Getting rid of those plant-sucking insects

When Ooooby-versity started we were asked what subjects we wanted to learn more about. My immediate reaction: aphids.

My fast response time was rewarded by being assigned the task of researching aphids and reporting back to the group.

My learning curve was rapid. I have always thought the word aphid was a generic term for parasitic insects that feed on plants. But in reality aphids are a very particular type of insect, and there are many others that will live on your plants and feed off the sap. Common ones in Auckland include mealy bugs, midges, scale, thrips, mites, leaf hoppers, whitefly, and green vegetable bugs.

And most of these seem to live in my garden. On the bright side, sucking insects don’t seem to be as destructive as slugs or caterpillars which will literally eat a plant to death, whereas the suckers leave ugly deposits, sometimes holes, and stunt growth, but often not much more.

Aphids, according to the information I found, are easy to spot because of their bright colours, ranging from yellow to green to black. They are usually 2-4mm long. Aphids often cluster on young shoots and flower buds or underneath older leaves. Signs that aphids have fed on your plant include: stunting; curls and folds in the leaves; leaf discolouration; dieback or "flagging" of new leaves or newly formed terminals and branch-ends; early leaf drop; ring-like swellings or knots at nodes and buds; and, like most other sucking insects, sooty mould and other deposits – this black soot-like appearance grows thanks to the honeydew excreted by aphids. Ants like to eat the honeydew, so an increase of ant activity can follow sucking insects.

Mealy bugs look like mini slaters with a white fluffy coating. Tell-tale signs on your plants include white fluff on plants and sooty mould.

For the next four suckers, I couldn’t find any accurate descriptions to help identify the insects themselves, but the web is full of information on the damage they do. With midges, look for trails or indentations on leaves as a sign that you’ve got them. Scale leave white patches on stems or pink or brown raised dome-like structures which measure about 3-5mm across on leaves and stalks. Once again, sooty mould means ants have been eating the honeydew scale leaves behind. And scale can also cause death of the plant if the infestation is heavy. Thrips eat the top layer of leaves, causing browning of petals and fruit. Mites make leaves look unhealthy and dusty or speckled. Heavily infested plants may become covered with fine webs, and leaves may dry up and fall off.

Leaf hoppers are a big problem in my Herne Bay garden. These look like brown-grey mini moths, and young leaf hoppers (known properly as nymphs) tend to have tufty tails. Leave hoppers will jump away quickly when disturbed. Signs that they have been sucking your plants include mottling of leaves and black sooty mould fungus.

Whitefly is another one that thrives in my garden. These ones resemble tiny white moths with a wingspan of 3mm. If the plant is disturbed, a cloud of tiny insects fly out but they soon settle back onto the same plant. Damage could include: wilting and stunting of new shoots; silvering and yellowing of leaves; uneven ripening of tomatoes; sooty mould; and sometimes plant death.

Green vegetable bug is easy to spot. It’s a bright green, shield-shaped insect. It can cause: beans to shrivel and become deformed; the kernels of corn shrivel; and on tomatoes and tamarillos hard, corky growths appear where the fruit has been pierced.

How to deal with sucking insects?

You could start with encouraging good predators into your garden. Insects that will eat sucking insects but not damage your vegetables include: ladybird; wasps; the whitefly parasite delphastus; green lacewings; damsel-fly (which looks like a dragonfly); hover flies (they look a little like a small, hovering wasp); and praying mantis. But just how do you encourage these to thrive? None of the books or web sites I consulted had any suggestions.

Companion planting is always a good strategy. Plants that are said to discourage sucking insects include: nasturtiums; pyrethrum; garlic; nettle; basil; and wormwood. Can anyone post a comment on how effective these plants are?

Here are some insect-specific remedies: Squash aphids – sounds like a helluva job, but apparently people enjoy the quiet pleasure of slowly picking off and killing those nasty insects. Pick heavily infested shoots and drop them in bucket of soapy water, which will remove the affected area from your garden and instantly kill the infestation. For leaf hoppers and green vegetable bugs, use derris dust, which is made from plant-root extracts. A word of warning: derris dust is only toxic to fish, so don’t use it if you have a pond. For mites, flowers of sulphur help acidify the soil, which the mites don’t like. For mealy bugs, brush on meths.

