Article by: Michael Hillstrom, forest health specialist, Fitchburg. firstname.lastname@example.org, 608-513-7690
Woodpeckers strip bark off tamarack trees infested with eastern larch beetle, causing them to appear red. Photo by Mike Hillstrom
Foresters reported several new areas of tamarack mortality this winter in Marathon and Portage counties. The culprit continues to be eastern larch beetle (ELB). Although historically there have been periodic outbreaks of this native bark beetle, we have seen damage in Wisconsin every year since 1999. ELB initially attack stressed tamarack but, once in a stand, they often sweep through it over a few years even without additional stressors. The droughts of 2012-2013, defoliation by larch casebearer in 2014 and 2017, and prolonged flooding of stands in 2017 were all likely contributors to ELB infestations in central and northern Wisconsin. Infested stands should be salvage harvested and regenerated when possible, given the difficulty of accessing many tamarack stands.
Annual surveys conducted by the Wisconsin Department of Agriculture, Trade, and Consumer Protection (DATCP) indicate gypsy moth populations have increased in several northern Wisconsin counties and by 20% statewide. High moth counts were detected in pheromone traps in Ashland, Bayfield, Burnett (Dewey Township), Iron, Oneida, and Vilas counties, with the highest overall count in Bayfield County (14,354 moths total). Areas with an average catch per trap of 100 moths or more will likely experience damaging levels of defoliation by gypsy moth caterpillars in the following year or years (Fig. 1).
Defoliation can be reliably predicted at the stand level by counting gypsy moth egg masses from August through March before egg hatch; these estimates help determine if preventive measures, such as physical controls, insecticide treatments, or delaying thinning activities are needed until populations collapse.
In recreational and residential high-use areas, physical controls such as sticky bands and burlap barriers may be used to help reduce nuisance and aesthetic impacts from gypsy moths. Aerial treatments are used when gypsy moth populations are high. In managed forests, use of silvicultural techniques may be economically feasible to reduce productivity problems caused by the pest.
Learn more about prevention and management options for your property by consulting with your local DNR forester or regional forest health specialist.
More information about population sampling and management options is available online at www.gypsymoth.wi.gov.
Written by: Paul Cigan, forest health specialist, Hayward. Paul.Cigan@wisconsin.gov; 715-416-4920
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.
A mass emergence of winged ants. Photo by Mike Kamke.
On August 29, and again in early September, a mass emergence of winged ants occurred in southern Vilas County and some areas of northern Oneida County. Mass emergences of winged adults are part of a reproductive strategy used by ants to overwhelm predators, in the hope that a few of the new queens will mate and establish their own nests. When weather conditions are right, winged individuals from many ant colonies in an area will emerge and fly away to mate and start their own nests.
Winged ants consist of large winged females and smaller winged males, but many folks that reported these insects were concerned that they were seeing swarms of wasps since most people aren’t accustomed to seeing ants with wings. Once new queens and males fly away from the nest, they will eventually drop to the ground, shed their wings, mate and start a new nest. These events are relatively rare for folks to see as they are very short lived, with the winged ants generally being gone within a day.
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”
Mature northern red oaks killed by oak wilt in Sawyer County. Photo by Paul Cigan
Late-summer aerial and ground surveys revealed new oak wilt infections within northern red oak stands in Rusk, Sawyer and Washburn counties. Below is an update on the finds in each of the counties.
In Rusk County, aerial detection surveys led to the confirmation of 10 new infections on county forest property. Suspected factors for these infections include spring storm damage and latent detection of past infections caused by logging damage during unrestricted spring harvesting. The county forestry department continues to use cut-stump herbicide treatments to control below-ground transmission. They plan to continue follow-up monitoring of treated pockets and have reported encouraging results to date; only a few pockets treated between 2015 and 2016 contained newly infected oaks on or near the edge of the treatment zone.
Continue reading “Oak wilt update for Rusk, Washburn, and Sawyer counties”
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.
Oak skeletonizer is a tiny caterpillar that feeds on oak by removing just the lower layers of the leaf, leaving the paper-thin upper epidermal layer.
These two pictures are of the same leaf. In this photo, the leaf is being held up to light to show how there is one very thin layer of leaf left where oak skeletonizer was feeding.
Oak skeletonizer (Bucculatrix ainsliella) is a native insect that defoliates oak in Wisconsin. Damage was observed in most counties in northeast and central Wisconsin. There are two generations per year. Damage from the first generation this year barely showed up at all, but defoliation by the second generation became quite noticeable in late August and September. Continue reading “Oak skeletonizer showed up late this season”
Round hard galls from oak bullet gall wasps can impact growth of young oaks if the population is high enough.
There are a lot of galls on oak. One that can cause some problems at heavy densities is the oak bullet gall. These galls, sometimes called rough bullet galls, can quickly become unsightly. I usually see them on burr oak and occasionally on swamp white oak. They are caused by a gall wasp. The galls start out green-colored, eventually darkening to brown as the season progresses and the gall wasp larvae grow inside. Continue reading “Oak bullet gall”
Bronzing along the veins of this oak leaf is due to feeding mites.
In August and September, I observed bronzing due to mites feeding on some young swamp white oaks. The tops of the leaves were very bronzed along the main veins, while the undersides of the leaves remained unaffected. When looking at the leaves with my hand lens and under the microscope, I saw a very heavy infestation of mites. Mites suck plant juices from the cells of the leaf.
Continue reading “Spider mites cause bronzing on oak leaves”