Plant Doctor Archive

Pests on raspberries

CAN you advise me when to spray autumn raspberries to avoid a small worm that develops as the fruit enlarges? I was disappointed to lose most of my crop this year. Also, when is the best time to prune summer-flowering hebes? They have grown so much this season due to excess moisture.

WORM-LIKE pests in raspberry fruits are probably the larvae of moths, butterflies, beetle or flies, but without a sample it's impossible to tell exactly which is causing the problem on your plants. There are, however, precautions you can take to reduce the chances of it recurring next year. In most cases the adult pest is likely to lay its eggs close to the flower or developing fruit so that on hatching the grub can bore into the fruit.

One of the most effective ways to reduce damage is by applying an insecticide to the immature fruit to prevent the larvae boring into the fruit. As soon as flowering is finished and berries start forming, I'd try spraying every 14 days with Success Naturalyte or dusting regularly with Derris Dust. Both are naturally derived insecticides and safe to use on fruit during the early stages of their development. Follow the product label recommendations.

As for hebes, prune them as soon as possible after they've finished flowering. It depends on your local climate and the variety of hebe, but generally it's best to avoid cutting them back in late autumn as that encourages new growth during wet and humid winter weather ,which can lead to disease.

It might pay to put off pruning until early spring and then only give a light trim to remove old flower heads. Don't cut back into old wood as, with some varieties, it can fail to regrow, though you can remove the odd whole branch if necessary to thin out a dense plant.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.