Now, according to all the advice, the only sure-fire way to get rid of sucking insects seems to be to spray. And this is something you have to be patient with – multiple and regular spraying will probably be required. All of us Oooobsters want to be organic, of course, so natural sprays that are recommended are: those made of plain soapy water; rhubarb; garlic; pyrethrum; buttermilk; or even plain ice water. I won’t give any specific recipes here, but advise that you Google them and you’ll find instructions for mixing concoctions on the internet.

None of the literature I found during my research mentioned neem oil, though we’ve had some success with it in our garden.

Personally, I’m not totally opposed to chemicals. If I’ve exhausted all other possibilities I would rather hit the pest problem hard and get rid of it, and then have a long withholding period before I eat produce from my garden again. Browsing the internet for information about commercial insecticides aimed at sucking insects, I found most local products to contain diazinon, which has been banned for domestic garden use in the US. Apparently whitefly can build up resistance to sprays, so one company recommended alternating types of sprays.

To end on a slightly defeatist note, it seems to me another problem is that in heavily built-up areas like Auckland’s inner suburbs, even if you rid your garden of sucking insects, there is likely to be a colony in a neighbouring garden and they’ll soon move back in. So maybe a conversation with your neighbours and some advice on how to get rid of their pests would go a long way to protecting your plants. And what’s more, the secret of successful gardeners seems to be to stick at it and keep up a regular programme of spraying alongside your companion planting and other remedies.

Now I’ll be the first to admit that I have never been good at keeping up a good routine in the garden. I have, however, resolved to try some of those natural concoctions, so I’ll keep you posted on progress via the comments to this blog.

(the photo of a ladybird eating an aphid is by the US Agricultural Research Service, sourced via

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Comment by Hester on December 11, 2010 at 7:28pm

I think you've found the key to success Andre.

In my experience minor intervention is best, and working to keep the soil, plants and garden eco system healthy and in balance is the answer. This is not an instant process as it takes time to build up predators but things can change very quickly as you've observed. Especially when predators start going to work, catch crops are used and/or plant life becomes healthier because the needs are being well met. I believe an organic garden needs to have some pests, to be in balance and keep predators in the environment.

I use Neem soap grated into hot water, and given a shake up in an old household spray bottle, then left to cool and used as needed for bad infestations on plants where they  are not wanted.

I believe you can still get Neem soap at the trade aid shop. My 2 original cakes have lasted me years.

Here's a link to some more observations I've written about pest control.


Thanks for researching and sharing such a wealth of information. Great article.

Comment by André Taber on December 11, 2010 at 2:34pm

Well folks, I can report that right now my garden is sucker-free. I tried making garlic and garlic-chilli sprays, but to be honest I found them a hassle and there was no immediate sign of a result. I used a watering can to put them on the vegge and garden beds and low shrubs that had pests. I never got around to neem oil, mainly because it's so hard to find a wind-free moment in Auckland. Then, at an Oooobyversity session, Tony Murrell suggested blasting whitefly off with a hose, so I gave that a go on my citrus trees on two windy evenings. And ever since then, no more whitefly. No sign of leaf hoppers yet this summer either. I have also been a lot more diligent about tending the garden: I gave the camellia, which had some whitefly too, a good prune; and pruned quite a few other plants so there's good air flow through the garden now. I have also been ripping out vegges as soon as they go to seed and generally keeping things tidy. I also gave the lemon and grapfruit trees a dose of citrus fertilliser. And I have been watering regularly; Tony Murrell suggested doing it mid-day to give the plants relief from the afternoon sun. So the garden is generally healthier, but those blasts with the hose probably helped too.

Comment by André Taber on August 27, 2010 at 11:29am
Thanks for those suggestions, Earl. At Oooobyversity we had a short and inconclusive discussion about what soaps are useable on plants and which aren't. Can we assume that Sunlight soap is good? But what else is safe to use?
Comment by Earl Mardle on August 27, 2010 at 9:45am
André, 9 litres is 2 gallons in old money. Marvellous how some things hang on in there.

