Twisted, stunted shoots in a spring bulb bed are often the first sign of trouble, and tulips, narcissus and hyacinths can all be affected. The cause is a microscopic worm that lives inside the plant. Getting rid of it means removing infested bulbs and changing how the bed drains, since no quick fix exists for a bulb already infested.
Bulb and Stem Nematodes: What You See
The most telling sign is inside the bulb, so a trowel and a sharp knife help as much as your eyes.
- Cut a suspect bulb crosswise and look for darkened scales that form rings in the cut face.
- Shoots come up twisted, stunted and oddly shaped, often early in the season.
- Leaves look distorted, and the outer scales of the bulb turn brown.
- Bulbs fail to grow or never flower.
- Rot begins in single scales rather than across the whole bulb.
Phlox in the same bed can show similar distortion, which is a useful hint that the problem is spreading beyond the bulbs.
From the almanac
Bulbs in your state
The dates on this page depend on where you live. Your state's page carries its frost dates, its USDA zones and the year laid out month by month.
Northeast
Southeast
- Alabama
- Arkansas
- Delaware
- Florida
- Georgia
- Kentucky
- Louisiana
- Maryland
- Mississippi
- North Carolina
- South Carolina
- Tennessee
- Virginia
- West Virginia
Midwest
Southwest
West
Pacific Northwest
Canada
Bulb and Stem Nematodes or Something Else?
Several bulb problems produce poor, misshapen growth. The difference usually lies in what you find when you dig the bulb up and cut it open.
Looking at the plant above ground is rarely enough, so pair the leaf symptoms with a look at the bulb itself.
| Looks like | How to tell them apart |
|---|---|
| Basal rot on narcissus (bulb rots, plant fails to grow) | Nematode rot starts in individual scales, and the cut bulb shows dark rings, with twisted shoots above ground |
| Viruses on tulips (distorted, poor leaves) | Browned scales and ringed cross sections inside the bulb point to nematodes instead |
Narcissus can also suffer from scorch and lesion nematodes, and tulips from fire and root rot.
What Causes Bulb and Stem Nematodes, and Where It Is Worst
The cause is a nematode in the Ditylenchus genus, a worm too small to see that lives mostly inside the plant, feeding on cells in stems, leaves and bulbs. It infects tulip, narcissus, hyacinth and phlox, and many other crops and weeds can host it, so a weedy bed keeps it going.
It moves in moist, mild weather. In California, young and adult worms travel in a thin film of water on the plant surface, entering through leaf pores when temperatures sit between 59° and 68°F. Egg development is best between 59° and 70°F.
Numbers build fast. In Maryland, symptoms often show early in the season. Rich, wet soil high in humus favors the problem, and no region is singled out beyond that.
How to Treat Bulb and Stem Nematodes
Treatment means removal and a change of conditions, done in this order.
- Dig up a suspect clump carefully, so that you see the bulb and do not scatter infested pieces through the bed.
- Cut a bulb crosswise and look for ringed, darkened scales, so that you know the cause before you pull healthy neighbors.
- Remove every infested plant, because the worms live inside the tissue and will move on to nearby bulbs.
- Bag the bulbs and soil clinging to them and send them out with household trash, so that infested tissue does not return to the garden.
- Rework the bed to drain well, since rich, wet soil with a lot of humus favors the nematodes.
- Call your state extension office if the diagnosis is unclear, so that a lab can confirm what is in the bulb.
Treatment choices and any registered products depend on your state, so that office is the place to ask. Leave healthy plants alone and let their leaves yellow naturally, since green foliage is still feeding next year’s bulb.
How to Prevent Bulb and Stem Nematodes Coming Back
Prevention follows the bulb year, with a few checks timed to the season.
- In early spring, watch shoots as they emerge and pull any that look twisted or stunted before the worms spread.
- As the weather turns mild and damp in spring, keep the bed from staying soggy, since moisture on leaves lets nematodes travel.
- After flowering, pull weeds and nearby phlox that look distorted, because they can carry the nematode between seasons.
- When you dig or divide bulbs in summer, discard any with browned scales or rot confined to single scales.
- Before planting in fall, choose a spot with well-drained soil and avoid rich, wet ground with a high humus content.
Bulbs that are still unplanted go into the ground as soon as the soil can be dug, in a bed that has passed these checks.
Where This Comes From
The facts here come from university extension and government plant health pages, including notes written for Maryland and California. Timing and temperature details hold where they were written, so check them with your state’s extension service before you act.
Common Questions
Can You See Bulb and Stem Nematodes Without a Microscope?
No. The worms are too small to see, and what you notice is the damage: twisted shoots, browned scales and ringed cross sections inside the bulb. A lab can confirm the cause if the signs are unclear.
Can a Bulb Look Healthy and Still Be Infested?
It can. Rot starts confined to individual scales, so the outside may look sound while the inside is already darkened. Cutting a doubtful bulb open tells you far more than its outer skin.
Should You Replant Bulbs in the Same Spot?
Remove all infested plants first, and avoid planting again in rich, wet soil with high humus. Whether to wait or switch plants depends on local conditions, so ask your state’s extension service.