9 Sep 2014

My bio-diverse garden: Southern Shield Bugs


There's a bookshelf in the design studios at college where unwanted books can be left for others. It was there I found a small pocket sized paperback of Bob Flowerdew's Planting Companions earlier this year. As I garden organically, I do consider Bob one of my gardening heroes. He advises that tomatoes benefit considerably from being grown with asparagus*. After reading it, I thought I was being so clever when I set six of my tomato plants out into ring culture pots within the asparagus bed. As the bed designated for growing asparagus is just one metre square, the crowns are positioned like the dots on a five-dice. The tomato plant pots formed a circle around the central asparagus plant.

As mentioned in my August end of month post, with hindsight, this left them too close together for the fruit to ripen in a timely fashion, until I stripped the lower leaves off. (Although, in a sense, the method does work as I had enormous plants.) By mid-august I noticed that there was a colony of what appeared to be tiny living dots enjoying the warmth at the top of one of the lower trusses. I thought they might be just hatched spiderlings.


See the mottling on the top of the tomatoes? I assume that's bug damage.

I don't mind spiders and they don't do any harm so I left them alone.  As the insects got bigger though I could see that they were, in fact, beetles of some sort.  Time to investigate.

My old friend Google told me that the bugs are Nezara viridula, more commonly known as the Southern Green Shield bug.  These differ from the more alliteratively named Palomena prasina, bugs that do little harm to the garden.  Nezara viridula have arrived in London in the last decade, believed to have travelled over from Africa via Europe, and can be found on tomatoes, raspberries, beans, mallow (Lavatera), Verbena and Caryopteris.  No wonder they're happy in my garden. They also favour allotments; bean growers beware. If handled, however accidentally, they emit a pungent odour.

All shield bugs are sap suckers (not as bad as aphids though) but the Southern Shield bug can cause minor damage to beans, tomatoes, etc by causing the fruit to distort. They're not considered a pest by the RHS as they're most numerous at the end of the season when fruiting is coming to an end.

So what's to be done?  Nothing. (Except (note to future me … ) space your plants out a bit more so that there is more air circulating and less hiding places.) Shield bugs will not do sufficient damage to warrant pest control. The adults overwinter and lay eggs on the underside of leaves in the spring so if you don't want them on your plants, check and remove.  Although that would be a shame as, in my humble opinion, they are all part of the garden's rich tapestry. And rather fascinating to watch.




The science bit: Asparagus roots kill trichodorus, a nematode that attacks tomatoes and in return tomato leaf spray will keep asparagus beetle at bay. Tomatoes also enjoy the company of parsley, basil and nasturtiums and they may be protective of gooseberries.  Certainly my gooseberry bush, growing next door to the tomatoes, appears very healthy. Case closed (for now).


And if there's any doubt:

Southern Green Shield bug


UK native Common Green Shield bug


30 comments:

  1. Fascinating read Caro, one learns something new everyday :)

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  2. *screams and hides self under the stairs*

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    1. But they're only little! Haha, one day they'll grow bigger but green shield bugs are quite pretty. (I also like lily beetles, sssshhhhh!)

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  3. That's interesting, I might try my tomatoes next to the asparagus next year. A shame about those bugs, I hope they don't reappear again next year. And I hope you've still got lots of undamaged fruit. I'm still hoping for some ripening sunshine. CJ xx

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    1. I know the golden rule with asparagus is to let them have a bed all to themselves so I wasn't sure about putting the tomatoes with them. I got round it by growing the tomatoes in large flower shop buckets (99p for 8 from Morrisons) but cut the bottoms out and filled with more compost before I planted the tomatoes into them. It's the ring culture principle of being able to feed the top roots while leaving the lower roots to seek out water and soil nutrients on their own. The plants were super healthy - I hate to think how tall they'd be if they'd had plenty of rainwater! As the fruit ripens, it is beginning to mount up but no gluts this year. Let's hope this gentle sunshine continues for a while! Caro xx

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  4. It's a good year for shield bugs. I found a hawthorn shield bug on the washing the other. It must have been rather lost because the towel was blue and looked nothing like a hawthorn. The real thing is a few yards away ;)

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    1. Now you've got me going! I had to look up hawthorn bug so that if I find any strange bugs in the hedgerows I'll know what it is. I've still to make hawthorn jelly so chances are …. :) Thanks for putting me in the know! C x

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  5. I've seen lots of sheild bugs around just lately but I didn't know of the Southern shield bug, I hope he stays down south and doesn't come and bother us up north.

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    1. Rest assured, Jo, they've only been spotted in the south, so far… ;) I think the Southern Shield bug is supposed to be the most damaging of the two. Also the plain Green Shield bug is native to the UK - and I'm seeing both in the garden this autumn so assume they're not competitive.

