New needles are green (circled in red), and older needles are yellow (circled in blue) on this spruce. Spruce needles that are yellow with no visible fruiting bodies on the needles may be suffering from nutrient deficiency due to constant wet soils this year, or they may have a fungal disease called SNEED (spruce needle drop). Photo by Linda Williams, WI DNR.

In late summer and early fall I had a few calls about younger spruce with yellow needles.  These trees were typically 8-20 years old and were a very yellow color, with new foliage emerging a green color but quickly fading to yellow.  There are two things that came to mind this year.  The first thought is that we’ve had a very wet year.  All year long roots were often in saturated or very moist soil. Consequently. the yellowing could be a sign of nutrient deficiency, specifically nitrogen, due to the saturated soils.  The second possibility is a disease called SNEED (an abbreviation for ‘spruce needle drop’), which I typically see on heavier soils. 

SNEED in spruce is thought to be caused by the fungus Setomalonomma holmii.  Pathogenicity of the fungus has not been proven, but it is the primary fungus present on trees with a particular suite of symptoms.  Spruce with SNEED have current year needles that are a nice green color, but older needles will be yellow or yellow/green in color.  Black fruiting bodies will look like pepper sprinkled generously on the twigs of the affected branches.  Old needles, although not showing any fruiting bodies, will drop from the tree prematurely, and repeated years of this will cause the tree to thin, decline, and can lead to mortality.  I’ve seen this primarily in plantations of white spruce on heavy soils, but have also seen it in blue spruce plantations; it’s reported in Norway spruce as well.  I don’t know of any sure-fire chemical options to prevent infection or to help the trees recover.  Management typically involves removing the most affected trees in the plantation, minimizing stress, and minimizing standing water or waterlogged soils where possible. 

 Written by: Linda Williams, forest health specialist, Woodruff. Linda.Williams@wisconsin.gov; 715-356-5211, x232.

In this photo two oak trees have died from oak wilt (yellow dots). One tree is currently wilting and dropping its leaves (purple dot).

In August, I reported that we’d found oak wilt in Cloverland Township in Vilas County, in Arbor Vitae Township northeast of Woodruff, (on the southern border of Boulder Junction Township), and along Nabish Lake Road in Boulder Junction and Plum Lake Townships.

So, what’s new since then? Another tree killed by oak wilt was identified on the western side of Plum Lake in Plum Lake Township in Vilas County; another tree died in Washington Township just north of the city of Eagle River. I’m still waiting on results from a suspicious tree in northern Three Lakes Township in Oneida County. In many cases spring storms, which occurred during the high-risk period for overland transmission of oak wilt, were to blame for new oak wilt infections. But in some cases, disease was due to logging or pruning that occurred during the high-risk period for overland transmission of oak wilt. It’s important to know where oak wilt is and to minimize your risk.

For more information, visit the DNR oak wilt web page.

Continue reading “Oak wilt continues to be found in the north” →

This oak tree near Pelican Lake dropped leaves due to Cylindrosporium both in 2011 and again this year. This will not cause mortality of the tree.

The small round leaf spots characteristic of infection by Cylindrosporium fungi.

In September and October, I visited several northern red oaks that were dropping leaves, but none of them looked like they had oak wilt. The dropped leaves were still green but had many perfectly round tan dots on their surface. I collected some leaves and sent them into the lab to verify the causal agent. One of these trees had shown similar symptoms in 2011. At that time, Brian Schwingle (who has since taken his forest health skills to the Minnesota DNR) looked at it and diagnosed Cylindrosporium leaf spot. I suspect the same this year. I’ve found trees of all ages with similar leaf spots in Marinette, Oconto, Oneida, Vilas, and Waupaca counties. Impacted trees often dropped some of the infected leaves, although a lot of green leaves (with additional leaf spots) remained on the tree. These trees should leaf out normally next year.

Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.