Forest Insect and Disease Newsletter


Round-up of those dad-burn, pesky varmits


2012 Aerial detection survey maps

Aerial detection flights were flown from June to late August this year by DNR Resource Assessment and USFS, S&PF. Please note that polygons are buffered and appear larger so that you can see the small ones more easily.


image:  Forest tent caterpillar: Defoliation

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Forest tent caterpillar: Defoliation - Aspen, basswood, oak, birch

274,600 acres

Trend is increasing; up from 61,000 acres

image:  Larch beetle aerail detection survey map

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Larch beetle:

Mortality - Tamarack
42,200 acres of new mortality
Trend is increasing; up from 17,000 acres

image:  Spruce budworm aerial detection survey map

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Spruce budworm: Defoliation - Balsam fir, white spruce
82,770 acres
Trend is decreasing acres, but new in Cook Co.

image:  Spruce budworm-mortality aerial detection survey map

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Spruce budworm:

Mortality - Balsam fir, white spruce
79,200 acres
Trend is decreasing

image:  Larch casebearer aerial detection survey map

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Larch casebearer: Defoliation - Tamarack 18,400 acres
Trend is increasing; up from 11,000 acres

image:  Two-lined chestnut borer aerial detection survey map

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Two-lined chestnut borer: Mortality - Oaks
1,200 acres
Trend is increasing; up from 59 acres

image:  Aspen decline aerial detection survey map

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Aspen decline:
Dieback and mortality - Aspen
89,800 acres
Trend is increasing; up from 57,000 acres

image:  Ash decline aerial detection survey map

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Ash decline:
Dieback and mortality - Ash
23,100 acres
Trend is static

image:  Dutch Elm disease aerial detection map

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Dutch elm disease: Mortality - Elms
3,000 acres
Trend is increasing; up from 480 acres

image:  Wind damage aerial detection survey map

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Wind damage:
Stem breakage and mortality- All species 15,800 acres
Trend is decreasing; down from 25,400 ac


Forest tent caterpillar populations are building


A native defoliator of hardwoods, especially aspen, basswood, oak, birch, and willow, forest tent caterpillar (FT) populations peak every 10 to 16 years in Minnesota. And looking at the chart below, it looks like these populations could be building toward a 2014 or 2015 peak.

Acres defoliated by forest tent caterpillar 1985-2012

This summer, 274,000 acres of defoliation were mapped during the aerial detection survey. Notes about FTC:

image:  Forest tent caterpillar populations in 2012 aerial map

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  • From Beltrami and Lake of the Woods Counties to Cook County, aerial survey was delayed by two months and very few acres with FTC were mapped, so we really don't know how extensive FTC populations were. We'll have to wait until next year to fill in this gap.
  • A dozen 60-acre pockets of defoliation were mapped in Fillmore and Houston Counties; a rare occurrence for this area.
  • Far from declining, the FTC populations in west-central counties are going strong. There basswood and oaks are the primary targets and both species might be in trouble of declining in 2013 due to the duration of the local outbreaks.

FTC in Cass CountySpeaking of big acreages of defoliation, Cass Co. had the three largest polygons this year: 14,113; 6671; and 5975 acres. Which county will be the lucky winner next year?

Eastern larch beetle acres more than double this year

image:  Tamarack mortality for 2000-2012

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Tamarck mortality from 200-2012

Again this year, the bulk of the tamarack mortality occurred in extreme northwestern counties (see map). The new wrinkle was the number of acre lost this year–42,275 acres–2.4 times the acreage lost last year (see chart below). Quite a jump! Was this an unusually bad year for tamarack survival? Did the larch beetle population switch from one generation per year to two generations per year? Was the timing of our detection survey much better than last year? That remains to be seen, so stay tuned.


Acres of new tamarck mortality by year graph

Tamarack Assessment Project

Tamarack is an important component of Minnesota's forests. At the time of European settlement, tamarack was the most abundant tree in the state (16.9 percent of the state's original bearing trees). Tamarack has declined more than that of any other tree species in Minnesota, in response to exotic and native insects, logging, agriculture, and settlement. In 2011, the tamarack cover type represented only 3.8 percent of all trees in the state's Forest Inventory and Analysis (FIA) system. The tamarack resource has been undergoing major mortality for the past ten years due to eastern larch beetles. In addition, mortality in the tamarack resource appears to be accelerating over the last decade. A number of factors are likely contributing to the current mortality.

A team has been formed to analyze the tamarack resource and produce recommendations on what the Minnesota DNR needs to do to best manage this resource in light of a variety of forest health, forest product market and budget challenges. The team consists of representatives from the forest health, silviculture, ECS, utilization & marketing, timber sales and resource assessment programs, and a wildlife manager and field forester from an Area with a significant tamarack resource. By November 30, 2012, the team will produce a report indicating resource condition, likely outlook, and recommended actions for management.

Spruce budworm defoliates conifers in Cook County

A surprising turn of events was found in the aerial survey this year: spruce budworm caused recordable defoliation in Cook County. These areas are well outside the existing areas in St. Louis and southern Lake Counties where it has been working for the last few years. No mortality was noted.

