WALNUT BACTERIOSIS. 4^9 



••Iried prematurely and became rotten. English and French 

 varieties were both affected. 



At Potchefstroom. in the Transvaal, one tree is known to be 

 affected, and it is said to drop all its fruit every year ; and in 

 Natal, at Donnybrook. bacteriosis has lieen found to be the cause 

 of a blight on the leaves and young shoots of some hundreds of 

 young trees which have not yet come into bearing. 



Characteristics of the Disease. 



Like most of the bacterial diseases attacking the parenchyma 

 and classed by Smith as leaf (and fruit) spot diseases, walnut 

 bacteriosis only attacks tender growing parts olf the tree, such as 

 the young nuts and branches, the young leaves and the petioles. 

 This being the case, it is naturally also severe on nursery stock. 



On the branches the young infections always appear on 

 young succulent growth, usually near the growing point ; the first 

 indication of infection is a small dark green water-soaked area, 

 which gradually increases in size ; the central portion becomes 

 discoloured and finally black, but so long as the area of infection 

 is increasing, the blackened area is surrounded by a zone of dark 

 green water-soaked appearance. As the shoot becomes hard and 

 woody the active development of the disease is checked and it no 

 longer continues to involve fresh tissues, the whole diseased area 

 then turns black, and in many cases the affected tissues shrink 

 and crack. These stem lesions are frequently two and three 

 inches in length, and in serious cases all the tissues from the bark 

 to the pith are involved ; but frequently the organism only pene- 

 trates slightly into the wood. 



Infection on the leaves and petioles begin in a similar way to 

 those on the branches, forming small water-soaked spots which 

 turn black, these are usually more or less angular in outline, and 

 when numerous they coalesce and form large discoloured areas. 

 The petioles and veins are also frequently attacked, and in the 

 latter case the leaflets become puckered and deformed in various 

 ways. Smith* states that the disease does not cause any serious 

 defoliation of the trees, and in the cases which have come under 

 my personal observation this was certainly the case ; the disease 

 did not affect the general health of the tree to any very noticeable 

 extent. It was reported that, subsequent to the serious dropping 

 of the nuts at Clocolan, noticed above, the leaves began to fall 

 and the tree became practically defoliated, but whether this was 

 due to the bacteriosis or to- some other cause I had no opportunity 

 of ascertaining. It has been reported from elsewhere that the 

 young shoots which are attacked drop their leaves prematurely, 

 but further observations are required on this point. 



From the economic point of view the bacteriosis on the 

 young nuts is the only phase of^the disease which is of serious 

 importance. The bacteriosis on the twigs and leaves ordinarily 

 does very little injury, and the disease would be of very little 



* California Expt. Station Bull. No. 231. 



