The leaves of my blackcurrants this year were all blistered with raised lumps, but l never found any insects on them,what caused this problem and how I can prevent it occurring next year?
The cause was an attack by the currant blister aphid.
This particular greenfly feeds under the leaves of red and black currants, resulting in the raised blisters you have seen.
The blistering remains after the pests move off to their summer host plants.
Winged adults return to the currant bushes in autumn, lay their eggs which overwinter on the bushes..
The best way to prevent damage, is to spray the bushes with a winter wash in the dormant season (December to end of February) to kill the eggs.
This Spring, many of my blackcurrant shoots were crumpled. I pruned these out,but as they sent out further shoots,these too,were crumpled,and the leaves were twisted.
What is causing this, and is there a cure?
The damage has been caused by the blackcurrant leaf midge.
There are three or more generations each year.
The adult midges lay eggs in the new growths and many larvae feed together, resulting in the damage you describe.
The insects then pupate in the soil to emerge as adults a couple of weeks later to repeat the cycle.
To control it cut out the affected shoots and spray with a suitable insecticide to reduce re-infestation.
Next year, apply the spray when the flower buds become visible.