Common garden pests and how to kill them

Many gardeners will use spray as their main weapon in the war against pests.

Many gardeners will use spray as their main weapon in the war against pests.

Many garden insects do no harm at all and some – the beneficial insects – are garden superheroes. But if you find yourself on the receiving end of plant-assassinating bugs, you'll likely employ any method to get rid of them.

If left unchecked, scale, stink bugs and even millipedes can do some damage in the garden.

Centipedes vs millipedes? Not sure which is which? Next time you see a bug that has lots of legs, take a closer look. Millipedes have two pairs of legs from each body segment, while centipedes have only one pair per segment. The body of centipedes is also fairly flat, while the millipede's is more rounded.

Scale insects infest a camellia tree.
Vicki Price

Scale insects infest a camellia tree.

Millipedes feed mostly on decaying plant material, although they sometimes take a fancy to young seedlings. When they do, they'll eat the leaves, stems and roots. Centipedes are carnivorous and feed on insects and spiders.

An overabundance of millipedes can be a nuisance, but they are easy to control, without chemical warfare. They like moist environments, so remove any rotting leaves, wood and other kinds of moist, decaying plant matter, or anything where moisture can collect. They will not survive long in dry conditions without any food.

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Scale may be your nemesis, but there are all sorts of scale insects.

Adult passionvine hopper with the "fluffy" nymphs. A pyrethrum spray may be the best hope of ridding your plants of this ...
Supplied

Adult passionvine hopper with the "fluffy" nymphs. A pyrethrum spray may be the best hope of ridding your plants of this common pest.

Have you those strange white blobs on the undersides of your hydrangea leaves? These are the waxy egg masses of cottony hydrangea scale (Pulvinaria hydrangeae). First recorded in New Zealand in 1977, the young nymphs hatch from midsummer and suck sap from the undersides of leaves. They move to the stems in late summer where they overwinter before maturing in late spring. Severe infestations will weaken plants.

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Now is as good a time as any to peer beneath your bushes for signs of them. If you see them, remove the leaves and bin them.

If you'd rather spray, the best time to do so is when the nymphs hatch (there is only one generation a year) from midsummer. You will need to spray several times to ensure you target the nymphs as they hatch. A pyrethrum-based spray works when newly hatched; if spraying in autumn, use a mineral oil spray.

There is another scale that looks similar to the cottony hydrangea scale and that's the soft wax scale (Ceroplastes destructor) – a serious pest on citrus and sometimes kiwifruit.

As above, there is only one generation a year, and they suck the sap from plants and can severely weaken them if numbers are high. Use an oil spray to control them.

Research from a trial at Kerikeri found that the best time to control them is around mid-January to mid-February, when the new generation is produced, though you can still spray them now. Make sure you spray on the undersides of the leaves as well as the stems for good coverage. It may take a couple of seasons to control them completely.

Flax bushes are not immune to scale either. Large infestations of flax scale, which looks a bit like mealy bug – white and woolly – can be very damaging to plants. They suck the sap of leaves and weaken them, making them susceptible to disease. Stressed plants seem to attract more scale.

The young scale insects are very active and can be blown from plant to plant by the wind, so they can get around quite quickly.

They are protected by their cottony surrounding, their shell and the fact that they tend to hide where the leaves sheath together at the bottom of the fan and on the rhizome – places that are hard to spray.

If you use oil sprays, make sure you spray several times – every two to three weeks – until you get on top of the problem. Let the oil run down the leaf sheaths and bases to get to the scale that you cannot see. You could also try a systemic spray; as the scale sucks the sap they will ingest the insecticide.

The green vegetable bug, aka stink bug, is common in gardens throughout New Zealand. They suck the sap from summer vegetables and ornamental garden plants, which can result in deformed shoots and fruit and flower drop. The young, wingless nymphs range in colour from green, brown or black, with orange, red or white markings. You can use a pyrethrum-based spray to control them; spray in the morning or evening when they are least active.

Invaded by passionvine hoppers? The lacewing adults are tricky to control as they flit off when they see you coming. Give them a blast with a pyrethrum-based spray.

If numbers are high you'll need to spray continuously throughout the season, and probably the next two, until you get on top of them.

Whatever bug you may have, if you get on top of it when first sighted, you'll go a long way to controlling the numbers before they build up.

* Visit Jane's blogs: sweetlivingmagazine.co.nz and flamingpetal.co.nz

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