Cool, rainy spring days, nice for ducks and stem nematodes

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Have you ever approached another person in the spring on a cool, rainy day and facetiously said, “Nice day,” and heard them respond with “Yeah, nice day if you’re a duck?” Well, when I’m in that situation, being the nematode geek I am, I think to myself, nice day for stem nematodes. Now, I typically keep these thoughts to myself because if I really did respond by saying out loud, “Yeah, nice day if you’re a stem nematode,” I would expect the other person to swerve a long way from me. I accept the notion that people who work with parasitic worms may frighten ordinary people.

Michigan has experienced average to above average precipitation in 2009. If this trend continues into the spring coupled with cool temperatures, the environment will be ideal for stem nematodes, Ditylenchus dipsaci. Growers of landscape plants should monitor them very closely for symptoms of stem nematode feeding later this spring and into the summer.

Stem nematodes overwinter as fourth-stage juveniles and adults in plant tissue or soil. When moisture is adequate, the nematodes migrate from their overwintering sites onto the stems and leaves of young plants. Maximum activity of these nematodes coincides with the principal growing periods of most hosts, especially annual ones. Females will produce as many as 500 eggs and can live 10 weeks or longer. The life cycle can be completed in three weeks in optimal conditions. These nematodes are very active early in the spring and the production of eggs can commence at temperatures less than 40F.

Symptoms caused by stem nematode infections vary depending on the plant species attacked. Plants propagated by bulbs, corms and tubers are very susceptible to D. dipsaci. This species has a very wide range attacking roughly 500 plant species including many herbaceous perennials. Creeping phlox, Phlox subulata, is very susceptible to stem nematodes and always should be monitored very closely. Severely infested plants often have a hollow appearance, like they are being eaten from the inside out.

Similar to most species of plant-parasitic nematodes, control is difficult to achieve once stem nematodes are established within their hosts. Growers of landscape plants should take steps to avoid these nematodes. This is primarily accomplished by propagating nematode-free plant material and exercising good weed control because many weeds serve as hosts. On sites infested with D. dipsaci, using clean fallow is a good tactic to reduce their population densities.

It is no longer possible to purchase post-plant nematicides for nematode control on nursery plants. Foliar-applied insecticides are reported to provide some control of stem nematodes, but don’t expect these materials to produce 90 percent mortality rates. Plants exhibiting symptoms of stem nematode infections, along with two or three neighboring plants should be dug out and destroyed. Space plants to avoid as much leaf-to-leaf contact as possible.

To avoid stem nematodes or to diagnose problems, plant tissue samples should be sent to MSU Diagnostic Services for nematode analyses. Typically, results will be returned within seven to 14 days. Since all plant-parasitic nematodes are microscopic, submitting samples to a nematode lab is the only way to positively identify these pathogens. For concerns or questions about these or any other types of plant-parasitic nematodes, feel free to contact me (517-432-1333), Angela Tenney (517-353-8563) or Dr. George Bird (517-353-3890). Don’t allow stem nematodes to ruin your day, do your best to avoid them.

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