316 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
DISEASE OF THE BLACK CURRANT 
Caused by the Gall Mite, Phytoptus ribis. 
By John H. ^YILS0N, D.Sc, F.R.S.E., St. Andrews University. 
No enemy of the fruit-grower has of late made more rapid, insidious, 
and certain advance than that which has chosen the Black Currant as 
the victim of attack. At almost every centre in Fife where I have 
lectured during the present winter — from Dysart to Dunfermline, and from 
Leven to Xewburgh — I have received information of the prevalence and 
spread of the Currant-bud disease. So widespread and serious has it 
become, and so mistaken are the opinions of many horticulturists on the 
subject, that there is ample occasion for setting forth what is known of the 
life-history of the pest, and at the same time of pointing out what may 
be done to check its ravages. 
It is not known how it originally got into our gardens. Possibly 
enough it may have for centuries found a home in the buds of the wild or 
strayed Black Currant. The earliest reference to the disease in Scotland 
seems to date back fifty years.* It was not until twenty years later, 
however, that anything definite was known of its cause. Since then the 
disease has secured a firm hold, and made rapid progress in all directions. 
My earliest practical acquaintance with it was from material sent me in 
1889 from the Crieff district, where at that date it was making great 
headway. In the end of May 1891 I had specimens forwarded from 
Auchterarder to report on, and these were accompanied by a similarly 
alarming account of the havoc wroughc. 
A very little experience is needed to diagnose the disease, the infested 
buds being much larger and rounder than the healthy ones. The 
abnormal swelhng is quite evident in the early winter. The illustration 
(Fig. 118, 2), drawn in December from a Newburgh specimen, serves to 
show the characteristic appearance of the " big buds," a healthy shoot (from 
a seedling) being also figured for the purpose of comparison. If one of 
the swollen buds be opened at this time it will be found to be green and 
spongy inside, and if the contents be shaken out on a glass slip, and 
eiiamined under a highly magnifying microscope, the cause of the swelling 
will be at once rendered visible, the field of view being more or less 
crowde;! with mites of unmistakable character. It should be carefully 
remembered that they are of extreme minuteness. With the keenest 
eyesight it is possible to observe them, against a suitable background, 
when one knows precisely where to look for them ; but, seeing that they 
cannot be recognised at all unless under special circumstances, they may 
virtually be held to l)e invisible to the unaided vision. The largest range 
from to Yr,(i of iiich in length. When very greatly enlarged they 
present the form figured. (Fig. 118, 4.) Unlike such mites as the so-called 
* Soe Ornierod's Handbook of Insects, &c. 
