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GOOSEBERRY SAWFLY ON THE JOSTABERRY

Posted by Rosemoor Garden on 23 Jun 2009 at 11:26 AM

For the first time last year (2008) we had a bad attack of Gooseberry Sawfly on the Jostaberry. The plant is about 14 years old and this was the first time I noticed any sawfly damage.

I thought it might be something to do with the milder winters but last winter (2008/9) was the coldest for a long time – minus 11 deg C in the veg garden. There were three generations last year and each generation contained 100’s of larvae. The damage was so bad that it severely weakened the plant.

The term Common Gooseberry Sawfly covers a number of closely related species which attack gooseberries and currants. The larvae of the Common Gooseberry Sawfly are green, up to 20 mm long, with a black head and black spots.

The larvae over winter in the soil beneath the plant as a cocoon. Adults emerge in April and lay eggs in slits alongside the veins on the leaves. They hatch in about a week and the larvae feed for about a month before dropping to the ground to pupate in the soil and emerge in about 3 weeks to start the next generation. During this time they can completely strip the leaves back to the veins.

There can be 3 generations through the summer and the third generation will pupate in the soil to overwinter.

The Jostaberry is an interesting hybrid between a Blackcurrant x Gooseberry hybrid x Blackcurrant x Worcesterberry. So you can see why the sawflies would like them as they have currants and gooseberries in the parents. But it’s still a mystery to me why the attacks should start now.

This year the attacks started on the 7th May and we are now dealing with the second generation. Our only control is to pick them off by hand. The Rosemoor Veg Garden volunteers gladly gave us a hand.

 

You might also try the Nemasys caterpillar control product containing eelworms, or a pyrethrum spray.

 

Garry Preston, Fruit and Veg Gardener

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