Plant Doctor Archive

Blooms & bugs

THIS year some of the blooms on my lovely dahlias (right) are full of bugs. What are they and what can I do to get rid of them? I don't like using toxic sprays so can you recommend something safe?

THE bugs are black aphids sucking sap from the petals. Serious infestations can cause distortion of the flowers but luckily they are quite easy to control. You might find they only affect a few flowers and if you cut these off and destroy them the others may not be attacked. However, if they are widespread you may have to take other measures. There are lots of products available to control aphids, many of which have low toxicity to humans. Some gardeners find a solution of up to one teaspoonful of washing up liquid (such as Sunlight) in one litre of water will control them if sprayed directly on the aphids. Fatty acid-based products, like Natures Way Insect Spray, are also effective but again need to be sprayed directly on to the aphids. The problem with both these sprays is they may damage the tender dahlia petals, so you could try using Mavrik, a low toxicity insecticide which is safe to use on delicate plants and has the added benefit of not harming beneficial insects like ladybirds.

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