Gooseberry sawflies lay eggs on your gooseberry plants. When the caterpillars hatch out they can devastate the plant leaves so that you end up with a bush that looks like this -
They also attack red and white currant bushes. The fly arrives anytime from April onward. The female sawflies lay eggs on the underside of leaves, low down in the center of the bush, so the young larvae go unnoticed until they have eaten their way upwards and outwards, devouring the leaves as they go - often defoliating a bush completely.
They can have several generations in one season so it is important to keep an eye on the plants throughout the summer.
Regularly check the plant for sawfly caterpillars and pick them off by hand.
You can also spray the plant with Pyrethrum which is an organic treatment effective against sawfly caterpillars. Pyrethrum is an extract from the flowers of the Chrysanthemum. Pyrethrum's natural instability - light and the oxygen degrade pyrethrines quickly - works as well in its favour: there are no residues left after a few hours so it is safe for humans, bees and birds. It is effective against a range of pests - not just gooseberry sawfly.
Pyrethrum works on contact with the insect so it is advisable to spray in the evening when beneficial insects such as bees are not active.
To use Pyrethrum against Gooseberry sawfly, simply spray onto the plant where the caterpillars are present. You can buy Pyrethrum concentrate suitable for diluting and spraying from your own sprayer or as a ready diluted product in a 750ml spray.