Lesion nematode identification & organic treatment
Pratylenchus spp.
How to identify lesion nematode
A migratory soilborne roundworm that tunnels through roots (rather than settling in one spot like root-knot nematode), leaving dead, discolored lesions that open the door to fungal and bacterial rot organisms.
Symptoms
- Small, dark brown-to-black lesions on roots that can merge into larger dead patches
- Stunted, patchy above-ground growth, often in irregular patches across a bed rather than uniformly
- Reduced root mass and poor nutrient/water uptake mimicking drought stress
- Increased susceptibility to soilborne fungal root rots at the lesion sites
Host crops
Potato, Carrot, Strawberry, Apple.
How it spreads
Moves through the soil and enters/exits roots repeatedly (unlike root-knot, it doesn't stay put); spreads on contaminated soil, tools, and infected transplants/tubers.
Favorable conditions
Cooler soil than root-knot nematode tolerates, moderate soil moisture; populations build over successive susceptible plantings.
Progression
- Root tunneling (Throughout the growing season) — Nematodes migrate in and out of root tissue, feeding as they go.
- Lesion development (Following tunneling) — Dead, discolored lesions form where feeding occurred.
- Secondary rot and decline (As lesions accumulate) — Fungal/bacterial organisms invade lesion sites, worsening root loss.
Organic treatment for lesion nematode
- 1. Rotate to non-host cover crops · medium effort
Plant marigold, cereal rye, or other non-host/suppressive cover crops for a full season before replanting susceptible crops.
When: Off-season rotation
- 2. Improve soil health with organic matter · low effort
Add compost to support beneficial soil organisms (predatory nematodes, nematode-trapping fungi) that help suppress populations.
When: Ongoing
Prevention
- Rotate susceptible crops with resistant grains or non-host cover crops for 2+ years.
- Use certified nematode-free seed potatoes and transplants.
- Clean soil from tools and equipment between beds.
Easy to confuse with
Root-knot nematode (produces swollen galls, not lesions), General soilborne root rot without a nematode present.