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Ants and aphids
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Ants and aphids
Hi, I have major numbers of ants in my garden. They appear to be attacking and effecting the growth of small citris trees (peach, grapefruit, manderine)and vegetables (sweet-corn, tomatoes, ...) Is there an organic friendly solution to ant problems in an outdoor garden environment.

Hi Andrew

Is it an ant or an aphid problem?
Usually an ant problem is a symptom of an aphid infestation so check your plants for aphids and by controlling them, reduce the ants’ food source. See below for aphid info and control.

Ant Lifecycle
Egg, larva, pupa and adult. They live and eat differently in each stage. Larvae grow by moulting into pupa and from the pupastage the adult emerge.

There are 35 species of ants in New Zealand. Winged forms occur sometimes.

They have one or two projections connecting the abdomen to the thorax. They have a narrow waist.

A colony consists of queens, winged femailes and males and workers.

A "new" ant, the Argentine ant, was introduced accidentally in 1990 and is found in Auckland to Christchurch. It wipes out native insects abd birds and is pretty aggressive. This ant is a big problem for horticulture. Again you need to establish if you have an ant or tother insect problem. More info about this ant can be found at HortNET. They give information about basically everything within horticulture.

What do they do?
They feed on sugary food such as honeydew produced by aphids, scale, mealy bugs and leafhoppers.

What damage do they do?
Spread diseases very quickly in the garden!

Where do you find ants?
Ant nests are usually found under stones, concrete paths and walls.

What do they feed on?
They will be everywhere where they find sweet sugary foods.

How to avoid them

  • Eliminate food sources
  • Keep it clean everywhere
  • Control aphids, scales, mealy bugs or leafhoppers
  • Destroy nests with boiling water and cracks where they emerge
  • Companion planting such as spearmint, onion and tansy will repel them


If aphids are found ~

Aphid Lifecycle
In spring, over wintering aphid eggs hatch and all are females. Those females will give birth to live nymphs, as many as ten per day. When they reach a number that is too many for the area, some of the females will develop wings and disperse to a new area. Up to 15 generations are produced over spring, summer and autumn. In autumn, some males are produced and they mate with females who in turn lay eggs for over wintering.

The adults are small, 3-4 mm, soft-bodied insects with two projections on the rear end and two long antennae. They can basically be any colour from yellow, green, brown to purple.

What do they do?
Adults and nymphs suck plant juices from leaves, stems and fruit.

What damage do they do?
They cause distorted and stunted growth as well as discolouring and wilting. They are also vectors for virus diseases. They attract ants, bees, wasps and flies because of the production of honeydew. Ants farm them and protect them from predators.

Sooty mould can develop where honeydew is present. Defoliation may also happen if the infestation is heavy.

Where do you find them?
One finds them near growing tips and on the underside of the leaves. Tender shoots.

What do they feed on?
They love brassicas, cucurbits, beans, potatoes, tomatoes, peas, apples… There are several types of aphids who prefer a certain host. So check the colour of the aphid and determine which one it is.

How to avoid them.

  • Wash them off with the hose. However, if you do have ants, they will carry them back. Aren’t they clever!
  • Row covers over new plantings until first flower shows
  • Spray with Neem oil
  • Reflective mulch like an aluminium foil
  • Spray with Pyrethrum
  • Crop rotation to break aphid’s lifecycle by growing food that is not favoured by them.
  • Time of sowing - sow when they are not in flight periods
  • Remove alternative hosts if they are available, such as Shepherds Purse.
  • Non-reflective mulch that reduces contrast between the crop and soil.
  • Only buy healthy plants. Check them thoroughly before taking them home.
  • Spray with Dormant Oil. Apply before buds open. If after buds are open apply it diluted so it doesn’t clog up the respiration for the tree. It will kill the over-wintering eggs.
  • Garlic spray: 3oz chopped garlic bulbs, add 2tsp mineral oil and let it soak for 24 hours. Add 1 pint of water and a ¼ oz soap. Strain it. To use: 1 part mixture with 20 parts water.
  • Rhubarb spray: Boil 3lb rhubarb leaves for 30 minuts in ¾ litire of water. Strain when cold. Dissolve 1 oz soapflakes in ¼ litre of water. Combine the two. Ready to use as a spray for aphids.
  • Soap spray: Dissolve 225 g of plain soap in 9 litres of hot water. Hose the plant with fresh water. Do not use this spray in hot conditions - it will kill the plant because of burning.
  • Stinging nettle spray: Fill a container with as many nettles as you can. Cover them with water. Press them, let them sit for two weeks. Dilute the water until you get a weak tea colour. Add the sludge to the compost.
  • Wormwood spray: Fill a container with fresh wormwood leaves. Add water to cover and let it boil. Let it cool down. Dilute it 1 part mixture and 4 parts water.
  • Companion planting such as chives, garlic, anise, coriander, nasturtiums and petunias will repel aphids. It is said that aphids don’t like the colour orange so it is worth having calendulas and tagetes in the garden as well.

Biological Control

  • Lady Bird Beetles and their larvae
  • Green Lacewings
  • Aphid midges
  • Spiders
  • Assassin Bugs and Soldier Beetles
  • Chalcid and Braconid Wasps lay their eggs on Aphids that hatch into larvae who eat the aphids
  • Aphid parasitising wasp, available from Zonda


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