Managing Root-Knot Nematodes in Tomato Gardens

Root-knot nematodes are microscopic worms that invade tomato roots, causing galls that impede water and nutrient uptake. Plants survive but yield poorly. No chemical nematicides are available for home gardens, but cultural tactics can reduce damage.

Two Effective Strategies

1. Winter Tilling: Till the planting area in January. Cold temperatures and wind exposure kill many nematodes.
2. Clean Soil Planting Holes: In April, dig 16-inch-wide holes for each tomato and fill with bagged, nematode-free planting mix. This gives roots a head start in clean soil. By the time roots reach infested native soil, plants are large enough to produce a good crop before severe damage occurs.

Marigolds: Limited Help

French marigolds (Tagetes patula varieties ‘Tangerine’, ‘Petite Harmony’, ‘Petite Gold’) can suppress nematodes if planted as a solid block 7 inches apart with no other roots present. They trap nematodes in their roots. Rotate marigolds and vegetables yearly. Effectiveness is modest compared to the two methods above.

Root-knot nematode galls on tomato roots.

French marigolds planted densely for nematode suppression.

Tomato grown in clean soil hole outperforms nematode-infested neighbors.