Eelworms
Ditylenchus & Aphelenchoides spp.
also called Nematodes, Stem eelworm, Leaf eelworm
Microscopic nematodes inside stems, leaves, or bulbs causing distorted, stunted growth. There is no cure — destroy affected plants and rest the ground from that host.
How to know it
Invisible: thread-like worms a millimeter long, living inside the plant. You identify them from the pattern of the damage — wedge-shaped dark blotches between the leaf veins on chrysanthemums and ferns, swollen distorted stems on onions and phlox, and concentric brown rings inside an onion cut across.
What you'll see
- Dark, wedge-shaped patches on leaves, sharply bounded by the veins, spreading upward from the base of the plant.
- Stems swollen, soft and distorted, with shortened bloated leaves — "bloat" on onions.
- Brown concentric rings within an onion or a bulb cut in half.
- Phlox with narrow, threadlike, crinkled leaves and split stems.
- Patches in a bed where growth is stunted year after year, whatever you do to feed it.
Where it comes from
Eelworms move in films of water, entering through stomata, wounds and root tips, then feed and breed inside the plant’s tissue. Some survive for years in soil and dry debris as resistant dormant stages, which is why infested ground must be rested rather than treated, and why they travel on seed, bulbs, tools and boots.
Wet seasons and wet soils, and ground cropped repeatedly with the same host. Infected planting material — bulbs, tubers, cuttings — is how it arrives; splashing water and dirty tools are how it spreads.
Dealing with it
- There is no cure and no treatment available to gardeners — accept that and act accordingly.
- Lift and burn affected plants, including the roots and the soil clinging to them.
- Do not compost anything from an infested plant, and clean tools and boots afterwards.
- Rest the ground from that host and its relatives for several years — two is not enough for onion eelworm.
- Water at the base rather than overhead, since leaf eelworms travel in the film of water on the foliage.
Keeping it out
- Buy certified, clean stock — bulbs, tubers, phlox and chrysanthemum cuttings especially.
- Rotate onions, potatoes and beans widely, and never shortcut the rotation on infested ground.
- Control weeds like chickweed and groundsel, which host eelworms between crops.
- Propagate phlox from root cuttings, which are usually free of the stem eelworm.
- Keep the ground well drained; eelworm movement depends on water.
What it goes for
Onions, potatoes, beans, strawberries, phlox, chrysanthemums, ferns and narcissi, each with its own species.
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com