GARDEN ROUTE NEWS - Dr Jacques van Zyl of the Institute of Plant Sciences, Western Cape Department of Agriculture, shares invaluable tips about nematodes.
Plant-parasitic nematodes or eelworms, are an inconspicuous agricultural pest that negatively influences yield and quality.
It can lead to total crop losses. Plant-parasitic nematodes are very small worm-like animals that can normally be seen only with a microscope. Thousands of different types of nematodes exist and the most widely found in vegetable gardens are the root-knot nematode, followed by the lesion nematode.
The uptake of water and nutrients by nematodes from the plant, leads to above-ground symptoms resembling an element deficiency such as dwarfed growth and yellowing of the plant. Infected plants will wilt during the day, in spite of ample moisture content in the soil.
Underground symptoms on the root that could be visible to the naked eye are:
1. Galls on the roots where the roots are abnormally enlarged due to nematodes feeding.
2. Coarse, discoloured and sunken lesions on the roots.
3. Excessive, hair-like branching of roots.
4. Damaged root tips resulting in limited root growth.
The yield, size and quality of vegetables are negatively affected by plant-parasitic nematodes and high nematode infection levels may even lead to the total destruction of the plant. The presence of root-knot nematodes can easily be detected by the appearance of galls on the roots. Damage caused by nematodes can also be exacerbated by other stress factors like low nutritional status, incorrect pH or drought conditions.
Nematodes can move only a few centimetres per year on their own, but are easily spread by humans and unwashed implements. The use of infected seedlings as planting material will contaminate the soil and will cause an exponential increase in the plant-parasitic nematode populations. Since nematodes are also spread by water, runoff water plays a prominent role in its increase.
All nematode control is preventative; no plant that is infected will react to control because the damage has been done to the plant and is irreversible. One of the cultural practices that can be followed, is positioning the vegetable garden on soil that is free from plant-parasitic nematodes, especially the root-knot nematode.
Crop rotation should be done with a crop that is not susceptible to root-knot nematode and only seedlings that come from a reliable source must be planted since the nematodes can be present in the growth media.
Biological control is promoted by the addition of organic material which helps to suppress the nematode populations by the stimulation of micro-organisms in the soil, of which some are predators of plant-parasitic nematodes.
The planting of resistant varieties of vegetables will also limit yield losses. Solarisation of small land areas through the use of transparent plastic with a thickness of 1-1.5mm during the summer for a period of at least 8 weeks will cause the nematode numbers to drop drastically. Various chemical agents for nematode control are also available from chemical companies.
For more details regarding nematodes, contact Dr van Zyl on 021 808 5302.
Cysts on cabbage roots
Galls on potato roots.
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