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