Month: June 2017

Tamarack defoliation by larch casebearer

Posted on by colleenrobinson
A patch of brown tamarack trees defoliated by larch casebearer caterpillars photographed during aerial survey in early June.

Larch casebearer defoliation visible from an aerial survey on June 7, 2017. Photo by Josh Haberstroh.

Tamarack defoliation by larch casebearer is evident in northcentral and northeastern Wisconsin again in 2017. The most severe defoliation occurred in Lincoln and Langlade counties, while more moderate defoliation was noted in Waupaca, Shawano and Oneida counties. I saw extensive damage in northern Wisconsin by this insect in 2014 but damage was much more localized and less severe in 2015 and no damage was documented in 2016.

Larch casebearer, Coleophora laricella, overwinters as young caterpillars and is able to start feeding as soon as the weather warms up in the spring. The caterpillars mine out the needles of tamarack causing them to turn brown by late spring. Tamarack trees will typically produce new needles after moderate or severe damage. Caterpillars pupate on the tree in early summer and moths mate and lay eggs in summer. A second round of feeding, which causes additional stress to the trees, occurs by young larvae in summer before they overwinter. Repeated defoliation can weaken the tree, making it more susceptible to mortality from eastern larch beetle.

Written by: Mike Hillstrom, forest health specialist, Fitchburg, (Michael.Hillstrom@wisconsin.gov), 608-513-7690

Periodical cicadas emerging early

Posted on by colleenrobinson
An annual or “Dog Day” cicada.

An annual or “Dog Day” cicada.

A recent article from Science Alert reported that some of the 17-year periodical cicadas associated with Brood X, have begun emerging – 4 years early! Brood X doesn’t typically emerge in Wisconsin, although it does emerge in some areas of Michigan and Illinois. The brood that emerges in a few areas of Wisconsin is Brood XIII which isn’t due to emerge again until 2024. We also have annual or “Dog Day” cicadas that emerge every summer in Wisconsin.

Cicadas are harmless, they do not bite or sting or attack people, they are not poisonous and don’t transmit disease, but they are big and the periodical cicadas emerge in huge numbers which can be quite upsetting to some people.

The problem for trees comes when the females lay their eggs. They use a stout ovipositor to puncture the twigs of small trees and shrubs, laying an egg in the slit created by the ovipositor. This damage to the tree can cause twigs to die and break off. Some young trees can be badly damaged and may lose most of their twigs and branches, they may die or be severely stunted.

An additional aggravation for many people is the very loud buzzing noise made by the males; some people refer to these insects as heat-bugs because their loud buzzing is often heard during the hottest days of the summer. 

Cicadas emerge from the ground, climb an object, emerge from their exoskeleton, and leave the empty exoskeleton behind after they expand their wings and fly off.

Cicadas emerge from the ground, climb an object, emerge from their exoskeleton, and leave the empty exoskeleton behind after they expand their wings and fly off.

For more info on periodical cicadas check out the Cicada Mania webpage.

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

Yellowheaded spruce sawfly

Posted on by colleenrobinson
There are 2 young yellowheaded spruce sawfly in this photo. As they get older they develop an orangish head capsule.

There are 2 young yellowheaded spruce sawfly in this photo. As they get older they develop an orangish head capsule.

Has anyone started to see defoliation from Yellowheaded Spruce Sawfly? This small sawfly seems to defoliate spruce without anyone noticing until it’s all done. We saw significant defoliation in 2015 (Door, Marinette, and Vilas counties) and 2016 (Outagamie, Shawano, and Waupaca counties) and if the population is going to remain high this year you should start seeing the defoliation soon. There is one generation per year and they typically feed on new expanding foliage from late May to early July. They will feed on all spruce (white, blue, Norway). The larvae blend in well with the needles so you’ll have to look closely as they can be difficult to spot.

If you have had defoliation in previous years from Yellowheaded Spruce sawfly you should monitor your spruce to determine if spraying will be necessary this year. Repeated severe defoliation can cause tree mortality.  More info can be found in this Forest Service publication.

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

White pine blister rust infections

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Spore-producing structure formed on edge of white pine blister rust canker in spring.

White pine blister rust fruit body.

White pine blister rust (Cronartium ribicola; WPBR), a naturalized pine rust disease, has been infecting white pine saplings in several northwest Wisconsin counties this spring. Although WPBR is common in the Lake States and can in some cases cause significant losses in white pine, taking several steps can help prevent infections before they start and manage them before damage occurs.

Like many foliar diseases, WPBR infections are promoted by moist and cool spring weather that results in persistent wetness on foliage; specifically, at least 2 days of wetness while air temperatures are under 68oF. Maintaining dense stocking (6×6) reduces incidence of infection by increasing the mortality of lower branches, most susceptible to infection. Similarly, successive pruning of lower branches beginning at age 5 to a minimum branch height of 9 ft. prevents leaf contact with moist surface vegetation and can increase airflow, hastening foliar drying. If caught early enough, infections can be stopped before reaching the main stem by pruning out flagging twigs and branches to at least 4 inches past the interior-most wilting needles; if the main stem is closer than 4 inches from the interior-most canker or wilted foliage, unmanageable stem infection may already have occurred and the tree cannot be saved. 

