Image above showing uninfected carrots (left) and infected carrots (right) 

Image courtesy of: © State of Western Australia
(Department of Primary Industries and Regional Development, WA)

Root-knot Nematodes are transparent soil-dwelling worm-like roundworms that are almost impossible to see with the naked eye. All nematodes are smooth, unsegmented members of the phylum Nematoda - unlike segmented earthworms which are members of the phylum Annelida.

Root-knot Nematodes are members of the nematode genus Meloidogyne. There are many species of this nematode and they are all parasitic on various plants. Some species have specific hosts, while others affect a range of plants. They all have the same modus operandi. They enter a plant’s roots and cause them to form galls or ‘knots’.

Best Treatment for Root-Knot Nematodes

Because Root-knot Nematodes are underground, and because they are so hard to see, you will need to watch for above-ground plant symptoms to detect them. If above-ground symptoms occur you may need to pull up the plant and examine its roots to confirm diagnosis. Check out Symptoms of Root-knot Nematode Damage.

Prevention is the key to controlling Root-knot Nematodes. There are several things that you can do to prevent serious damage from Root-knot Nematodes (see How to Prevent Root-knot Nematodes Appearing).

It is very difficult to completely eradicate any pest, and particularly so with tiny soil-dwelling roundworms like Root-knot Nematodes. The best you can hope for is to suppress them, i.e. ‘manage’ them, and that is why prevention treatments are key.

If you have a regular problem with Root-knot Nematodes you may need to use these prevention methods every year. With Root-knot Nematodes it pays to be persistent. In a nutshell what you need to do is to suppress the numbers, so that any damage they cause is minor or not noticeable.

If infection does occur you will need to destroy all infected plants to prevent infections of other plants.



Image courtesy of: © State of Western Australia
(Department of Primary Industries and Regional Development, WA)



What Are Root-Knot Nematodes and
How To Get Rid Of Them

Root-knot Nematodes are known as ‘endoparasites’, which means they penetrate plant tissue and damage the plant. They are particularly favoured by warm conditions, so they are unlikely to cause problems in southern regions during cool seasons. Various species of Root-knot Nematodes occur throughout Australia.

Root-knot Nematodes invade plants as a second stage juvenile. The immature nematodes release enzymes to soften plant cell walls and a feeding ‘spear’ to create an entry point in plant roots. In response the plant begins producing gall tissue, and roots start to swell. Affected roots have a reduced ability to absorb and transport water and nutrients to the rest of the plant, causing wilting and other symptoms.


Second stage juvenile Root-knot Nematodes are clear worm-like creatures about 0.5 mm long.

Adult male Root-knot Nematodes are about 1 – 2 mm clear, worm-like, and usually rare.

Adult female Root-knot Nematodes are white, spherical (about 1mm diameter), and sedentary within the root gall (knot).

Life Cycle

Female Root-knot Nematodes lay eggs that hatch into first-stage juveniles which remain within the egg case until they moult into second-stage juveniles. These second-stage juveniles move through soil to a root which they enter. Within the root the juvenile moults twice more before becoming an adult – usually female.

Females are sedentary and remain within the root for life. Females can reproduce without males (i.e. parthenogenetically) which is why males are relatively rare. Female can produce about 1000 eggs, and those eggs can remain viable within soil for at least one year.

Root-knot Nematodes complete their life cycle in 4 to 6 weeks in hot weather and about 12 weeks in cool weather.


What Plants Are Impacted by
Root-Knot Nematodes

Root-knot Nematodes are among the most important nematode pests of plants and they have a diverse host range of hundreds of plants including:

  • tomatoes, eggplants and capsicums

  • cucumbers, pumpkins and other cucurbits

  • root vegetables such as carrots, potatoes and sweet potato

  • fruits such as bananas, nectarine, pawpaw and strawberries

  • carnations, chrysanthemums and roses

Symptoms of Root-Knot Nematodes

  • Above-ground symptoms include stunting, wilting and yellowing.

  • Galls up to 10 mm diameter may form on the roots of plants.

  • Carrots may be deformed and covered in galls.

  • Potatoes may be covered in wart-like lumps.


Image above showing infected pumpkin roots

Image courtesy of: © State of Western Australia
(Department of Primary Industries and Regional Development, WA)



How to Prevent Root-Knot Nematodes Appearing


  • Keep an eye out for the above-ground symptoms described. Be particularly vigilant over the hotter months because Root-knot Nematodes are favoured by warm, dry weather.

  • If affected plants have been fed and watered appropriately you may need to look at the plant roots to confirm diagnosis.



  • Practice crop rotation, i.e. don’t grow susceptible plants in the same garden bed every year.

  • Alternate susceptible plants like carrots with less susceptible vegetable crops such as onions.

  • Add lots of compost and other organic matter to soils. This stimulates an increase in naturally occurring soil microorganisms that help suppress nematodes.

  • Plant a green manure crop of mustard and dig it into the garden bed. This releases natural biofumigants known as isothiocyanates which kill the nematodes.

  • Grow resistant tomato varieties such as Yates Tomato Improved Apollo.

  • Check plant roots when transplanting or repotting plants.

  • Don’t put infected plants in the compost.

  • Control weeds. Root-knot nematodes will infect the roots of a number of weeds, especially solanaceous weeds like nightshades.

  • Some websites suggest growing Marigolds as a companion plant with vegetables. This theory is not supported by the scientific literature. However, there is some evidence that growing a trap crop of Marigolds prior to growing vegetables in the same bed may work.

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