Nematodes

Nematode Damage to Beet (Gerald Holmes, Cal Poly San Luis Obispo, Bugwood.org)

Nematode Damage to Carrots (Washington State University)

Causal Agents

Nematodes are microscopic plant-parasitic roundworms that live in the soil and plant tissues. Root-knot nematodes occur occasionally throughout Utah. They are a cause for concern for root vegetables and ornamental plantings. They can be a threat throughout the growing season but control measures are most effective before or shortly after planting.

Symptoms

Root-knot nematode’s parasitic activity in the carrot causes the root to become forked, distorted, or stunted. This eventually leads to stand and yield reductions. Nematodes feed by releasing chemicals that cause plant cell nuclei to divide without cell division, developing massive feeding cells. These appear as gall formations on the roots. This is a key indicator of root-knot nematode presence. Aboveground, foliage will become chlorotic and stunted. Needle and stubby root nematodes cause similar symptoms in the field.

Disease Cycle

Root-knot nematodes infect plants through the roots. Wormlike, second-stage juveniles (J2) enter the root tip. They migrate in the root until they find a suitable location to establish a feeding site, where they stay for the rest of their lives. They inject hormones that increase nucleus and cell division. The increased cell division causes gall formation. The adult nematode becomes lemon-shaped and eventually breaks through the root/tuber. It produces egg masses that are released into the soil. Stubby root, lesion, and needle nematodes are free-living nematodes. They migrate in the soil and feed on roots, creating wounds that allow other pathogens to enter.

Management

Crop rotation does not help. It is ineffective due to nematodes’ wide host range.
Use cover crops and biofumigation. The mustard ‘Caliente rojo’ can be grown as a cover crop. Incorporate 20 minutes from cutting as a biofumigant.
Till the soil. Till fallow areas once every 3-4 weeks during the hot, dry summer months.
Remove all weeds. Weeds can serve as an alternate host.
Use tolerant or resistant cultivars when available.
Fumigate soil in commercial fields. Products may be difficult to obtain in Utah along with fumigation equipment.
Plant early. Some species of root-knot nematodes found in southern Utah (Meloidogyne incognita and Meloidogyne arenaria) are unable to infect roots at soil temperatures below 50 °F to 64 °F. Consider planting root crops when the temperature is below this level.