448 



Yearbook of Agriculture 1949 



A vicious circle thus has resulted from 

 the relationship between the fungus 

 and the insect. 



The elm beetle unquestionably was 

 introduced through different ports. It 

 and the fungus were present in burl 

 elm logs imported for veneer manu- 

 facture before quarantines prohibited 

 the movement of elm wood into this 

 country. Beetles and larvae have been 

 found in elm wood used in certain 

 types of crates received from Europe. 

 A larger species of beetle, also a carrier 

 of the Dutch elm disease fungus in 

 Europe, has been introduced into this 

 country in burl logs, but apparently it 

 has not been successful in establishing 

 itself here. 



It is practicable to protect valuable 

 trees from the Dutch elm disease where 

 control measures are applied energeti- 

 cally, but losses are heavy in parts of 

 New York, New Jersey, Pennsylvania, 

 and Connecticut, and spot infections 

 are known as far west as Denver. We 

 may expect that these two pests and 

 phloem necrosis, a virus disease, even- 

 tually will kill most of the elm forest 

 growth in the northeastern quarter of 

 the country. 



The death of shade and ornamental 

 elms is even more tragic. It is disheart- 

 ening to all of us to see the large elm 

 trees, so characteristic of New England 

 and New York, decline and die. Some- 

 time in the not too distant future, when 

 the total value of the elms killed and 

 the annual costs of removing dead trees 

 and of spray and other control meas- 

 ures for those still alive are totaled, a 

 loss figure of hundreds of millions of 

 dollars is not unlikely. 



A EUROPEAN-ASIATIC FUNGUS that 

 causes white pine blister rust entered 

 the country some 50 years ago on im- 

 ported white pine seedlings. Although 

 this fungus cannot spread from pine 

 to pine but must first attack an alter- 

 nate host in this case currants and 

 gooseberries it found plenty of the 

 hosts here. Thus it was able to com- 

 plete its life cycle and spread widely. 

 Its dependence on currants and goose- 



berries, however, proved its partial 

 undoing, because spread of the disease 

 can be stopped by removal of the plants 

 within 900 feet of white pine. 



Whitebark pine, a picturesque mem- 

 ber of the white pine group that grows 

 at high altitudes in the West, usually 

 does not have sufficient commercial 

 and esthetic value to justify the cost 

 of removing the numerous wild cur- 

 rants and gooseberries near them. 

 Thus, most of the trees of this species 

 will be killed by the rust and many 

 park and wilderness areas will become 

 less interesting. Several other high-alti- 

 tude species of white pine may be 

 largely killed in the future. 



OTHER INTRODUCED INSECTS dam- 

 age our forest and shade trees. Among 

 them are the brown-tail moth, satin 

 moth, European pine shoot moth, elm 

 leaf beetle, European pine sawfly, and 

 the European spruce sawfly. 



Various other diseases also have 

 been introduced or are suspected of 

 having been introduced. Not all intro- 

 duced diseases become established. 

 The European larch canker, for exam- 

 ple, was introduced into Massachu- 

 setts, but it spread slowly and was 

 successfully eradicated. We do not 

 know how it would act in the main 

 larch stands of this country. 



A canker disease from Asia and a 

 scab from Europe are causing serious 

 damage to some kinds of willows, espe- 

 cially in New England. Twig and leaf 

 diseases do not excite so much interest, 

 but their action is a perpetual drain on 

 the productivity of the affected trees. 



INSECTS AND DISEASE-PRODUCING 

 ORGANISMS may work as partners. As 

 we mentioned in connection with the 

 Dutch elm disease, an imported fungus 

 can make a destructive insect out of 

 one that is relatively harmless. It seems 

 possible, therefore, that introduced in- 

 sect carriers could similarly make dis- 

 astrous the two fungi that now are 

 destructive to the London planetree 

 and sugar maple. 



Sometimes an insect and a fungus to- 



