If you notice a plant in your garden that fails to thrive and starts to wilt, the cause could be below ground. Root knot nematode is common in Perth’s sandy, unimproved soil and an invasion of this parasitic pest can cause a plant’s demise. If the plant dies, remove it and look closely at the root system. If there are lumps or ‘knots’ in the fine feeder roots, this indicates the presence of root knot nematodes.

There are many different nematode species living in garden soil. The majority are not harmful and can be beneficial to plants. The dreaded root knot nematode, however, enters the plant’s roots and causes galls or knots to form. These block the movement of water and nutrients through the plant and it begins to wilt.

Plants under stress due to a lack of water or inadequate nutrition plus poor soil structure are more susceptible to root knot nematode damage. Vegetable crops like tomato, beans, capsicum, carrot, and eggplant are common victims of this nematode.

Add Organic Matter

Help your plants fight the pest invasion by adding more organic matter to the soil and watering regularly. A good supply of nutrients and water help plants tolerate any nematode attack. As the organic matter decays, the number of organisms that feed on other soil microbes, including nematodes, increases.

Rotate crops

It is good practice to rotate crops in vegetable gardens. Nematodes will continue to feed on and reproduce in root fragments in the soil. As soon as the crop is harvested, remove the roots to control the nematode population before the next crop is planted.

Some plants, such as Marigolds and Mustard, have been shown to reduce the number of nematodes in the soil. Rotating these plants with productive crops can help control the root knot nematode in the vegetable garden.

Companion planting

Sow mustard seeds densely as green manure and dig it into the soil when it flowers. Keep the soil moist and as the mustard decomposes it will release chemicals that fumigate the soil and reduce nematode numbers.

Two or three months before sowing vegetable crops, plant marigolds into the area. The roots of the marigold produce a chemical that inhibits the hatching of nematode eggs. French marigolds (Tagetes patula) are thought to be effective against a larger range of root knot nematode species than African marigolds (Tagetes erecta).

Please note that this is intended as general information only. Please ask one of our qualified horticulturists for more specific advice for your situation.