I 
THE DANGER OF SPREADING DISEASES 
ON POPLAR CUTTINGS 
55. During my visit to Europe under the auspices of the Organi- 
sation for European Economic Co-operation to investigate chestnut 
blight on European chestnuts and oaks, field observations were 
also made in different countries on diseases on poplars. Poplar 
diseases were discussed with various European pathologists, 
foresters, and growers. In general, there seemed to be a lack of 
appreciation of the destructiveness of the various poplar diseases, 
though, of course, many people recognised the danger and were 
taking precautions to lessen the risk of bringing in new diseases 
on poplar cuttings. The widespread exchange of cuttings from 
country to country, in some cases in large numbers, and parti- 
cularly the shipment of cuttings by the thousands from one continent 
to another, may result in heavy losses from introduced diseases. 
Once a disease becomes widespread in an area, it is usually 
there forever, plaguing future tree breeders and foresters. In some 
areas breeding disease-resistant poplars may soon be as difficult 
as- breeding resistant tomatoes in Florida, where there are nine 
different diseases for which resistance in tomatoes must be com- 
bined. In Europe, the forest tree disease problem is further compli- 
cated by the ease of natural spread of many diseases from country to 
country; therefore the efforts of many countries to keep a particular 
disease from ether continents from becoming established are nulli- 
fied by lack of proper quarantine restrictions in some one country. 
56. Melampsora rusts were noted in European countries on 
plantings from which propagating material was distributed. These 
rusts are widespread around the world, but there are different 
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