Introduced Tree Diseases and Insects 



449 



gether are deadly, even though either 

 alone is of little importance. An exam- 

 ple is the partnership of a fungus, Nec- 

 tria sp., and an imported European 

 scale on beech. The fungus, which en- 

 ters through the scale injuries, is a 

 killer. The partnership has already 

 caused the death of much of the beech 

 growth in eastern Canada and Maine. 

 The partners are increasing in the 

 other New England States and threaten 

 widely distributed beech growth else- 

 where unless climatic factors limit their 

 spread. 



HUNDREDS OF DISEASES and insects 

 that have not yet been introduced are 

 known in foreign countries to attack 

 oaks, poplars, and other tree genera 

 that also grow here. In addition, there 

 undoubtedly are in the various parts of 

 the world numerous undescribed dis- 

 eases and insects that could attack our 

 trees if they gained entrance. 



Asia is the principal source of dan- 

 ger, because many kinds of trees native 

 to that continent also grow here. Fur- 

 thermore, those species have had little 

 or no pathological study. Insect and 

 disease parasites from Europe consti- 

 tute the second threat, even though its 

 flora is less varied than that of Asia. 

 It is not wise to ignore the possibility 

 that other Old World strains of para- 

 sites may be introduced and prove 

 more virulent than the strains already 

 here. 



Despite our inspection service, accel- 

 erated travel gives parasites a better 

 chance than ever before to reach this 

 country in a living condition. 



Airplane traffic alone offers a prob- 

 lem. During the year that ended July 1, 

 1948, officials of the Division of For- 

 eign Plant Quarantines listed the ar- 

 rival of 57,756 airplanes at 47 ports of 

 entry. Planes from as far away as Cairo, 

 Egypt, regularly arrive in Chicago as 

 the first port of entry. Airplane traffic 

 is still increasing. When usual ports of 

 entry are closed because of unfavorable 

 weather, commercial and private air- 

 planes may land where there are 

 insufficient inspection services. Illegal 



flights are not inspected at all. New 

 areas of the world are being rapidly 

 opened up by airplane travel. In 1948, 

 prohibited material was found on 26 

 percent of the planes, and 3,500 inter- 

 ceptions of insects and plant diseases 

 were made during that year. 



During the same period, 44,300 in- 

 spections were made of ships arriving 

 at ports in the United States and in 

 24 percent of the inspections prohibited 

 materials were found. A special survey 

 during 1943-45 for insect pests and 

 plant diseases near ports of entry re- 

 vealed at least 41 insects and 17 plant 

 pathogens that had never before been 

 recorded from the United States. 



The relatively few examples of in- 

 troduced pests here reported, and many 

 unlisted ones, have caused enormous 

 losses to our trees. A more critical situa- 

 tion will arise as more and more pests 

 enter. Once established, they are with 

 us for an indefinite time, each cutting 

 down our forest production. 



Usually the best practice is to plant 

 tree species that originally grew on the 

 area, but additional pests may force a 

 change to resistant tree strains or dif- 

 ferent species. The length of time a 

 tree must grow in place before it is 

 ready for harvest is a serious factor 

 in combatting introduced pests. An 

 agronomist, troubled by a new disease 

 one year, plants a resistant variety or 

 another kind of crop plant the next 

 year. Foresters often have to wait a 

 hundred years, until the trees mature, 

 before they can change the tree crop 

 to another kind. Such factors empha- 

 size the vital importance of preventing 

 new pests from becoming established. 



IN REDUCING FURTHER INTRODUC- 

 TIONS of pests, of first importance is a 

 stricter regulation of the importation 

 of seeds, cions, and plants. Seeds are 

 by far the least dangerous form in 

 which to make new introductions, as 

 clean seeds after surface treatment and 

 fumigation carry very few disease-pro- 

 ducing organisms and insects. Because 

 cions and plants cannot be satisfac- 

 torily inspected for virus and some 



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