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AMERICAN FORESTRY 



Wild currants and gooseberries, which transmit the 

 disease to the pines, are prevalent in the regions where 

 these pines grow. While the disease is known to be 

 present now only in the Northeastern States, it would be 

 a matter of but a few years for it to reach some parts of 

 the Pacific Coast or Rocky Mountain regions on pine 

 nursery stock if shipment continues without restraint. 

 The forest conditions there are such that if the disease 

 once reaches the native forests there is no possibility of 

 controlling it. This disease threatens not only the 

 Northeastern States, but also the Pacific Coast and the 

 Rocky Mountain regions. 



Whilethe situation in the Northeastern States, where 

 the White-pine Blister Rust is now present, is critical 

 and much worse to attempt to handle than it was in 1914 

 and previously, yet the nature of the disease is such that 

 there is even now a fair chance to control it, if unanimity 

 of action and adequate authority can be secured. The 

 areas which are badly infected vary in size from only a 

 few square yards up to one of hundreds of square miles. 

 The only thing which will prevent any further spread of 

 this disease in any one of these infected areas is the 

 removal of all wild and cultivated currants and goose- 

 berries, and of the diseased pines within those areas. 

 Otherwise the disease will live in the pines as long as 

 they remain alive and will be a constant source of danger 

 to that neighborhood, as well as to the entire country. 



WHAT SHOULD BE DONE. 



Any person owning a plantation of white pines im- 

 ported by himself or through a broker, or bought of a 

 nurseryman without a definite guarantee that they were 

 raised in this country from seed, may find this disease 

 present. Although many American nurserymen in the 

 past have raised most of the white pine stock distributed 

 by them, it has been the rule rather than the exception 

 for them to supply part of their trade with imported 

 stock. A very large proportion of this imported stock 

 has been shown by actual experience to be infected. 



If an owner believes he has found any symptoms 

 whatever of this disease, his best course is to take speci- 

 mens in generous quantity, and in order to insure a 

 prompt reply, mail them to the writer at the Bureau of 

 Plant Industry, Washington, D. C. A positive iden- 

 tification of the disease will be made, so far as that is 

 possible, and advice given concerning further action. 



It is inadvisable for any owner to attempt to handle 

 the disease without expert advice. Experience with this 

 disease is very necessary in order to determine the 

 extent of the disease and the best method of handling 

 it in each case. Pieces of pine branches of trees of 

 course may be sent as they are cut from the tree. 

 Diseased currant or gooseberry leaves should be laid flat 

 between folds of newspaper or blotting paper and then 

 mailed in the ordinary way. Any owner who believes 

 he has the disease upon his property should remember 

 that a diseased pine will remain diseased as long as it 

 lives, and if no attempt is made to control the disease 

 upon his property he will be the first to suffer from it 

 and will also probably suffer the greatest damage. 



DO NOT MISTAKE IT. 



In the Eastern States a native parasite often occurs 

 upon the leaves of wild currants and gooseberries which 

 forms yellow spots upon the lower surface of the leaves. 

 These spots are usually from an eighth to a fourth of an 

 inch in diameter (much larger than the blister rust spots) 

 and do not have the powdery appearance that character- 

 izes the blister rust disease. 



DESCRIPTION OF THE DISEASE. 



This disease was not discovered on pines in this 

 country untrt 1909. Then it appeared as shown on the 



accompanying color plate in figure "A." This is a full- 

 sized drawing of a 4-year-old white-pine tree affected by 

 the disease. The yellow spots with irregular white edges 

 are the open blisters of the parasite breaking through 

 the smooth bark of the young tree. The white edge is 

 part of a very thin, rather tough, white membrane. 

 This, at first, is completely closed and is somewhat 

 rounded, much resembling a blister. After a few days 

 the top of the blister breaks loose and falls off, leaving 

 merely the ragged edges of the membrane projecting up- 

 right around the cavity in the bafk. Upon the breaking 

 of the blister, it is seen that the entire cavity within is 

 filled with a mass of very fine, bright yellow powder 

 (spores). This is the stage of development shown in the 

 colored plate. Each grain of this powder acts as a seed 

 in starting the disease in a new place. It will also be 

 noted that there is a certain amount of irregular swell- 

 ing of the stem and branches shown in this figure. 



Such swelling is very characteristic of this disease. 

 Before the blisters have formed in the bark, the young 

 tree may show this same irregular swelling, but with ab- 

 solutely no external break in the bark tissues. These 

 blisters are found from the latter part of April to about 

 the middle of June, depending somewhat on the earli- 

 ness of the season and the locality. Very curiously, 

 the parasite causing this disease cannot spread directly 

 from pine to pine, but must live for a time upon the 

 leaves of wild and the cultivated currants or gooseberries. 

 The yellow spores from the pine infect the leaves of cur- 

 rants or gooseberries, and after about two weeks produce 

 numerous tiny masses of orange-colored, mealy powder 

 on the under surface of the leaves. These masses are 

 hardly larger than the head of a pin and may be very scat- 

 tered or may be so abundant as to form an almost con- 

 tinuous dusty layer, from which clouds of yellowish 

 powder float when the leaf is disturbed. This yellow 

 powder is a second form of spore, which in turn is able 

 to infect more currant or gooseberry leaves. 



This stage of the disease occurs from June 15 until 

 killing frost, when the leaves of the currants fall. 



Figure "B" shows a flowering currant leaf affected 

 with this stage of the disease. 



Figure "C" shows a portion of this leaf much magni- 

 fied. The infection of new currant leaves at this stage 

 may be repeated and a considerable number of genera- 

 tions of this stage of the disease developed during the 

 season . Upon the beginning of cooler weather, however, 

 there is produced upon the lower surface of currant and 

 gooseberry leaves a third form of spore. These occur 

 in the form of small groups of hairy outgrowths, each of 

 which may contain from two to ten or a dozen filaments 

 hardly one-fourth inch high, usually arranged in small 

 circles. 



Figure "D" shows this stage. Upon these filaments 

 are produced numerous tiny spores. These cannot at- 

 tack the leaves of currants or gooseberries but are able 

 to attack the young bark of white pines. All of these 

 three forms of spores are mainly distributed by the wind. 

 The last -mentioned form of spore is found from the latter 

 part of July until the leaves fall , and infection of the pines 

 occurs immediately. When one of these spores alights 

 upon the bark of a young pine, it begins to grow as does 

 a seed, and pushes its roots into the living bark tissues. 

 After once gaining entry to the soft bark it grows rather 

 slowly and there ensues a "period of incubation" during 

 which nobody can say whether the tree is diseased or 

 not. This period varies from somewhat less than a year 

 up to six years or more before a visible development of 

 the disease can be detected. At the end of this incuba- 

 tion period more or less swelling usually develops in the 

 bark at the affected point, and is later succeeded by the 

 formation of the blisters. 



