Plant Doctor Archive

Not so perfect pansies

ALL my pansies end up with the same problem. I buy them from the nurseries and, after planting out, they look healthy and flower, but then the leaves turn yellow. When you touch the plant it falls over as it has no roots. My friends have experienced the same problem. Polyanthus, cyclamen and dianthus growing nearby don't seem to be affected.

THERE are a range of beetles and weevils, including grass grub, black vine weevil and wireworm, whose larvae feed on the roots of a wide range of plants and it can be difficult to identify exactly which one is causing the problem. Search through the soil for grubs - you may find some of the culprits. They can be 5-10mm long, some have legs others don't and their colour can vary from creamy white to brown, sometimes with dark heads. They might be in the potting mix when you buy the plants, but shouldn't be. They may also simply be in a restricted patch of your garden.

Vigorous cultivation of the area before planting can kill off many of the grubs already in the soil. It simply crushes them. Check the roots of the plants you buy carefully before planting to make sure they are not already infested and if you do find some larvae, or if the root system looks weak, take the plants back to the garden centre. You could also try using the granular form of the insecticide diazinon, available as Soil Insect Killer or No Insects Lawngard Prills. Follow the label instructions and take particular care not to use these products around any food crops, other than carrots and parsnips for the control of carrot rust fly larvae.

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