Root knot nematodes
Namibian crop pests # 46
Meloidogyne spp. Order: Tylenchidae Family: Meloidogynidae

 

Symptoms on tomato roots

Large galls on tomato roots

Older literature seems to treat all Melidogyne species as one "species" and to call it Root-knot nematode. A better distinction is found in the Crop Protection Compendium CD-Rom, the Global Module (C) CAB International 1999. Until more is known, I will partly follow their description for Meloidogyne incognita, the southern root-knot nematode.
 

Common names: 

 Root knot nematode (English)

Host:

 In practice, most of the commonly grown vegetables are host plants. At Ogongo Agricultural College, we found the worst symptoms of root-knot nematodes on crops such as tomato, Swiss chard and parsley.

Rootcrops such as carrots and beetroot were less infested but even this slight infestation made the product ungainly and unmarketable.

Pest status:

 The major overall pest problem in vegetable production in northern Namibia.

Description:

 The roots start swelling due to nematode infestation and the entire root system is soon  damaged into a lot of galls. Above the ground, plants begin to show wilting symptoms although they are well watered. Nutrient deficiency symtoms are also commonly noticed in for instance Swiss chard due to the destruction of roots. Production of all vegetables is severely reduced and in many cases the plant dies off.

Control:

 There is no easy solution to nematode control. Vegetable growers may consider the following control methods:

Crop hygeine

The build-up of nematodes population is very uneven and they spread only slowly. Pull out or better dig out infested plants with all their roots and destroy them. Plants that are at the end of their production are better dug up and destroyed. 

It is important to clear the field of all galls and root debris which host and protect the nematodes. Do not plant susceptible crops at the worst affected plots. Click here to see an example of how uneven nematode attacks can be.

Crop rotation

Crop rotation has less effect because so many crops are hosts. Avoid growing the badly affected crops such as tomatoes and swiss chard continously on the same land.
Crop rotation with cereals may help reduce nematode population and other pest problems. If our species is the southern root-knot nematode, it seems that rotation with maize or groundnut may have some effect. Otherwise try out Pearl millet. 

Crop rotation with Marigold has been suggested to reduce nematode infestation but do consider that Marigold is a major host for red spider mites and they are even worse than nematodes.

Resistant varieties

Grow nematode-resistant varieties where at all possible. Such varieties are commonly available for tomatoes and they seem to work well. Some of the resistant varieties are very advanced and therefore expensive, however.

Steaming

Steaming under black plastic has been mentioned as efficient for smaller plots such as seedbeds, but I have not tried it. The plot is first watered up to field capacity and then covered with a large sheet of black plastic. The plot is kept covered for two weeks with the plastic until most nematodes have been killed by the heating ("steaming").

Chemical control

Old gardening books often describe fancy fumigation methods against nematodes. Do not use these methods unless you are highly skilled in such operations and have the necessary safety equipment.

If chemical control is found necessary, use the granular forms of nematicides instead and use them according to the safety instructions. At present, mainly Curaterr and Nemacur seems to be used and then only in small quantities in northern Namibia.


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