Issue 4, May 15, 2009
What is Stigmina of Spruce?
Through networking with other plant diagnosticians in the National Plant Diagnostic Network (www.npdn.org) and on a diagnostic listserv, I have been hearing about a "new" fungus found on spruce. Recently we found the fungus on a spruce sample from McHenry County in Illinois. The fungus is Stigmina, most likely Stigmina lautii.
This fungus has been found on spruce trees showing symptoms typical of Rhizosphaera needle cast (issue 2 of this newsletter). When affected needles are incubated, they produce fruiting bodies that look, at first glance, like those of Rhizosphaera. The fruiting bodies of both fungi appear in neat rows on affected needles. This is because the fruiting bodies emerge through stomates. Both fruiting body types are black. Often with Rhizosphaera we see a white waxy cap that has been pushed out with the fruiting body. That is not present with Stigmina. Rhizosphaera fruiting bodies (pycnidia) appear as distinct, rounded, smooth balls. Stigmina fruiting bodies (sporodochia) are loose masses of fungal tissue as seen in the Plant Clinic sample images attached.
We do not yet know whether Stigmina is a pathogen on spruce. We know that this Stigmina is associated with needle blight symptoms on spruce. We also know that there are other Stigmina species that are pathogenic on conifers.
If you would like more information on this fungus, link to this article in "Tree Talk" at North Dakota State University. See the December 2006 issue.
Information at Michigan State University states that chlorothalonil sprays used to control Rhizosphaera needle cast did not control Stigmina. If you have a spruce with a needle cast problem that you cannot control, possibly it is not Rhizosphaera but actually Stigmina.--Nancy Pataky