Q & A: How do I protect my roses from aphids?

Aphids suck sap out of new growth on roses and distort bud formation.

Aphids suck sap out of new growth on roses and distort bud formation.

Q: The buds of my roses are covered with aphids. The blooms are all distorted when they open. What can I do to protect my roses?

A: Soft, sappy new growth on roses and other plants attracts aphids. There are various species of aphid and most are specific to particular groups of plants. They're a menace because they transmit viruses with their needle-like mouthparts, and sooty mould grows on the honey dew they excrete. 

Aphids cluster at the tips of new growth so a quick, effective control is to squash them with your fingers. Aphids are targeted by ladybirds and other beneficial insects and insectivorous birds so attracting these to your garden will help knock back aphid numbers. Aphidius colemani, a parasitic wasp (from zonda.net.nz), also predates on aphids.

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Sprays need to be used very carefully because if they kill aphids there's a good chance they'll kill beneficial insects like bees and other pollinators too. Spraying with Neem oil knocks back the aphids but won't harm larger beneficial insects. Mineral oil or pyrethrum kills aphids – but it harms good bugs too.

Be selective when applying; target only pest-infested areas or individual plants. A windless evening is the best time to apply sprays if bees are active during the day. Spray affected plants every five to seven days until infestations are under control. With all sprays, test on a just few leaves first to ensure your plants do not react negatively to them.

These DIY spray recipes have natural ingredients but that doesn't mean you shouldn't be just as careful applying them.

The fatty acids in soaps dissolve the exoskeleton of aphids, whiteflies, thrips and mites and they dehydrate. Use a liquid soap, such as castile soap, which contains no fragrance or other chemicals. Add 1 tablespoon soap per 1 litre water and shake. It needs to come into contact with pests to work.

Tomato foliage contains a poisonous alkaloid known as solanine, which is deadly to many pests, including aphids. Place foliage in an old food processor, cover with water, add 2 tablespoons cornflour and mix. Strain before using on roses and other ornamentals.

Knock back infestations of aphids and other soft-bodied insects and deter them from coming back with this potent mix. Wear gloves when making this, as the chilli can cause skin irritation and pain if it gets into your eyes. Blitz 5 cloves garlic and 1 habanero chilli (fresh or dried) in a blender with ¼ cup of water until well chopped. Steep for one hour. Strain through a fine sieve. Discard the solids, then mix the liquid with 750ml hot water and ¼ teaspoon soap or dishwashing liquid. Transfer to spray bottle.

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 - NZ Gardener


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