/J /?. V.' i B, P. 1 i 'i fust 5, l'.KW. United States Department of Agriculture, BUREAU OF PLANT INDUSTRY— Circular No. 38. B. T. GALLOWAY. Chief of Bureau. ROPEAN CI RRANT RUST ON THE \ AMERICA. By 1'kui.kv Spaulding, Pathologist, Offict of Investigations in 'Forest Pa INTRODUCTION. During the past decade an intelligent appreciation of forestry meth- ods has been developed in this country. This lias produced in the Northeastern and North-Central States an increasingly insistent demand tor young trees suitable for the purposes of reforestation at a reasonable price. A large import trade has therefore developed. The white pine [Pinus strobus I..) has been the principal timber tree of the section above mentioned, and very naturally it has become the principal species used in reforestation. Hence, the import trade is largely concerned with this single species, and white-pine trees are now coming into the country at the rate of several millions a year. This is taking place with abso- lutely no inspection regulations other than local ones, which are utterly inadequate to deal with the problem. American plant pathologists have been anticipating the introduction of the European blister rust I Peridermium strobi Klebahn) on the white pine. On June 5, 1909, Mr. C. R. Pettis. New York State Forester, asked the writer to examine some three-year-old seedlings which were imported this spring from Germany. No fruiting bodies were found present on these trees; but a Foreman who had planted others of the same lot observed thai some were apparently diseased and gave so good a description that the writer was convinced that Peridermium strobi had actually been imported OD the trees. A personal examination on June 8 of Borne three-year-old trees which had been imported in 1908 resulted in the discovery of fruiting bodies of the fungus. Further search has Bhown that the disease is present. BO far as now known. only in trees from J. Heins >"hne, of Halstenbek, Germany. Fur- thermore, it has thus far been found only in trees which are now - 2 EUROPEAN CURRANT RUST ON WHITE PINE. three years old, i. e., of the seeding of 1906. But trees from this nursery have been distributed throughout the Northeastern States and Ontario. Trees of the same age from other European nurseries have been examined, but none of the disease has yet been found in them. It is apparent, then, that a very severe and general infection of the white- pine seedlings took place in this nursery in the year 1907. This con- clusion results from the two facts (1) that the fruiting bodies are situ- ated on the wood formed in the second year and (2) that the fungus is known to incubate for at least a full year on white pine before fruiting. Because of the general distribution of the disease in Europe all imported white-pine trees must be under suspicion until proved free of this fungus. LIFE HISTORY OF THE FUNGUS. The fungus Peridermium strobi Klebahn was at first thought to be a distinct species, but has subsequently been proved to be one stage of the blister rust of currants and gooseberries known as Cronartium ribicola Fisch. de Waldh. a The life history of the fungus is as follows : Spores from an infested currant or gooseberry bush are blown to some neighboring white-pine tree. There they germinate and attack the bark of young stems and branches. The mycelium vegetates in the soft inner bark until the second spring after infection took place. Early in the second spring the diseased bark becomes thickened and the stem of the young tree becomes swollen at the infected place for a length of one to several inches. In Germany the fruiting bodies break through the bark from April 20 to June 1. The fruiting bodies at first are light orange in color, rounded more or less, and project from the surface of the bark from one- eighth to one-fourth of an inch. Later they break open irreg- ularly and the spores are scattered by the wind. After the spores are scattered there is left a whitish membrane which is very fragile and which also is soon blown away or washed off by rain. This leaves only the empty fissures in the bark through which the fruiting bodies extruded as evidence of the presence of the fungus. These fissures are very char- acteristic to one who is skilled in such matters, usually being somewhat wavy in outline, longer than broad, and with the edges of the bark slightly elevated by the escaping spores. The spores produced on the white pine in turn infect currant leaves upon which they may alight. Here the period of incubation is relatively short, varying from 15 to 40 days. On the currant the fruiting bodies appear at first as tiny reddish dots on the under surface of the leaves. Later, the fruiting bodies form small thread-like tendrils, also on the under surface of the leaf. These spores may infect either the currant or the white pine. The spores pro- » Arthur, J. C, North American Flora, vol. 7, pt. 2, p. 122. 