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Protecting Your Potato Crop from Nematodes: Identification, Treatment and Prevention

Learn how to identify, treat, and prevent nematode infestations in your potato crop. This guide covers natural and chemical control methods, as well as important safety considerations.

Potatoes are grown all around South Africa, but primarily in Mpumalanga, Limpopo, the Free State and the Western Cape. They are grown commercially, and residentially, in people’s backyards. There are almost 600 potato farmers in the country, providing thousands of potatoes and thousands of jobs. South African potato growers produce over 2.5 million tons of potatoes a year, and the potato industry is an important one. 

Farming is dependent on weather and soil conditions, water availability, political disruptions and pests, and for farmers controlling nematodes can be tricky.


What are nematodes?

Nematodes are microscopic roundworms, often regarded to be the greatest pest in the world, and are around 1.4 mm in length. In South Africa they are particularly dangerous to crops like potatoes that grow underground. 

They can be found in the soil, water and in plant tissues, attacking root systems, significantly affecting the crop itself. In South Africa alone there are more than 450 species of nematode. Left to their own devices, nematodes result in significant yield loss.

The three most common nematodes in South Africa are

  • Meloidogyne spp, root-knot nematodes.
  • Pratylenchus spp, lesion nematodes
  • Globodera rostochiensis, the golden cyst nematode.

Potatoes are vulnerable to these, and to the other nematode species.

What are the symptoms of nematodes?

It is not always easy to recognise nematodes, simply because their action goes on under the ground. Also, the nematodes that feed on plants such as potatoes are so tiny that they cannot be seen with the naked eye. By the time a farmer is aware of the problem, which is described as a population build up, the nematodes are already having a field day. 

Under the microscope, nematodes may resemble the common earthworm. Females, especially when pregnant, may look like beans, but generally, nematodes are long and thin with smooth bodies that are unsegmented. 

It is important for the farmer, or grower, to be aware of symptoms of nematodes, before any significant damage is done, to be aware of pest management.

You will know if your potatoes are being affected by nematodes if they become powdery and brown and if the tuber surface gets dark spots. The surface can also become dry and cracked. Some nematode species cause large lesions in the potatoes that are reddish-brown and even black. It may appear that the potatoes have scabs.

Nematodes spread quickly through movement of soil, water and infested plant materials. Once they are in the soil, it can be hard to eliminate them. 

If you suspect there are nematodes in your soil, you can:-

  • Gently pick a potato plant. 
  • Wash the plant roots, and inspect for damage.
  • If you notice injured roots, root rot, excessive root branching or lesions, you need to find a plan of action.

Nematodes are dangerous not only when the crop is in the ground. Nematodes live inside the tissue of tubers, where they grow at a rapid pace, even once picked and stored. 

Nematode control

Anyone growing potatoes should invest in an integrated pest management (IPM) system. While it might be impossible to rid the soil completely of nematodes, the idea is to ensure there is pest population control. There are a few ways to manage pest elimination and a farmer or food producer should always do their research and use a mixture of strategies. 


Cultural practices

  • Weed on a regular basis. Weeds can serve as food hosts for Nematodes and unwittingly support their reproduction.
  • Add organic matter, to improve soil moisture and to increase nutrients.
  • Till the soil regularly.
  • Add the right manure, peat or compost to increase the level of the good micro-organisms.
  • Cover the soil with specially designed transparent plastic during summer to reduce daytime temperatures.
  • Crop rotation.
  • Host plants, such as rapeseed.
  • Cover crops, including certain grasses such as the Vetiver grass. 
  • Destroy the roots as soon as the crop has been picked.
  • Choose the right chemical crop protection.

Crop protection and soil management are vital. Good soil means a good crop and potato farmers need to check their soil on a regular basis, and keep a check on pests and disease. Potatoes are not only susceptible to nematodes. They are impacted by stem rot, common scab, stem canker, mildew, dry rot, black dot, black scurf, early blight, late blight, various bacterias, tuber moth, leaf miner, bollworm and more! 

Plant protection is a vital part of producing a successful crop. As always, prevention is better than cure, and a farmer should be on top of the different options and strategies to eradicate pests. Many choose to work with crop protection specialists who have a high degree of expertise in this regard. 

What about chemical control of nematodes?

Farmers need to be able to find solutions that will ensure bumper crops in a healthy and ethical way. Some of these solutions may be natural, some are chemical, and often, the solution is a combination of the two. 

Nimitz® is an innovative nematicide developed globally by ADAMA that offers best-in-class performance for the control of root-knot nematodes (Meloidogyne spp). It offers simple, safe and effective application options of the active ingredient – fluensulfone (a heterocyclic fluoroalkenyl sulfone).

Within one hour of contact, nematodes cease feeding. Complete mortality of all active stages of the nematode life cycle is achieved in between 24 and 72 hours, yet beneficial organisms in the soil remain unharmed.

Nimitz® has a “caution” warning (i.e. blue band) on its label meaning it should be treated with respect when handled. It requires less Personal Protective Equipment when compared to organophosphate or carbamate nematicides, which usually have “very toxic” (i.e. red band) on their labels.

Nimitz® has a very favourable toxicological and ecotoxicological profile and is considered non-toxic to birds, bees and aquatic life.

In addition to potatoes, Nimitz® is registered in South Africa for the control of root-knot nematodes for the following crops: 

  • baby marrow, 
  • butternut squash, 
  • melon, 
  • muskmelon, 
  • pumpkin, 
  • gem squash and 
  • tomatoes.


Important to remember

With any chemical, and in terms of ADAMA’s regulations, it is important to always read the label before use. Take note of signal words and hazard statements on the labelling. ADAMA complies with the Regulations Relating to Agriculture Remedies (promulgated on 25 August 2023) under the Fertilisers, Farm Feeds, Agricultural Remedies and Stock Remedies Act, 1947 (Act 36 of 1947).


  • May be harmful if swallowed.

  • May be fatal if swallowed and enters airways.

  • May cause lung damage if swallowed.

  • Causes mild skin irritation.

  • Causes serious eye irritation.

  • Repeated exposure may cause allergic disorders.

  • May cause an allergic skin reaction. Prolonged or frequently repeated skin contact may cause allergic reactions in some individuals.

  • Very toxic to aquatic life with long-lasting effects.

  • Store in a cool, well-ventilated place, away from food and feed.

  • Keep out of reach of children, uninformed persons and animals.

  • Re-entry: Do not enter the treated area until spray deposit has dried unless wearing protective clothing; preferably allow for a 24-hour re-entry period.

ADAMA South Africa (Pty) Ltd
Ground Floor, Simeka House
The Vineyard Office Estate
99 Jip de Jager Drive
Belville, 7530


Nimitz® (reg. no. L10436 Act/Wet 36 of/van 1947) contains fluensulfone (heterocyclic fluoroalkenyl sulfone).