Management of root-knot nematode
- Fallow: In areas where climate is characterized by a prolonged and severe hot, dry season, fleaving the fields empty during the dry season followed by growing of non-hosts during the wet season result in significant reductions in Meloidogyne populations.
- Root destruction: Since root-knot can survive and reproduce on the roots left in the soil after harvest, galled roots should be uprooted and destroyed. IThis nematodecan even survive and reproduce in excavated roots and tubers over many weeks.
- Soil Tillage: Repeated tilling and turning of the soil at regular intervals for 30 days during hot and dry seasons between crops reduce root-knot nematode densities in the upper horizons due to desiccation of eggs and juveniles. Tillage also eliminates alternative weed host and volunteer plants from the previous crop.
- Organic amendments: Incorporation of large amounts of organic material (5quintals/hectare) into the soil reduces root knot densities. Oil cakes, coffee husks, neem, marigold leaves, crustacean skeletons, sawdust, urea, chicken manure and bagasse comprise a few examples of organic amendments. Control may be due to:
- toxic compounds present in the organic material as in neem;
- toxic metabolites produced during microbial degradation;
- enhancement of nematode antagonists.
- Organic amendments also improve soil structure and water-holding capacity, reduce diseases and limit weed growth which ultimately leads to a stronger plant and improved tolerance to nematode attack. Neem-based oil cakes and related products have been studied intensely in India for control of root knot nematodes.
- Soil Solarization: The lethal temperature for control of plant parasitic nematodes is considered to be around 45°C. Soil solarization with plastic mulches, which leads to the development of lethal temperatures in the soil, is being used in some countries for control of root knot nematode and soil-borne diseases. The technique is most effective in regions where high levels of solar energy are available for long periods of time.
- Use of healthy planting material: Since early root infection by this nematode leads to severe crop loss, all crop nematode management strategies are useless if transplants are infested with root-knot nematode. Nematode-free seedlings should be selected for transplanting. Nurseries must be free of root-knot nematodes in order to reduce dissemination into root knot-free production areas. Seedbeds should be selected on sites which previously were not planted to host plants.
- Non host crops: Cruciferous crops which are either moderately resistant or tolerant to root knot nematodes are successfully rotated with a smaller number of highly susceptible vegetable crops. Vegetables considered moderately susceptible or tolerant to root knot are cabbage, cauliflower, all cruciferous crops, onion, leek and broccoli. A rotation of cauliflower, garlic and brown sarson (Brassica campestris sub. sp. oleifera) is effective in reducing root-knot densities. A rotation of sesame, maize, groundnut, sorghum, cabbage, velvet bean and then resistant sweet potato is effective in controlling M. incognita.
- Trap crops: In trap cropping, a good host crop is planted for a short duration of time to ensure good nematode penetration and then the developing sedentary juveniles in the root tissue are killed by removal of root from the soil. Lettuce and radish are used as trap crops for root knot management programs at some places. Lettuce is harvested with the shoot and root system intact before the completion of nematode life cycle which usually completes within a month. The roots are discarded before marketing, resulting in trapping and death of large numbers of root-knot juveniles.
- Antagonistic crops: Antagonistic plants are those which produce nematicidal compounds. Marigold, sunhemp, castor-bean, asparagus and sesame are some of important antagonistic crops used for nematode control activity. The best studied antagonistic plant is marigold (Tagetes) known to produce terthienyl and derivatives of bithienyl that are toxic to root knot nematode. Tagetes erecta, grown 2.5 months prior to tomato reduced root knot densities in greenhouses.
- Resistance: Nematode resistant tomato cultivars like PNR 7, Hisar Lalit, Karnataka hybrid, Mangla hybrid etc. have been developed for cultivation in recommended areas. Resistant cultivars should not be grown continuously for years to avoid the emergence of resistance breaking biotypes of the nematode.
- Chemicals: It is important that users realize the stigma of human and environmental toxicity before applying any of the nematicides. Use of nematicides should be preferably confined to nurseries only at recommended doses. Under unavoidable circumstances they may be used under field conditions.
- A number of granular nematicides (phorate @ 1 Kg a.i./ha, carbofuran @ 3 Kg a.i./ha, oxamyl, thionazin, terbufos, isazophos, aldoxycarb, ethoprophos, fenamiphos, cadusafos and avermectins) are effective against root-knot nematodes on vegetable crops under field and green house conditions. Granular nematicides are either broadcast over the soil surface and incorporated into the soil before planting or banded into or over the plant furrow. Liquid formulations allow application by surface and drip irrigation. Application through drip irrigation places the material directly in the rhizosphere and allows treatment at will or treatment when necessary during the growing season. It also allows splitting or extending application over specific time intervals to coincide with optimum control. For example, oxamyl applied to tomato by drip irrigation is more effective than granular nematicides applied at transplanting in controlling root-knot nematodes.
- Dip treatment or treatment of transplants in nurseries is more practical. For example, dip treatment of seedlings of egg plant and tomato with fenamiphos, fensulfothion or carbosulfan @500ppm for 30 minutes or 1000ppm for one hour significantly reduced M. incognita galling.
- Seed dressing of bold seeded vegetable crops like okra, french bean and cucurbits with Carbosulfan 25DS @ 3% a.i. on w/w basis (120g per kg seeds) is effective.
- Biological control: Four approaches are now important for management of root knot nematodes with antagonists in vegetable production:
- Application of fungal pathogens, parasites or predatory fungi that infect eggs, juveniles or adults in the soil or on the root surface. Paecilomyces lilacinus and Pochonia chlamydosporia which are oviparasitic fungi are effective when their commercial formulations are applied @ 50g/m2 along with sufficient quantity of FYM/vermicompost at the time of nursery preparation. FYM/ vermicompost helps in colonization of these fungi.
- Field inoculation and management by using the obligate bacterial parasite Pasteuria penetrans- an obligate parasite of Meloidogyne spp. @ 50g/m2 in nursery or 20kg/ ha in field conditions. The spores formed, can resist both drought and exposure to non-fumigant nematicides. The parasite seems to be more effective on warm soils and soils low in organic matter, which characterizes most tropical soils where root knot is a problem.
- Promotion of the naturally occurring antagonistic potential in soils with amendments or crop rotation.
- Biological enhancement of transplants or planting material with plant health-promoting rhizosphere- or endorhiza-associated bacteria or fungi.
- Quarantine: Quarantine, if practiced, can add greatly by preventing introduction of a pest into a country or local region. In order to protect local production, effective quarantine laws and of course border inspections are needed for nematodes. At the national level, monitoring systems can be used to prevent local spread of nematodes by close scrutiny of commercial vegetable nurseries.
- Integrated Nematode Management: Seedlings may be raised in solarized nursery beds treated with carbofuran @ 0.3 g a.i./h (10 g/m2 ) + neem cake @ 500 Kg/ha in nematode infested soil ten days before transplanting. Soil solarization combined with dazomet gives good control of root knot and increased tomato yield. Similarly, solarization together with carbofuran increased tomato yields by 96% and solarization with neem cake by 52%, coupled with a significant reduction in nematode population. Solarization for 2–4 weeks, combined with fenamiphos is considered a sustainable control measure in greenhouse tomato. Crop rotation and soil incorporation of T. erecta resulted in significant reductions in M. incognita root galling and increased yield.
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