For what its worth I have a universal spray that I use about every second day through the pest season.

In a 5 litre spray I add
2 tablespoons of baking soda (for moulds and mildews)
A cup of home-made garlic concentrate (bug repellent)
A cup or two of wormwood tea (repels pretty near everything
25 ml of neem oil (to blitz those that don't get the repellent message)
A squirt of liquid soap or detergent to emulsify the oil
Comfrey tea as foliar feed.

Apart from the neem oil there is nothing especially costly there and this year I'm hoping to grow enough chamomile to be able to add some as a further mould/mildew antagonist. Any suggestions for improvement appreciated.

Spraying every couple of days means I also get a close look at almost every plant which helps with other cultivation and management stuff.

As well, pretty much every tomato plant had its own basil bush (and we have enough pesto to last the winter), we also grow a forest of predator attractant and pest repellent plants which, even if they don't work perfectly make the place a real pleasure to be in.

My aim is to have so many companion plants seeding that they become the weeds.

Already we have so many blue borage that we have to pull some out to plant what we need to, but there are plenty more nearby bringing in the bees and building compost content.
Comment by André Taber on August 25, 2010 at 10:20am
I have found a lot of recipes for sprays that include 'summer oil'. Can anyone explain what summer oil is and why it's good for plants?
Comment by André Taber on August 22, 2010 at 3:04pm
OK, I have a quick report on two very simple sprays.

I found several recipes for soap spray on the internet. The consensus seemed to be 225 grams of soap for 9 litres of water. Nine litres? I thought that was weird until I looked at my watering can and discovered it held exactly 9 litres. Must be a standard size.

225 grams equals one-and-a-half blocks of Sunlight soap. So I grated the soap and mixed it with warm water, left it to cool and then watered my insect-infested vege beds with it. Got to the bottom of the can and discovered some of the soap handn't dissolved, so added more water and gave it a good shake and continued watering.

After a few days there seemed to be fewer whiteflies, but I also noticed that the parts of the parsley and celery that had been badly pierced by insects were going very brown. I would assume that if the soapy water gets into the plants it's not particularly good for them.

Then I tried a garlic spray from Brenda Little's book Companion Planting in New Zealand. She says to soak four crushed cloves of garlic in one litre of water. I cut three bulbs of garlic in half, crushed them with the side of the knife and then left them in 10 litres of water for about four days. The result was not particularly strong smelling, but watered onto the affected areas, once again seems to have reduced the numbers of whitefly a bit.
Comment by Tony on August 10, 2010 at 2:17pm
Andre', like any low toxity naturally based pest control Neem Oil should be used as soon as pest insect numbers are observed to rise unusually and as a rule of thumb, if problematic insect populations aren't corrected after 2 or 3 applications of such substances or if the problem keeps reoccurring then it is likely that the problem you are observing is actually just a symptom of an underlying soil, climatic, nutritional or other growing management problem.

More detailed info on NeemAzal TS is available at Commercial quantities only.
Comment by Bonny Faulkner Hollis on August 10, 2010 at 11:14am
Beware of using nicotene, it may cause tabacco mosaic virus? In Tomatoes, we have always stopped people from smoking in the polyhouses.
Comment by Bonny Faulkner Hollis on August 10, 2010 at 11:12am
Also on the subject of Neem we are commercial organic growers and have a number of other commercial growers not just organic using our product for years on a trial basis. We have spent the money and time to get the right mix from India - we have neem oil certified and registered for use on food crops unlike most you can buy off the shelf. We think this should be the break through in New Zealand becoming organic and would appreciate support, with our venture as Yates will pip us at the post if Organics becomes mainstream. Kindest Regards Bonny Hollis
Comment by Bonny Faulkner Hollis on August 10, 2010 at 11:07am
YES!!!!!! NEEM OIL its the underlying secret to your slightly larger pest problems, you cant beat it!
try or call me on 09 4347 429

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