WALNUT BACTERIOSIS. BACTERIUM JUGLANDIS 



PIERCE. 



By Ethel Mary Doidge, M.A., D.Sc, F.L.S. 



{Read, July lo, 1918.) 



The disease known as walnut bacteriosis was first described 

 by Pierce* as occurring in California, and on that account it is 

 often referred to as the " Californian Walnut Blight." In the 

 first paper he published a technical description of the organism 

 causing the disease and its effect on the host ; he had previously 

 published several more popular accounts in local agricultural 

 periodicals. t A bulletin published by R. E. SmithJ and others 

 in 1912 discusses walnut culture and diseases of the walnut in 

 California very fully, and classes the bacteriosis as by far the 

 most important trouble affecting the walnut in California. 



Geographical Distribution. — It is not yet definitely known 

 how widespread the disease may be in America. It is of serious 

 economic importance in California, and has also been recorded 

 from the Eastern States,§ where its presence has long been sus- 

 pected ; but it is only recently that the trouble in the Eastern 

 States has been proved to be identical with the Californian Wal- 

 nut Blight. 



It is very probable that the disease occurs in France, but I 

 have not seen any very definite statements in this connection. 

 In the colonies it is known to occur in New Zealand, || and it has 

 now made its appearance in our South African walnut i)lanta- 

 tions. For some years it has been suspected that the walnut 

 bacteriosis was present in this country, but specimens which were 

 submitted for examination werfe always in a very advanced 

 stage of decomposition, and most frequently had become inifected 

 secondarily with Gloesporinm epicarpii, which made an accurate 

 diagnosis difficult. During the last few years many walnut plan- 

 tations have been started, and as trees are still being planted in 

 large numbers, the diseases which effect walnuts are becoming 

 of greater economic importance to South Africa. During the 

 last season the identity of the South African walnut blight with 

 the walnut bacteriosis of California was definitely established, 

 and several districts where walnuts are grown were visited with 

 a view to discovering to what extent the disease had spread. 



A large number of trees have recently been planted in the 

 Oudtshoorn district, but most of the trees are still young, and it 



"^ Botanical Gazette (1901), 31. 273. 



iPacitic Rural Press (1896), 57. [25], 387. 



i California Agric. Exp. Station Bull, No. 231. (1912). 



California Fruit Grower (1896), 19, \^3^, 243; [16], 316. 

 § W. A. IBoucher, New Zealand Dept. of Agric. Kept. (1900), 334-335- 

 T. W. Kirk, New Zealand Dept. of Agric Rept. (1907), 167. 

 II McAIurran, S. M., Bureau of Plant Industry Bull.. No. 611. 



