Thursday, 17 March 2011

Beneficial Pests

I did not always think of curl grubs as a beneficial pest. I had been told that they could kill lawn and other plants with their appetite for roots. However, it was once I started making huge compost heaps that I realised the information I had been provided was not the complete picture. If you make a compost or have a large pile of manure, once things cool down, the earthworms and other soil animals will move in. This includes curl grubs which help create wonderfully rich soil. So now instead of squishing them, or feeding them to the chooks, when discovered I toss them to the most organically rich spot in the garden. Eat, my pretties, eat!

Understanding why insects are attacking a plant is the best approach in being able to create a healthier garden. Are you starving your soil, thus starving your plants? Have you recently fed your plants high levels of soluble nitrogen? With organic matter and compost in the soil, everything becomes more balanced and stabilised. Root knot nematodes will not be a problem. I can grow tomato plants in the same place for over 6 months and get great crops off them to the end ("the end" being when I need the particular garden plot for something else) with no visible nematode damage to the roots. I do not fertilise the plants during this time either. The reason I can achieve this is that I have made the soil, so incredibly healthy it can support plants for long periods of time thanks to the well fed soil life. I know I have root knot nematodes on the property, as when feral tomatoes come up in the rose garden, their roots have shown signs of attack.

A health plant can respond to trimming of its roots, branches, and leaves, as long as it is in proportion to the health, vigor, and size of the plant. So when an insect arborist wants to ply its trade, who am I to say no? As long as no major or lasting damage is done to the plant or its fruit, then I do not mind. A healthy plant will respond to the trimming by putting out more growth. I have some native trees on the property that get every leaf completely eaten away by a beetle. But the trees always regrow the leaves and power along quite healthily, so why would I spray the bugs with some organic control? There is simply no point.

When I first set up my veggie garden, I left all insects be. I wanted to see what would happen. Would predators come along? Would the pests really be a problem, such that I could not harvest enough for my family's needs? I certainly found that caterpillars are a pest that needs to be managed, thus my current use of Dipel (Bacillus thuringiensis). But this is because I have not set up the right system in the veggie garden with permanent perennials and similar beneficial plants for key predator insects. Thus once garden designs have been changed, it is important to see if the current control methods are still warranted.

Ants are often thought of as a general pest. But they are fantastic recyclers of above surface material including meat. I use ants to pick the fats from bones before I bury them around the garden. Ants can breakdown the fats very quickly, whereas it will take a longer time if immediately buried in the soil. Ants are great predators. Green ants, which I certainly do not appreciate getting bitten by, will easily take down any cut worms roaming your garden. While ants can tend and protect scale and other honeydew producing insects, the presence of these insects often indicates another problem which needs to be managed for the long term health of the plant. Ants can also assist with pollination, for instance sugar ants will pollinate passionfruit and pitaya (dragonfruit).

Ants are also fantastic aerators of soil. My pastures are allowed to grow tall before I harvest the grass for compost, mulch, and other garden uses. The ants love this and build mounds of soil, excavating from below the surface and bringing it to the top. This improves water penetration, helps roots grow, and even sequesters carbon.

There is no doubt that there are pests which are truly just that. Queensland Fruit Fly being a prime example of such a pest. For those starting out in gardening, it can be hard to know what is a good bug, versus a bad one. So it is nice to know that there is a free locally focused website on Brisbane insects called This website is an absolute gem allowing a better understanding of local insects. If you want to see a 28-spotted ladybird (plant eater) versus a three-banded ladybird (insect and/or fungi eater), then this is the site for you. The layout is well done, giving general information and pictures at the top, which allows people to drill down to more insect specific information as identification progresses.

So the next time you see a so-called pest having a go at your plant, ask yourself if nature has simply posted a job opening for a Sanitation Engineer.

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