1907. fCir. 38J EUROPEAN CURRANT BUST ON WHITE PINE. 3 dueed on the white pine can not directly infect the white pine, but must attack the currant. On the currant the rust is not known to b( p nial, but on the white pine it remains alive as long as the stem or branch which it int. - FIELD CHARACTERS OF THE DISEASE. The characters mentioned below apply only to the disease in three- year-old ■ these are tie' only one- yet seen which were affei The affected tree has a peculiar stunted appearance so far as the top i- concerned, while the stem is swollen or enlarged abnormally. New growth is much shorter than on normal seedlings, never being over one- halt' the normal length. The stem is swollen at the int. cted place and is usually somewhat spindle thaped. In some case> it is swollen along the entire length of the second year's growth, hut when tins happi i- swollen irregularly, the bark having a bunchy appearance in pla A seedling with an abnormally thick Btem or one which is irregularly thickened without any apparent injury to the bark is diseased. A nor- mal seedling will have a stem winch is quite uniform in size throughout each growth. Any injury, such as a bruise, will cause swelling only at the edge of the broken bark. Of course the fruiting bodies them- selves are the best character by which to recognize infested white pines or currants, but on the former they are present only in the spring, while on the latter they are present during the late summer and fall. There is a native rust of wild currants which is common in some sections, and this must not be confused with Cronartium ribicola, which is entirely distinct and of different appearance. DAMAGE CAUSED BY THE RUST. The knowledge possessed by American pathologists as to the amount of damage caused by the rust is mostly based on statements in Euro- pean literature. On the currant there is very small damage, but this is the most dangerous stage in the life history of the fungus, owing to the possible infection of any neighboring white pines. On the white pine the damage is very considerahle. Young trees are killed outright and small branches on large trees are killed. In certain places in Europe, notably in Holland, at Oldenhurg. Germany, and at Moscow, Russia, this disease is so serious that the cultivation of white pine has been abandoned. In other places the rust is abundant, and especially in the vicinity of Hamburg, Germany. METHODS OF COMBATING THE RUST. Very briefly stated, the practical method- of combating this di- are as follows : (1) Examine all currant bushes near infected plantations or nurseries of white pine and hum all that are affected; or, better, destroy all cur- ICir. 38] EUROPEAN CURRANT RUST ON WHITE PINE. Approved : James Wilson, Secretary of Agriculture. Washington, D. C, July 3, 1909. O [Cir. 38] a- ; rants in the vicinity, if practicable. This should be done from July 15 to the fall of the currant leaves. (2) Inspect imported white-pine trees and burn all that show any evidence of the disease. (3) Inspect for at least two years all white pines located near infected currant bushes and burn all that become infected. CAUTION. Owing to the peculiar character of this disease it can not be detected in wbite-pine seedlings by any possible method of dock inspection unless the fruiting bodies are present or have been present. The fungus lives for one year in the bark without giving external signs of its pres- ence and can not possibly be detected during this period. In order to have effective inspection of affected trees in the field the most expert supervision is necessary. Great care must be taken that every seed- ling is located and examined, all dead and dying ones removed and burned, and every suspicious looking tree burned. Wherever necessary, the Office of Investigations in Forest Pathology will give advice and supervision. Each State is now taking up the problem and will, it is hoped, be able to cope with the situation. In view of the great danger from this disease it seems best to advise that no more white-pine seed- lings be imported. It is believed that all large recent importations of European stock have been located and so can be promptby inspected, but it is entirely probable that many private importations have been made which have not been located. It is imperative that the presence of all such stock should be reported to the State or National authorities, so that prompt inspection can be made. Otherwise all efforts that are now being made to eradicate the disease may be in vain. UNIV. OF FL LIB. DOCUMENTS DEPT. ":;-- ^.„ \ U.S. DEPOSITORY i