Plant Doctor Archive

Bugs and diseases

CAN you tell what is eating my tamarillo tree and how I can get rid of it? The new leaves just seem to get eaten and fall off.

Also, the leaves on my mint are falling off and other herbs leaves are yellowing. Any tips?

JUDGING by the size of the holes in your tamarillo leaves I suspect green looper caterpillar to be the culprit. The adult moth, known as the silver y moth, can often be seen flying around in the evenings sipping nectar from flowers. The caterpillars are bright green and quite large, 35-40mm long when fully grown. They are voracious feeders and can damage a wide range of plants, usually feeding underneath the leaves.

Once your tamarillo is fully grown, a little caterpillar damage won't affect it, but at this young stage you should take some action. With only one plant you could probably control the caterpillars easily by checking the leaves regularly, say once a week. If you see a new hole appearing, look under the leaf for the caterpillar, pick it off and squash it. If there's also damage occurring to other plants in the area, you could spray with Success Naturalyte, which is effective against caterpillars but safe for other garden insects.

Many varieties of mint are susceptible to rust, a fungus disease that usually causes leaf yellowing and leaf drop. Most other herbs don't get rust, but similar symptoms in pot-grown herbs could be caused through excessive watering combined with lack of nutrients. I suggest you cut the mint and other affected herbs back to within a centimetre or two of the soil and repot them into a fresh potting mix which has the nutrients to encourage new growth.

Make sure the pots drain freely. While you can often get away with the pots standing in saucers filled with water over the warm summer months, remove the saucers for winter to allow rainwater to drain away quickly. Feed your herbs occasionally through the growing season with liquid fertiliser to encourage new growth for a good supply of herbs for the kitchen.

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