Root-knot nematodes (Meloidogyne spp) are microscopic worms that live in soil and feed on the roots of many garden crops.
The nematode gets its name from causing swellings or knots on the roots of infected plants. Root-knot nematodes are deadly since farmers can’t easily notice their crops are attacked.
The pathogens are the most common and destructive nematodes. They produce dramatic symptoms and can substantially reduce crop yields.
Root-knot nematodes are found in all agricultural areas and can be difficult to control especially if they survive in weeds.
- The crops, which include tomatoes, potatoes, eggplants, radish or legumes, become stunted, have pale green or yellow leaves and they finally wilt.
- The disease appears in circular patches in a field or garden, but may become uniformly distributed when susceptible plants such as tomatoes are continuously planted in an area.
- Roots have swellings or galls and affected tubers have blisters or swellings.
- Infested potatoes and tomatoes can become more susceptible to bacterial wilt, and symptoms are more severe when plants are also infected with fungal pathogens such as verticillium and rhizoctonia.
Solarisation, which involves tightly placing a clear, plastic cover over the soil and letting it remain in the sun for temperature to rise and kill the pest is one of the effective strategies. For effective solarisation, moisten the soil, then cover it with a clear, plastic material and leave it in place for four to six weeks during the hottest part of the year.
- Nematodes are introduced into new areas by infested soil or plants, thus, avoid moving infected soils to your tomato farm.
- Use only nematode-free plants purchased from reliable nurseries.
- Don’t allow irrigation water from around infested plants to run on your farm as this also spreads nematodes.
- Nematodes can be present in soil attached to tools and equipment used elsewhere, so clean tools thoroughly before using them in your garden.
Chemical control such as fumigation of the soil using nematicides too works well. A number of pesticides or nematicides are available in agrochemical outlets.
They include chemicals such as phenamiphos, dazomet, carbofuran, 1,3-dichloropropene, methyl bromide and ethaprop.
Plant antagonistic crops such as marigold and datura, which produce nematicidal chemicals that kill the nematodes. Also, amend soil with neem cake or green manure of marigold or sunn hemp (Crotolaria Juncea).
Practice crop rotation with non-solanaceous crops that are not affected by nematodes: It may take three to five years to kill the nematodes before replanting the same crops.
Plant certified disease-free transplants: Destroy plants and plant roots by pulling them up immediately after harvest.
Do not let stalks stand after harvesting. Work the soil two to four times during this period, allowing the sun and weather to exert their killing effect.
Soil Amendments: The addition of any organic matter to the garden will improve soil health, and will increase microbial activity in general, which will have the benefit of improving plant health.
Korir is an expert at Soil Sciences Department, Egerton University