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Home > Plants, Pests & Pest Control > Insects & Pests > Stem and Bulb Nematode

Stem and Bulb Nematode

Garlic bulbs infected with stem and bulb nematode exhibiting symptoms of garlic bloat. Photo by Sandra Jensen, Cornell University, bugwood.org.Scientific name: Ditylenchus dipsaci (Kühn) Filipjev

Native range: Not known

Pest Status

Stem and bulb nematode is not regulated at the state or federal level.


Stem and bulb nematode has been documented in several Minnesota counties but is not considered widespread here. It has a worldwide distribution and is known to occur in a number of U.S. states.


Stem and bulb nematode is a microscopic, worm-like organism. The nematode lives and multiplies within stem and bulb tissue, moving from plant to plant through soil. It is spread to new locations mainly through movement of infected planting material and soil. If hosts become unavailable, once on a site, the nematodes can persist in a resting state in the soil for multiple years until hosts are again available.


Often, plants infested with stem and bulb nematode have swollen and distorted stems and leaves along with rotting stem bases, bulbs, tubers and rhizomes. Garlic plants with this nematode are likely to be stunted with thickened, yellowing leaves and may die prematurely. In early stages of infection bulbs may show light discoloration, which leads to entire bulbs that are shrunken and soft. These bulbs darken and eventually decay. Identifying stem and bulb nematode will require a laboratory test done by the University of Minnesota Plant Disease Clinic.


A number of other problems could cause similar symptoms in garlic. Visit the University of Minnesota’s “What’s wrong with my plant?” website for help in diagnosing issues with garlic.

At Risk

Host Plants and Impact - Many plants are hosts for the stem and bulb nematode, but there are several races of this species, each of which infects different subsets of this host list. The primary concern in Minnesota has been the race that affects garlic.

County-Level Occurrence of Ditylenchus dipsaci in Garlic in Minnesota

To access map legend, click on double arrows in upper left corner. Click on counties for more information.

More Information

What Can I Do?

Stem and bulb nematode is spread to new locations mainly through infected seed. Before planting garlic it is advisable to determine that the source is known to be free from stem and bulb nematode. As an example, the Minnesota Garlic Festival requires that all vendors selling garlic at the festival provide proof of negative tests for stem and bulb nematode in advance of the festival.

The Minnesota Department of Agriculture is monitoring for stem and bulb nematode in vegetable gardens and farms through our urban pathways survey during 2016.

The University of Minnesota Plant Diagnostic Clinic is available to test samples of unknown plant problems.

Contact the Minnesota Department of Agriculture via Arrest the Pest if you suspect you have found stem and bulb nematode. 

Arrest the Pest icon, report sightings by emailing arrest.the.pest@state.mn.us or call 888-545-6684

Last Updated: August 19, 2016