71 



increased up to a certain point, bat subsequently has remained 

 stationary, and in spite of the attack a small crop is always 

 obtained. Notes on the resistance to the disease shown by 

 some varieties or individual bushes of black currants will 

 be found in the section on Methods of Control. Owing to 

 the fact that the extent of this resistance is so variable, no 

 list of resistant varieties is given. Young bushes frequently 

 appear to resist attack for 4 or 5 years but subsequently break 

 down, and a variety should not be judged until it has been 

 tried for a considerable period. 



Red Currant. Theobald* states that " the mites produced 

 a dense growth of buds, every here and there, which were 

 found to be teeming with them. At the same time the shoots 

 bearing the attacked buds were abnormally swollen, many 

 twice the thickness of normal ones.*' 



Gooseberry. In the case of the Gooseberry the noticeable 

 features of the attack concern the young shoot, soft tender 

 leaves, and to some extent the fruit blossom. The mites 

 cause a marked blistering and, according to Miss Taylor,! 

 " after a bad attack the whole leaf surface, the veins and 

 the petiole become covered witn succulent outgrowths." 

 " Leaves so attacked are considerably under the normal size 

 and the main stem itself is reduced in length. The leaf colour 

 is yellow green and the tree has a generally unhealthy colour." 

 Obvious injury only occurs early in the season later, when 

 the leaves and shoots harden, no further damage is done and 

 the later- formed leaves are normal in size. 



The reason for the difference in the form of attack on the 

 three plants would seem to lie in the nature of the buds. 

 The black currant bud is somewhat loosely made, and hence 

 the mites can penetrate to the centre. In the red currant 

 and gooseberry the buds are tightly compressed and the mites 

 cannot work their way in.J 



Description and Life-History. The general appearance of 

 the mite when highly magnified is shown by Fig. 2, but the 

 animal is only about T ^ F inch in length, and if a big bud is 

 cut open, the mites are hardly discernible to the naked eye ; 

 even through a pocket lens they appear only as minute white 

 specks. 



From July throughout autumn and winter and until 

 March the mites live mainly inside the buds, where eggs are 

 laid and fresh generations are produced. During a period 

 covering roughly the months of March, April, May and June 

 the diseased buds either dry up and die, or produce distorted 

 foliage, and the mites are forced to migrate to fresh quar- 

 ters. When weather conditions are favourable that is to say, 



* Theobald, *' Insect Pests of Fruit, 1 ' p. 241. 



f- Taylor, Journal of Agricultural Science, VI, p. 131. 



+ Taylor, loc. cit., p. 133. 



