DANGEROUS INTERNATIONAL FOREST TREE DISEASES 37 



application of embargoes where they can be imposed without damage 

 to the forest economy. In the author's opinion, the embargo should 

 always be considered when phytosanitary measures are being devised, 

 and only dismissed on very strong reasons against its use. 



It is outside the scope of this paper to discuss all the quarantine 

 measures which have been imposed by various countries against tree 

 diseases. They have been fully summarized in an F.A.O. publication 

 by Ling ( 1952 and after) . The United States regulations, with a very 

 long list of tree genera and species, and with some restrictions applying 

 only to specified regions, represent a painstaking effort to relate quar- 

 antine measures to the existence and distribution of known diseases. 

 The British regulations, as far as conifers are concerned, provide an 

 example of the widespread embargo designed to protect a group of 

 genera from all pathogens known or unknown from all regions. 



In any case, of course, phytosanitary measures can only postpone 

 the more or less inevitable spread of all diseases to all areas where 

 there are susceptible crops for them to attack. Nevertheless such a 

 postponement may have enormous value in giving time for resistant 

 strains to be discovered or developed, and for control measures to be 

 elaborated. 



The remaining sections of this paper indicate what can be done dur- 

 ing this "period of grace" to ensure that we are equipped to meet the 

 forest pathological problems of the future when transport will be so 

 rapid and so cheap that restrictions on movements of goods will be 

 completely out of place. 



Exploratory Action 



"When we consider tropical forests, it is readily apparent that the 

 area which is relatively unexplored from the disease point of view is 

 very large. For many extensive regions incomplete lists of fungi do 

 exist : but rarely, except in the more highly developed countries, have 

 the listed fungi been evaluated phytopathologically. Thus, we have 

 little idea how much damage they are doing in their native country 

 and no information at all on which to base estimates of their behavior 

 if they were moved to other countries or continents. Obviously, there- 

 fore, there is a great need for what might be called "phytopathologi- 

 cal exploration," not only in many tropical forests, but also in quite 

 large areas in the temperate regions. It is clearly important that such 

 work should be done thoroughly and critically. First, an important 

 disease may exist outside the forest proper on scattered trees or in 

 scrub areas, so that surveys cannot be limited to areas of utilizable 

 forest. Second, diseases may be of slight importance in their country 

 of origin because the native host trees are either resistant, as was the 

 case with Endothia parasitica on Castanea in Asia (Beattie and Dil- 

 ler 1954), or of restricted distribution. 



Clearly it is difficult, and in the case of tropical forests impossible, 

 to assess the risk exactly or to consider general precautionary meas- 

 ures until we have a much more widespread knowledge of tree dis- 

 eases. Unfortunately, while short-term visits such as collecting ex- 

 peditions may provide valuable information on the occurrence of path- 

 ogens, evaluation of these pathogens requires study over a period of 

 time and must therefore await the development of a forest pathologi- 

 cal organization in the region concerned. 