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  6. I get green Shield Bugs in my garden from time to time, but never many at once. The business of companion planting has never been very successful for me. I find that the physical aspects are more important than the chemical ones - e.g. will the foliage of one type of plant deprive the other of light or air?

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    1. I was sceptical at first, Mark (especially as the tagetes I planted had no effect on keeping unwanted insects at bay, in fact they made very tasty slug dinners). Because I've studied soil science in my training, I know that plants can put chemicals and nutrients back into the soil via their roots as well as taking nutrients up from the soil so Bob Flowerdew's theories start to make sense. There's a whole world of interaction going on underground, with most plants trying to outcompete each other. Alliums/onions are the worst and I think I may have killed a honeyberry shrub by putting a ring of spring onions around the edge of the pot. Whoooops!

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    2. PS also, of course, the physical aspects are important - right plant, right place and all that!

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  7. Interesting post. I've seen lots of shield bugs lately, mostly on the blackberry bush and having read this I will now look more closely to see which ones they all are. Flighty xx

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    1. Gosh, that's very interesting. I wonder if native shield bugs prefer fruit. Bit more research needed, obviously. Do let me know - perhaps in a blog post? (Actually, I used to find rosemary beetle preferred my mint - until I moved it! Now they've settled back on the rosemary.) C xx

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  8. Very interesting hearing about your companion planting, glad to hear it's working. I've never seen babt shield bugs but do get lots of adults, especially this year. I leave them be too, they never seem to do any harm, I haven't had any on my toms funnily enough.xxx

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    1. Ah, if you're seeing the adults, the babies will be there somewhere. The eggs are laid in spring on the underside of leaves. I wouldn't have noticed these except they all started moving around when I went to pick a ripe tomato - I don't know who moved fastest, them or me!! I think they liked these particular toms as they get a lot of sun on that side. I love having bugs in the garden, I'd worry more if I wasn't seeing any! xx

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  9. Have not heard of or encountered these little creatures ...... yet. Another fan of the Pigtailed One :)

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    1. Maybe you're just far enough north to avoid them, Anna. Certainly London is high on the list of sightings but this is the first year I've really noticed them. I did have a fascinating spider nest once where the babies would regroup into a tight ball every time I went near. Hours of fun watching them! Bob F is a bit special, isn't he!

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    2. PS, I wouldn't mind having his updated book on companion planting but, like you, I'm trying to resist buying books (not very successfully, I admit) so that will have to go on my christmas wishlist :)

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  10. I have no idea about this bug. I have never found like this before. A new lesson for me. Thanks for sharing

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    1. They originated in Africa is my Google research is accurate, Endah. You probably don't have them in your country but I bet you've got plenty of interesting bugs to show us - and probably quite a few that you don't particularly want in your garden!

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  11. That's an invasion - we have only seen a few shield bugs at a time never so many

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    1. I've since realised that I only ever see them when the sun is warming those tomatoes, Sue. They''re all getting bigger so much easier to spot. I rather like them, they look like aboriginal painted ladybirds to me!

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  12. An excellent idea to post a video - and a good idea of the college to have an unwanted book table. I am a great fan of companion planting and Bob too!

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    1. I need a bit more expertise on video posting - the original was a lot clearer! I like the idea of exchange books especially as I have many that I no longer need as I become more confident! I'd love to know more of the science of companion planting as it does seem feasible.

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  13. I've seen loads of the green shield bugs but none of your fancy variety! And what a great find in the "unwanted books" pile...

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    1. Luckily for you Janet,I think that you're too far north! These southern shield bugs are warmth lovers and originate from Africa (allegedly) so perhaps you won't see any. I've never noticed any native green shield babies so perhaps these fancy ones are more eye catching. Rather these than all the spiders that I currently have!

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  14. I've come across these too but never known what they were called and never in sufficient numbers to require anything being done. Our tomatoes this year though are rubbish they all have dark patches like bruises - what can that be due to I wonder. I have cut the dark bits off and the rest is OK but as they are small cherry tomatoes it doesn't leave much!

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    1. The adults can feed on green tomatoes and damage the skin and fruit underneath but the timing is all wrong for them in the UK! The babies don't seem to do much harm - at least so far! I'm intrigued by your 'bruised' tomatoes - I suppose you've ruled out blossom end rot and blight so could be caused by the bizarre weather we've had - dry one minute and torrential downpours the next. The rain caused quite a few of my tomatoes to split and then they got some sort of hideous fungus by the time I found them. There's certainly been a lot to contend with this year!

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  15. A lovely post, Caro. How fabulous to come across those baby shield bugs. Good to hear they don't do too much damage. Have you come across these http://www.field-studies-council.org/publications/fold-out-charts.aspx? We have quite a few and they are great for popping in a bag for easy identification
    when you're outside.

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Caro x

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