Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Carrot (Daucus carota) -- Nematode (Root-knot)
 
Cause: Meloidogyne hapla, a nematode that also attacks other vege-table crops. The Columbia root-knot nematode, M. chitwoodi, is not an economic problem on carrots. Root-knot nematodes are sedentary endoparasites (see Nematodes); 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.

Note the swellings on the fine roots.

 
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.
Cultural control:
  1. Crop rotation with a nonhost such as corn or cereals is excellent because they rarely are injured by this nematode.
  2. Avoid irrigating from ponds in which water from infested fields has drained.
  3. For infested home gardens, interplanting or rotating with marigolds will help to suppress populations.
Chemical control:
  1. Telone II preplant soil fumigation. Restricted-use pesticide. 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.
  2. Vapam HL at 37.5 to 75 gal/A. See label for guidelines on rate, application conditions & methods. 48-hr reentry.
  3. 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 protec-tion. 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 irrrigation 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. Restricted-use pesticide. 48-hr reentry.
References:
Walters, SA. and Barker, KR. 1994. Current distribution of five major Meloidogyne species in the United States. Plant Disease 78:772-774.

Santo, GS., Mojtahedi, H. and Wilson, JH. 1988. Host-parasite relationship of carrot cultivars and Meloidogyne chitwoodi races and M. hapla. Journal of Hematology 20:555-564.
Content edited by: Russ Ingham and Cynthia M. Ocamb on January 1, 2010
 
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