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Tuesday, February 26, 2013

Before You Drop That Bomb...

Some green beans climbing the federation fencing wire. Lush, happy and producing loads of beans.
Let's have a closer look though....

Does the sight of this cause you to gasp and quickly head for the pesticide? 
It certainly does for most people. Even organic growers reach for pyrethrum (because it's safe and natural right?) or some other concoction of rhubarb leaves or tobacco. 
WAIT, can I ask you to spend 10 minutes before you do and really look at the plant and ask yourself a couple of questions first.

There is some leaf damage but there are also more flowers and plenty of beans. The vines seem to be in good health. Healthy plants should tolerate a reasonable amount of attack from pests.
Don't reach for poison just yet.

There are a couple of dead cabbage moths (bottom left) within but I think they have sought shelter here. I bet they have laid their eggs elsewhere. I can't see their eggs hanging from the underside of the leaves or their chubby bright green caterpillars munching away.

I've searched and searched but can't give you a definitive identification of this common garden moth we get here in Tasmania. It is sheltering from the mizzling rain. The moth itself is not a problem but the larvae that hatch are leaf eaters. During my quick inspection I only see two so they are clearly not in outrageous numbers yet.

Here is a green shield bug. Shield bugs make up a large common category and are sap suckers. In great numbers these could definitely ruin your plant. They are easy to spot because they don't particularly hide from predators. They do tend to be a colour that blends with their surroundings but they also have stink glands that secret a foul smelling liquid, hence their other common name of stink bugs. Because of their harder shell, pyrethrum is usually not effective anyway. So hold that spray!

Ahh, the nymph stage (young before adult stage) of the above green shield bug. I am no entomologist but I suspect the colourings are for warning or "foxing" as it probably hasn't developed it's stink glands yet.

This is significant though. I can see six nymph shield bugs in a small space. Numbers are multiplying and definitely could do significant damage but experience has shown me that the plant will take a bit of sap sucking.

Some baby spiders show me that other predators are in the area.
Consider first and remember that spraying a control substance will also kill the predators that are helping you with your problem. Within this vine is probably small frogs and stick insects who also rely on bugs for food.

So standing back and weighing it all up....
The plant has been producing well and I have been picking beans for about six weeks. yes there are some holes and webbing leaf damage but the beans are tender and juicy. Reasonably I can expect another few weeks of picking and I weigh that up with wading in and killing the bugs. What would I gain? Another week or two of cropping? By then the beans are getting tired any way.
The shield bugs perhaps look like they are increasing but natural predation could take care of that within the next week. Given that pyrethrum isn't effective there is no point spraying. My preferred method of control is manual in most cases anyway. In this instance you would use a small brush to move them into a jar or a pair of forceps because remember, they secrete smelly stuff and you don't want that on your hands.

From my experience in the garden, I find the key is to keep things in balance and everything will cycle and take care of itself. 
You definitely DO NOT want to eradicate any one thing.
 Just because it is a pest doesn't mean that it doesn't have a vital part to play. Everything is reliant on something else. It's all part of the cycle  or the chain. Think of yourself as the custodian of the garden rather than the controller. Your job is to aid and assist not to seek and destroy.
I haven't used any sprays in my garden, organic or otherwise in at least 20 years. 
Spend a little time and weigh it all up, including the consequences of wiping out not one but several species. Could you be in fact doing even more harm than a few chewed leaves?


  1. Hey Tanya, your garden is looking lush and green........
    Our beans have been burnt by the sun and haven't done well at far.

    I hope we will get some though, as I love beans fresh from the garden in Summer.
    A great post.....hate those stink bugs. They attack our berries, we pick them off by hand and
    feed them to the chooks. I think they smell like coriander which I love, so I don't mind too much.

    Claire x

  2. In Master Gardeners classes, I've learned to use IPM, or integrated pest management. A first step in IPM is determining your "action threshold," or at what point is a plant really being harmed. Typically, the action threshold is about 30-40 percent. Essentially, about one third of a plant can exhibit insect or disease damage without significantly altering the ability for that plant to produce fruit, flowers, or to return to a vigorous state later on (say, next spring, after the drought, after the bugs molt and move on).
    So, below 30%, keep an eye out. Above 30%, begin managing as specifically as you can for the disease or bug.

