DANGEROUS INTERNATIONAL FOREST TREE DISEASES 121 



tree diseases. Such research may best be done in nature at a location 

 where the pathogen is active. 



(b) Alternate hosts. Especially with the rusts (e.g.. white pine 

 blister rust has one critical stage on currants and gooseberries) the 

 various plants necessary for the development of certain stages of the 

 fungus need to be characterized with precision. 



(c) Environmental influences. Temperature, moisture, light, and 

 mineral nutrition have important influences favoring or discouraging 

 epidemics. The study of microclimate is essential for knowing how 



• the pathogens work and how their damage may be prevented. 



(d) Disseminating agents. The potentialities of different carriers 

 of pathogens need investigation, especially insect vectors. 



(e) Seemingly innocuous pathogen*. Attempts should be made to 

 disclose dangerous pathogens that are seemingly unimportant in their 



. native country. Chestnut blight was considered of no consequence in 

 east Asia, but when the pathogen reached America, it practically 

 eliminated the American chestnuts. 



Suitable experimental plantings might disclose such wolves-in- 

 sheep's-elothing. (The technique for such research might follow the 

 work done with the world collection of wheat). 



(f) Improved methods for eradication. If a dangerous disease 

 should appear in a limited area of a country, eradication might be 

 tried. Fire and chemicals have been useful, but certain other proce- 

 dures also may be valuable. To be most effective, a technique for 

 eradication should be developed in the country where the disease is 

 active. The results should be available for immediate use to coun- 

 tries where the disease might appear as a new invader. 



(g) Disease resistance. In many countries native trees fail to meet 

 the needs for reforestation or afforestation. Trees from other coun- 

 tries have been widely and advantageously used, but sometimes with 

 disastrous results from disease. Furthermore, tree breeders are con- 

 tinually developing improved trees. In both cases tests for resistance 

 to dangerous diseases are essential. The selection and development of 

 disease resistant trees hold great promise. 



For many kinds of research involving pathogens and isolation, sev- 

 eral locations are needed. An island with a mountain might provide 

 many desirable conditions. Changes in moisture occur from the rainy 

 to the dry side. Changes in temperature appear at higher or lower 

 elevations. In some mountain valleys the length-of-day would be 

 shortened. In such isolated places pathogens might be studied effec- 

 tively with little danger of spreading the diseases. 



Relations with Agricultural Research Stations. — In many coun- 

 tries the forest pathologist works in relative isolation from men 

 trained and experienced in handling various field, forage, fruit, fiber, 

 and plantation-crop diseases. Such men usually have a background 

 of information and "know-how'' as well as equipment that the forest 

 pathologist could use with advantage. For the most pan, all this 

 would be available merely for the asking. Active cooperation be- 

 tween forest pathologists and agricultural pathologists deserves not 

 only encouragement but also the active removal of "any physical and 

 administrative barriers that prevent their working together. 



In conclusion, the possibilities are dismaying that internationally 

 dangerous tree diseases may move from one country to another and 

 upset sustained yields. However, international understanding, co- 



