Galls on the leaf – normally regularly shaped domes above and sometimes below the upper surface – can be caused by a number of pests and diseases. Here we are interested in the ‘midge’ that causes galls on blackcurrant leaves. Galls sometimes materialize as larges round growths – such as the common Oak Apple gall. Cutting one of these open will reveal the maggot of the Oak Leaf Wasp, which lays its egg, then to develop into larva which causes the large gall.
The Leaf Midge lays eggs which develop into small maggots on the Blackcurrants. These then find their way to the leaves for food, causing the young foliage to become distorted, twisted, and then turning black. The Blackcurrant Leaf Gall Midge is NOT the same as the Big Bud Mite
Eventually this causes death of the shoot and a general weakening of the plant - not always serious and control can be simply by taking off the infected leaves, where you will probably find the small creamy-white maggot inside, and destroying.
As with all midges, the Blackcurrant leaf Gall midge is not easily controlled for there is no chemical control available to home users. Affected growths can be cut off and burned.
Treatment with a systemic insecticide suitable for food crops - such as Provado - will also be an option. Do not use at blossom - pollinating time. Provado uses Thiacloprid as its main active ingredient, and this is less of a problem to pollinating insects. But do not use before flowers have finished. Until then, simply pick off leaves. If nothing else, this will ease the problem for next year.
Image shows typical damage by a Gall Midge. Not on a Blackcurrant in this instance.
Leaf Midge - or Gall Midge
Organic gardeners suggest a dilute spray of ordinary washing up liquid. Maybe that is better for visible aphids!
Whichever method of control you use, doing nothing is not really an option, for the affected leaves are at the soft growing tips, which are basically providing for next year’s growth. It is sometimes said that there is not enough of a problem for any concern.
Young growth is essential for the benefit of any plant, and weakening of the foliage on fruit bushes will lead to a less productive crop. Producing fruit takes energy – lots of it!