    1. Thanks Kat, I knew you would know a thing or two on this and great to have a mathematical guide too. I'll be taking my "action threshold" to our group on Thursday night.

    2. It's a guideline, to be sure. Different plants, different pests, different owners...all these move the 30% up or down. For instance, we have apple maggots in our area, so that's a kill on sight!

  3. i agree with you about 'pest' eradication..i've had a large bird population frequenting my garden this year and they seem to be keeping most of the pests at bay..and i was very happy to see a lovely green praying mantis among my caterpillar chewed up mint the other day..jane

  4. I often use chili garlic spray - my rosellas are getting a little white bug and I got them right before harvesting last time, and they definitely reduced the harvest.

  5. Totally agree!! Yes one of my next posts will be about sprays on food - its really starting to piss me off how the world has shaped our perception of food - how it should look (like in a magazine cause that normal right?) and how it should be grown. Good post :)

  6. The only thing that gets the chop around here are the snails. I'm a snail squasher I'm afraid. I show no mercy to those slimy little critters!

    Such a gorgeous pic of the beans climbing over your fence, sunflowers, hydrangeas etc Tania.

    1. Shame-facedly I must admit to harbouring a desire to "eradicate" snails and I am forced to look at my actions and wonder if I might just take their control a bit too far....Hmmm...perhaps not as they still keep cropping up after a good rain. Thanks Kylie for shining the torch on my sinful corner. LOL

  7. Great post Tanya! I'm like you...I've learned to live with the pests and we still have plenty to harvest.

  8. Wow what a paradise, how beautiful to see and i love all you do here. Wonderful!

  9. Those chubby green cabbage moth caterpillars have turned my sprouting broccoli into green lace. I picked off a dozen the other day and already there were 6 super fat ones back in just a few days. Wretched things. I am tempted to spray as my neighbour has offered me his IPM spray (he says half way between organic and conventional) but since I have 6 measly plants I just wonder if it's worth the effort. After all, with the aid of a tool, bowl and thick gloves (I'm totally grossed out and scared of bugs) I can feed the fat green chompers to my ducks and chooks who love me dearly for my efforts.

    1. My chooks positively trill when I offer them such delights. I am a bit grossed by grubs I must admit but getting a better tolerance level to squish-ness all the time.

  10. I'm with you on this topic Tanya. By the way, here in NZ we call that common garden moth a 'vinehopper' not sure of it's correct name. It lays its eggs on vines like passionfruit - they look like little serrations. Must admit I don't do anything about them, we don't have them in great numbers. The stink/shield bugs though we do, I usually resort to knocking them to the ground and standing on them, but yes the chooks would enjoy them if I could be bothered to collect them. If we ever do need to use any external pest control it's in the form of Diatomaceous Earth.

  11. great post tanya! Gardening Australia seems to constantly advocate "organic" sprays and potions, seems just as bad as using chemicals if you're killing all the insects. The only thing that I have been trying is neem oil, as it only affects the chewing insects and the predators can still get a chance to multiply, but even then, I hardly can be bothered using anything, and the garden does just fine :)

  12. I do try to tread the fine line between blasting all the bugs with pyrethrum, and letting nature take its course. I was very excited to find praying mantis egg cases all around the garden last autumn, and this spring darling miniature praying mantis started popping up everywhere, and our ladybird population is increasing year by year, so I have been careful not to spray pyrethrum on anything but my beleagured hanging baskets this year, and hoping the predators will do their jobs everywhere else.. although I do need something to eat those blasted codling moths..

    I really enjoyed the Better Living Group last night Tanya. You do such a great job finding fascinating speakers, it's so great to be able to pick your brains, and the collected gardening and preserving wisdom of all the members is extraordinary. It's like a gardening brains trust!

    1. You are so lovely Jo. I had a fabulous time last night and I was so sorry Craig missed it. He was very excited with his seed packets from Inspiration Seeds though. I love that quote "gardening brains trust". Our guest speaker from Inspiration Seeds enjoyed the group so much that he intends coming back as a member! A real bonus for us. I will keep you posted about our next guests soon.


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