714 A NATIONAL PLAN FOE AMERICAN FORESTRY 



mon. One which appears particularly virulent is the willow blight, 

 caused by a leaf and a twig fungus working in partnership, both of 

 them introduced. This disease in the willows of the Northeast has 

 made a record for quick killing. It is destructive in this region 

 on several native willow species. If in its spread over the country 

 it is found to be equally virulent in regions farther south and west, 

 or if forestry developes further in the direction of cellulose production 

 so that willow can become important for wood production in bottom 

 lands, this disease may yet prove very serious. The willow is the 

 one tree best adapted to the holding of the soil on the banks of 

 streams in some parts of the country, particularly in the Middle 

 West. It is impossible to predict to what extent flood-control 

 problems might be aggravated by the loss of the willows. There is 

 no prospect of direct control for this willow disease, but there is an 

 unusual chance for the substitution of resistant willow species or of 

 resistant varieties of susceptible species for the willows that are 

 destroyed. The short generations and easy vegetative propagation 

 of the willow greatly facilitate breeding of resistant varieties. 



The larch canker illustrates a very different type of a recent im- 

 portation. This larch disease has long been troublesome in European 

 forests. It was brought to this country on imported stock from 

 Scotland a score of years ago. Because of the small amount of larch 

 in the locality where it was introduced, it spread slowly, and since its 

 discovery the entire eradication of the known cases has apparently 

 been successful. So far as known it no longer exists in this country, 

 but some years of follow-up work and more extensive reconnaissance 

 are necessary before it will be safe to say that the fungus has not suc- 

 ceeded in establishing itself anywhere in our native larch. Had the 

 disease been introduced originally into a region containing much 

 larch, the story of this introduced disease would have less chance of 

 having a happy ending. 



The so-called Dutch elm disease which was apparently introduced 

 into Europe has done tremendous damage in the elms of the low 

 countries and has now extended into the British Isles and through 

 Middle Europe. It has been found recently in Ohio; but in spite of 

 the most energetic search, in which the cooperation of the public and 

 the commercial tree surgeons has been enlisted, it has been discovered 

 to date on but eight trees. Wherever found it has been eradicated. 

 While the American elm is known to be highly susceptible, we have 

 reason to hope that the disease is not yet present elsewhere in the 

 country or that conditions in this country, as for example the absence 

 of one of the insects which appears to aid in its spread, will prevent 

 its active operation in our elm species. The loss of the elm would, 

 of course, reduce our timber resources in certain locations and for 

 certain purposes, and make a tremendous inroad on our tree resources 

 from the aesthetic standpoint in the North and East; in New England 

 it is more important as a street tree than all other species together. 



One of the most recent attacks of a possibly introduced disease is 

 affecting the two most important pines of the northeastern States. 

 Both northern white and Norway pine are being killed by a resinosis 

 at the base of the trunk in three New York plantations. If not dis- 

 tributed on nursery stock, this disease will probably be unable to 

 spread rapidly. However, in forests it is obvious that a slow but 

 sure spread can ultimately be quite as serious as a more rapid spread. 



