereas others die in part or as a 

 whole. The virus can be carried in root cuttings and scion wood; 

 thus intercontinental shipment of this type of propagating material 

 should be avoided. 



Range: United States from southern Pennsylvania to northeast 

 Georgia and west to southwestern Ohio and Tennessee. 

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