38 THE WALNUT — ENEMIES. 



of the diseased tissue shows the presence of a bacillus, the organism being constantly 

 preseht. Pure cultures of the bacillus have been obtained from spring inoculations, the 

 tissue of the nut husk being too firm in the latter part of the season to test.the action of 

 the organism with any degree of certainty. Observations indicate that unfavorable root 

 conditions for the trees may have an important bearing on the primary development of 

 the trouble." 



This disease was reported as being prevaleiit among walnut trees in 

 the central part of the State in 1891. Since then, however, the trees are 

 said to have recovered, and, on investigation, it was found that it was 

 not this disease, but the trouble was caused by the soil drying out in the 

 summer, causing the trees to lose considerable of their foliage and the 

 nuts to shrivel. 



This bacterial or mysterious disease has made its appearance in vari- 

 ous walnut orchards in different parts of the State, and threatens to seri- 

 ously affect the walnut groves unless checked by some effective remedy. 

 The disease has been termed Bacteriosis of walnuts, by Prof. Newton B. 

 Pierce, Assistant .U. 8. Pathologist, and is described* by him as follows: 



" Bacteriosis of walnuts is a bacterial disease of the nut, branch, and leaf parts of the 

 Persian walnut {Juglans regia). Inoculation experiments have demonstrated that other 

 forms of Juglans may also be artificially infected by the organism. Under natural con- 

 ditions the hut of the Persian tree is very commonly infected in the blossom, at or about 

 the time of pollination. Secondary infections may take place through any portion of 

 the hull of the tender nut, especially during the more rapid growth of spring. The new 

 shoots and leaves may be infected at any portion which is tender and rapidly growing, 

 but most of these infections actually take place at or near the growing point of such 

 shoots, and oiily become distinct to the naked eye after rapid growth has left the infected 

 part some distance down the branch. Injury to the cells of the nut, branch, or leaf parts 

 is effected by the organism by means of an enzym, or ferment. This enzym acts chem- 

 ically upon the tissues surrounding the point of infection, destroying the cells and jjre- 

 paring tnem as pabulum for the multiplying bacilli. This enzym is capable of destroying ' 

 the tender cells of the hull, newly forming shell, and the contents of the kernel. As any 

 or all of these parts become hard with age, less injury is done through infection by this 

 germ. In case of blossom infection the nut is usually badly diseased, and, in a majority 

 of cases, will fall when one third or two thirds grown. Lateral infection of the hull is 

 less likely to wholly destroy the nut, but very commonly causes it to fall or the hull to 

 adhere to the shell in such a manner as to make the nut unfit for market. Wherever 

 the nut becomes infected the parts eventually turn back, owing to the oxidation of the 

 tannic acid. When the disease is actually spreading, however, a circle next the healthy 

 ti.ssue usually assumes a watery appearance, which may be used as a character quite 

 distinctive of this disease. This watery ring is where the enzym is acting upon the 

 healthy cells often in advance of the presence of the organism itself. The characters 

 here given for infected nuts are equally applicable to infected branches. 



"The germs of this disease are capable of wintering either in the diseased branch or 

 nut. 



"The treatment of walnut bacteriosis has already shown some beneficial results. 

 Over forty acres of spraying experiments were set on foot last spring. This work was 

 done with the leading fungicides, but as the disease is now known to be of bacterial 

 nature, it will be attempted to prevent the same by means of some of the leading germi- 

 cides, with which, applied as winter sprays, it is hoped to obtain even better and cheaper 

 results than with the standard fungicides. As this work is still in progress, and certainly 

 cannot be completed inside of another year, it cannot be summarized at this time. It 

 may be said, however, in absence of the perfection of better methods, that the Bordeaux 

 mixture applied to the tree just before the growth of spring starts, and again to the nuts 

 as soon after pollination as possible, will certainly prevent a portion or the infections 

 which would otherwise take place. It has also been found of advantage to gather and 

 destroy diseased nuts, and to prune away diseased branches during the winter. It is 

 hoped that another season given to the testing of germicides may develop some more 

 specific manner of preventing infection. No treatment looking to the cure of diseased 

 nuts or branches maybe hoped for; all treatment must be preventive." 



In the " California Fruit-Grower " of October 17, 1896, Professor Pierce 

 adds to the above the following note: '<■ 



"The walnut disease has a wide distribution on this coast, extending as far north as 

 Stockton, and south to San Diego County. There probably are, however, large inter- 

 vening regions not affected. The disease does no special damage to the year-old wood 



* In California Fruit-Grower, Beptember 26, 1896. 



