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Aphids — the number one garden pest

They transmit diseases, attack new buds and suck the sap from our plants. Aphids — plant enemy number one.

Aphids Aphids must be the most pervasive garden insect pests of all. As soon as any new growth appears in spring, aphids seem to materialise out of nowhere. They come in all sorts of colours and attack a wide range of plants.

These soft little critters are real trouble-makers in the garden. While their damage is not immediately obvious, they suck sap directly from the plant and, because they always attack the newest growth, this sucking can damage the most important growing parts.

What problems do aphids cause for a plant?

  1. Sap is the plant´s food source. When aphids suck sap from a plant, the plant becomes weaker and weaker.

  2. Because aphids attack the new buds, the resulting leaves and flowers never open properly and they remain puckered and curled.

  3. Most damaging of all, aphids can transmit serious virus diseases from one plant to another.

  4. During a particularly bad aphid infestation, the sticky residue they leave behind on the plant grows sooty mould, an unattractive fungal growth. Sooty mould reduces the plant´s ability to photosynthesise.

Why are aphids so successful?

AphidsAphids look very vulnerable, but they have one major weapon that helps them to be a winner in the survival stakes: they can multiply at an incredibly rapid rate.

As soon as the weather warms up, aphids begin to reproduce rapidly. Their rate of increase depends on temperature and it´s always highest in the moderately warm spring period — they´re not particularly happy when it´s very hot or very cold.

AphidsAphids are great survivors. When conditions aren´t entirely to their liking, adult aphids can lay eggs that will remain dormant, waiting until better times arrive. When conditions are good, they´ll bypass the egg-laying part of the process and give birth to live young. They can develop seven or more generations in one year and when the plant becomes too crowded, some members of the colony will develop wings and fly away to search for a new food source. Aphids are nearly all female, and they don´t even necessarily need to have both sexes for reproduction.

Ants protect and care for aphids, just like miniature dairy farmers. They build shelters for them, chase away predators and collect their eggs. In return, the ants are able to feed off the aphids´ honeydew secretions.

How do you get rid of aphids?

Squash and discourage

Aphids can simply be squashed between your fingers (although it´s probably more comfortable to wear rubber gloves!), hosed off or sprayed with a soap and water mixture. Make sure you use soap, and not detergent.

Give succour to their enemies

Encourage natural aphid predators, such as birds, ladybirds and hoverflies. Yates Phacelia has a pretty blue flower that attracts hoverflies into the garden.

Hit them where it hurts

Use a contact insecticide to directly shoot down aphid colonies. A low toxic synthetic pyrethroid like Mavrik will give good aphid control.

Attack From Within the Plant

Systemic insecticides work from within the plant. Confidor is an effective, low toxic and long-lasting suggestion.

Home-made insecticide and fungacide

60ml liquid seaweed fertiliser (or other liquid fertiliser)
1 tsp dishwashing detergent
2 Tbsp baking soda
1 litre water

Mix together all ingredients and spray on infested plants once a week.

The liquid fertiliser will nourish your plants, the dishwashing detergent helps the solution to stick and also acts as an insecticide, and the baking soda will change the leaf surface pH to alkaline. Fungal mould grows where its host is acidic.

Reproduced with permission from NZOOM Home and Garden content,
from the previous website of  TVNZ News

The views expressed here are not necessarily those of the RNZIH

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Last updated: March 1, 2021