Saturday, March 17, 2012

Nematode wars

We've just declared war on nematodes in our garden. This summer we had really poor tomato and silverbeet crops and suspected nematodes. We ripped them up and we were right. In case you didn't know, nematodes are microscopic worms which live in soil.They can enter roots to feed and breed causing galls. If they feed from the outside they cause roots to stunt and distort. They thrive in warm moist sandy soils, which means they are a big problem in Perth. Plants affected by nematodes will struggle to grow and often collapse in the heat because their roots cannot take up water. The only real way to tell whether you have them is by ripping up the plants to look for the distorted roots. Here's a pic of eggplant roots affected.

So, what's the remedy? Well, there are various ways. One is to plant things like mustard, which acts as a soil fumigant to repel them. We did this last year without success. We also added lots of compost and manures to try to improve the soil, but we let the soil dry out a bit and lost a lot of the good bacteria which out compete nematodes. Another way is to use pesticides, but that's obviously a no go for organic growers. You can also solarise the soil. You can do this by putting clear plastic on the soil in sunny weather. This kills off the nematodes (cooks them), but unfortunately it kills all the good bugs that you need in productive soil.

We were getting desperate and were about to solarise. Then we thought we'd make one call before we took this drastic action. We called Derek at our local garden store. Derek knows everything about everything gardening, so it was worth a shot. Of course he knew what to do. He said don't solarise, you'll take one step forward and two back. Instead he suggested a two prong attack. Firstly, buy some molasses and dilute it with 5 parts water and water it on the garden from a watering can. Then add lots of manure, water in well and cover with thick (20-30cm) layers of mulch. We also added vermicompost from our worm farm at this stage.

Wait a couple of weeks and then add a product called Bactivate. It comes in granular form and has lots of bacteria in it, one of which combats nematodes. Apparently the nematodes eat the bacteria, feel very full and starve to death after! You could probably skip the Bactivate if you have lots of compost and vermicompost, but we thought we'd give it a go.

The aim is to introduce as many bacteria into the soil as possible to out compete the nematodes. In this way they should suppress the nematodes whilst doing great things for your soil and plants. The plan is to plant our winter veg after easter. We'll let you know how it goes.

I'm coming to realise that summer is the key season to gardening in Perth. It's so easy to drop the ball in the heat and dry. You tend to plant less and also tend the soil less. If you let your soil dry out over summer you lose all the gains you've made in winter and spring building up your soil and the sand gobbles up all the goodness and you're back to the beginning again. So, next summer I promise to mulch loads more and make sure to keep the soil moist even if there are no plants growing. A green manure would be good too, but I won't get ahead of myself...   


  1. Hi Ads
    What about crop rotation?

    1. Em
      Yes, we do rotate crops but we could get better at it I suppose. It's just that our garden is a bit higgledy piggledy, not with neat, discrete plots. I shall try to do this better though...

  2. Damn, she beat me to it. The work involved in preventing the problem is so much less than dealing with it.

    I miss the challenges of gardening in Perth. How about something that LOVES the hot and dry, like rockmelon or perhaps even watermelon, that will also keep the soil beneath shaded? I reckon there's a lot to be learnt by looking to the mediterranean where they've been doing it for so much longer. Anywhere with a mediterranean climate and has indigenous food plants that grow there during the summer - Israel, California, ...?

  3. Hi guys, found your blog after watching Gardening Australia!
    Love gardening too and always find the Perth summer defeats us when it comes to the garden and we do leave it fallow, rather than trying out things to keep it ticking over.
    Really like your idea of getting a green crop going instead. I thought of experimenting with caper bushes too, as they seem to love the heat and dry. Not sure how they'll go in the winter, but nothing like experimenting hey!
    Will be returning to your informative blog regularly for more tips! Thanks for sharing!

  4. Hi Marg, Summer's really hard in Perth, just remember to keep watering even if you're leaving the vege patch fallow. This way you keep your soil microbes alive and happy.
    Let us know how the caper bushes go. Did you know you can pickle nasturtium seeds and they make a good caper alternative (it's in the River Cottage preserves book). Nasturtiums grow well here in summer, have lovely flowers and shade the soil too.