Spruce budworm in St. Louis County

Spruce budworm- St. Louis County

Spruce budworm- Cook County

Spruce budworm- Cook County

Rose chafer beetleRose chafers

There have been a number of complaints of rose chafers in the Grand Rapids area. Rose chafers are a small beetle about 3/8-inch long and appear ungainly because of their long legs. They have a straw or tan colored body that gets darker with age as hairs on the wing covers and thorax wear off.

Rose chafers get their name because they are frequently found on roses, and they can also be found feeding on flowers peonies. They damage fruits of grape, raspberry, and strawberry, and skeletonize leaves of trees and shrubs, leaving only the main veins uneaten.

The adults prefer to lay eggs in sandy soils. The larvae are grubs that feed on roots of grasses and weeds. Adults become active in late May to early June and live four to six weeks. There is a single generation per year.

Japanese beetleRose chafers can be difficult to manage and control. Small numbers of beetles can be hand-picked and killed in a container of soapy water. There have been reports that the beetles fight back with their long legs and grab you when you try to squash them, so be safe out there and always remember to use the proper bug-squashing techniques. More information on control options are found on the University of Minnesota Extension.

Bamboozled by bugs

We had some pretty interesting reports this summer from folks bothered by tiny livestock. In the middle of May, there were reports in Pine Co. and Kanabec Co. of large numbers of beetles feeding on cherry tree leaves. They turned out to be blister beetles, probably Lytta sayi (no common name). These beetles are elongate and iridescent green with orange legs, and can be up to ¾-inch long. Blister beetles are so-named because they contain a substance called cantharadin that can cause blisters on contact with human skin. Fortunately, this species does not contain enough cantharadin to be a problem. Find Lytta sayi also feeding on lupine, hawthorn and juneberry.

Lytta sayi- Blister Beetle

Blister beetle Blister beetle

Another mysterious critter required careful watching by a homeowner in order to identify it. The homeowner sent the photo below of a cocoon found in storm window tracks. The cocoon was surrounded by grass, adding to the mystery.

Once the adult emerged, the homeowner sent the specimen to us, and we were able to identify it as a grass-carrying wasp. These curious insects line their nests with blades of grass. They often choose artificial cavities, such as window tracks, in which to build their nests. The female stocks the nest with a tree cricket she has paralyzed and lays her eggs on the tree cricket. Once her larvae hatch, they feed upon the paralyzed but living cricket. The adult wasps can sting if handled, they are not aggressive and do not defend their nests.

Grass-carrying wasp

wasp Wasp nest

No silver bullet for rough bullet gall

Rough bullet galls on Oak twigRough bullet galls on bur oak seedlings have been a common problem west of Bemidji for the last few years. Jeff Hahn, University of Minnesota Extension Entomologist, was contacted regarding possible control techniques. He replied, "These galls have the potential to reduce the attractiveness of a young tree by altering the branch structure, although normally the health of the tree is not affected". It is also possible that severely infested trees could be sufficiently weakened, and with the added stress of being recently transplanted, they could die. As trees become established, this kind of infestation does not threaten its health.

"Treatment is very challenging. In fact, I do not encourage people to try to use insecticides, because treatments in general are ineffective. There is not a lot of research looking into how to treat these types of galls".

What to do? About the only thing left is to foster rapid seedling establishment and growth, thereby minimizing the time young oaks spend being vulnerable to gall wasps.

For more information on this gall wasp, see the June 2012 issue.

Dook’s needle blight of white pine

Needle blight of white pineIn the mid- and late-1990's we mapped a needle blight of white pine in a broad swath from Duluth to Bagley ("White pine needle blight: all that glitters isn't gold." I&D Newsletter, Aug. 1998). The fungus was described in the US as Canavirgella banfieldii in 1986. A similar fungus was described in Canada as Lophophacidium dooksii in 1984. This year a Canadian mycologist, Gaston Laflamme, confirmed that they are one and the same fungus, and the name will be L. dooksii, or Dook's needle blight, since that name takes precedence in the literature.

Why bother with that now? An outbreak of Dook's in the white pine blister rust-breeding orchards in Ontario is affecting several five-needled pines. The current year's needles are killed, and if heavy infection occurs, there can be growth losses. As it turns out, Macedonian pine, Pinus peuce, is being bred with eastern white pine to increase white pine blister rust resistance. Unfortunately, P. peuce is highly susceptible to needle blight (average, 57 percent infection). White pine has low susceptibility (13 percent) and hybrids are intermediate (42 percent). So while breeding for WPBR resistance, gene(s) for susceptibility to a North American needle disease in non-native pines were also inadvertently bred into the white pine hybrids. Canadian pathologists are calling this a "cryptic invasion" by the susceptible gene(s) for Dook's into the white pine breeding program. How they deal with this invasion is yet to be determined

Ink spot and shot hole disease on trembling aspen

ink spot on trembling aspenThis picture of aspen leaves with ink spot disease was taken from roadside trees near Rutledge in Pine County. The fungus that causes ink spot kills the leaves in late spring and produces a black fruiting body or ink spot on the brown leaf that stays hanging on the tree. Later in the summer, the fruiting body falls out of the dead leaf, leaving "shot holes" in the leaf.