The Inner Gardener

Inner City Gardening for the Soul

Biological Pest Control 16/05/2012


What is a bio-control?  Well, in a nutshell it is a naturally occurring organism that feeds on a population of ‘pests’ in the garden. If you avoid using chemicals in your garden and have a reasonable diversity of plants, then you will probably already have a balanced little eco-system happening. Have you noticed the ladybirds on your roses enjoying the aphids? Have you seen the praying mantis stalking a pesky bug? Even the blackbirds flying in to pick off the caterpillars from the ornamental grapevine are doing their part to control pests.

Some bio-controls are so small that you may not even see them with the naked eye.  A common one sold to control caterpillars is ‘Dipel’ (Bacillus thunbergii). It is a naturally occurring bacteria that comes in powder form, that you mix up and spray on your caterpillar infested plants. The caterpillars start to chew on the sprayed leaf and meet a rather unpleasant end. It is an effective organic control, completely safe for humans and is specific to caterpillars in the moth and butterfly families, so our other ‘good’ bugs are not harmed.

I recently had a black vine weevil (BVW) problem in a client’s front garden. Most of the plants we put in were either ring barked along the stems or had the roots eaten by the black vine weevil larvae. Another typical sign of infestation is the notching along the leaves. The adult does the damage during the night and hides during the day, making them very hard to find and kill. The larvae do the damage to the roots  underground.

Typical BVW ‘notching

More BVW damage

This is one pest where chemicals are fairly ineffective. However, there is a biological enemy of the black vine weevil and it’s larvae,  Entomorpathogenic  Nematodes. (EN’s).  So, I ordered some on-line from a company called Ecogrow – http://www.ecogrow.com.au. This company also supplies commercial quantities to the nursery industry. The nematode concentrate was delivered in a little eski for use as soon as possible (remember they are living organisms).  With full instructions provided, I set about preparing these little warriors for action.

Nematodes in their packaging

All ready to start

I applied the solution with a watering can a couple of weeks ago. The soil temperature needs to be above 12C for them to be effective.  Now, we just have to wait until spring to see if they have done their job of terminating the next generation of BVW. This is the first time I have actively used nematodes as a biological solution and am very interested to see how things go. I suppose one way of telling whether they have worked will be if the surviving plants regenerate in spring. Will keep you posted.

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