Cause Meloidogyne hapla, a nematode that also attacks other vegetable crops. The Columbia root-knot nematode, M. chitwoodi, is not an economic problem on carrots. Root-knot nematodes are sedentary endoparasites; only second-stage juveniles (the infective state) and adult males (which may be rare) are in the soil. Northern root-knot nematodes are very damaging to carrot, and the tolerance is very low, so proper nematode sampling is essential.
Symptoms Localized areas of stunted plants. Infected carrots are typically forked and malformed. Numerous knots can be found on the tap root and secondary roots. When carrots are left in the soil for long periods in fall and winter, nematodes often enter lenticel areas and cause large galls.
Sampling Before planting, take soil samples with sufficient lead time to implement management procedures if necessary. For example, after soil fumigation, it may be several weeks before crops can be seeded. Fall sampling for planting in the following spring is an excellent strategy. When sending samples to diagnose a suspected root-knot problem, it is best to include carrots and roots as well as soil.
- Rotation with a non-host such as corn or cereals is excellent because they rarely are injured by this nematode.
- Avoid irrigating from ponds in which water from infested fields has drained.
- For infested home gardens, interplanting or rotating with marigolds will help to suppress populations.
Chemical control Preplant soil fumigation.
- Telone II preplant soil fumigation. Allow 2 to 3 weeks between application and planting or until odor has left soil. Do not treat extremely heavy soils. Considered a nonfood use. 5-day reentry. Restricted-use pesticide.
- Vapam HL at 37.5 to 75 gal/A. See label for guidelines on rate, application conditions and methods. 48-hr reentry. Restricted-use pesticide.
- Vydate L in-furrow at planting at 1 gal/A or through chemigation at 1 to 2 gal/A. To prevent damage to seeding plants, apply after planting before or just at crop emergence. A second application 14 to 21 days later will extend the period of plant protection. Application programs that start after crop emergence may not be as effective because damage may have already occurred. Subsequent applications can also be made during the growing season if nematode damage is observed. When applying via overhead sprinkler chemigation, limit the amount of irrigation water so that the Vydate L treatment is concentrated in the carrot root zone. Do not apply more than 4 gallons per acre per crop and do not apply sooner than 14 day prior to harvest. 48-hr reentry. Restricted-use pesticide.
- MeloCon WG at 2 to 4 lb/A at 4- to 6-week intervals for nematode suppression. See label for specific application types and timings. O
References Becker, J.O., Ploeg, A., and Nunez, J.J. 2019. Multi-Year field evaluation of fluorinated 21 nematicides against Meloidogyne incognita in carrots. Plant Disease 103:2392-2396.
Santo, G.S., Mojtahedi, H., and Wilson, J.H. 1988. Host-parasite relationship of carrot cultivars and Meloidogyne chitwoodi races and M. hapla. Journal of Nematology 20:555-564.
Walters, S.A., and Barker, K.R. 1994. Current distribution of five major Meloidogyne species in the United States. Plant Disease 78:772-774.