White pine sapling with significant blister rust infection causing resinous, sunken canker, and main stem girdling.

White pine sapling infected with blister rust. Photo by Kyle Young.

Written by Paul Cigan, forest health specialist, Hayward (Paul.Cigan@Wisconsin.gov), 715-416-4920.

Rhizosphaera needlecast on balsam fir

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Rhizosphaera needlecast of fir produces rows of round black fruiting bodies on the needles. Photo by Colton Meinecke.

Rhizosphaera needlecast of fir produces rows of round black fruiting bodies on the needles. Photo by Colton Meinecke.

Rhizosphaera needlecast was found on balsam fir in Shawano County, with additional reports from Todd Lanigan (West Central WI) and Paul Cigan (Northwest WI). It causes chlorosis in the needles which drop off prematurely, giving the tree a thin appearance. This disease is related to the Rhizosphaera needlecast of spruce which you may be more familiar with. Literature indicates that it is most common on fir trees in shaded damp areas, or on trees that are under stress from other issues. You will see small black fruiting bodies on the undersides of the needles, although what really stands out is the thin foliage or off-color needles compared to other unaffected trees. 

Needles from the previous year have turned brown and will drop off prematurely due to Rhizosphaera needlecast.

Needles from the previous year have turned brown and will drop off prematurely due to Rhizosphaera needlecast.

Additional info can be found in this pest alert from the Forest Service.  

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

Spiny oak sawfly

Posted on by colleenrobinson
Spiny oak sawfly creates two types of defoliation. Young larvae chew holes in the leaves, and older larvae feed on leaf material between the veins. There are 3 sawflies near the center of this photo.

Spiny oak sawfly creates two types of defoliation. Young larvae chew holes in the leaves, and older larvae feed on leaf material between the veins. There are 3 sawflies near the center of this photo.

Spiny oak sawflies are one of the many things that will feed on oak leaves. Sawflies look like caterpillars but they aren’t, so the caterpillar-specific pesticide, Bt, will not be effective on them.  Spiny oak sawflies feed between the veins of the leaves, leaving a lacy appearance to the leaves.  They have forked spines all along their bodies which turn black as they get older. I’m not aware of this ever being much of a real problem but at one site in Price County the damage to understory oaks was significant.

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

Sapsucker damage

Posted on by colleenrobinson
Supsuckers drill orderly holes through the bark into the cambium layer of the trees, causing them to bleed sap.

Sapsuckers drill orderly holes through the bark into the cambium layer of the trees, causing them to bleed sap.

Sapsuckers are birds that drill orderly holes through the bark of trees. The holes go just through the bark to the cambium layer, causing the tree to bleed. The sapsuckers then return to them later that day or the next day to feed on the sap. Sapsuckers are migratory and may just pass through an area in the spring, but they will sometimes return to the same tree over multiple years, creating new rows of holes each year. Trees will attempt to grow over this damage, and in most cases are successful. Occasionally the damage is so extensive that mortality can occur from that point up. Federal regulations don’t allow you to shoot sapsuckers, so control is usually some manner of deterrent, like wrapping the main stem with hardware cloth or burlap, or hanging scare tactics in the tree.

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

Maple petiole borer causing leaf drop in northwest Wisconsin

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Sugar maple leaf with black, shriveled petiole near leaf base, characteristic of maple petiole borer damage.

Maple petiole borer damage close up. Photo by Kyle Young.

Maple petiole borer has been active in the northwest. This exotic insect’s larvae cause tunneling damage to leaf petioles, leading to spring leaf drop in sugar maple. 

Landowners have reported leaves falling from their sugar maple for no apparent reason. While a first glance of the problem might look similar to maple anthracnose, which is a foliar disease that can also cause premature leaf drop in spring, and has also been notably active this year (see this month’s article on maple anthracnose), a closer inspection of characteristics on fallen leaves points to maple petiole borer instead. Continue reading “Maple petiole borer causing leaf drop in northwest Wisconsin” →

Oak leaftier, oak leafroller, and eastern oak looper.

Posted on by colleenrobinson
Oak leaftier rolls the leaf and secures it around itself with silk. Photo by Paul Veirauch.

Oak leaftier rolls the leaf and secures it around itself with silk. Photo by Paul Veirauch.

Localized oak defoliation near Pembine was the work of a combination of caterpillars. Oak leaftier, oak leafroller, and eastern oak looper were all found to be defoliating oak. Oak leaftier and oak leafroller can cause similar symptoms since both caterpillars purposefully roll the leaf around themselves. This trait makes it difficult to spray for them since the chemicals can’t directly reach them. When defoliation is moderate, no control is necessary. 

Oak leaftier and eastern oak looper on a ruler showing their size. Photo by Paul Veirauch.

Oak leaftier and eastern oak looper on a ruler showing their size. Photo by Paul Veirauch.

Additional information on these insects is available at these links:

http://www.forestpests.org/acrobat/oakleaf.pdf

http://www.sicktree.com/idotis/insects/lndloop.html

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

Giant hogweed (Heracleum mantegazzianum)

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Giant hogweed. Photo by Donna Ellis.

Giant hogweed. Photo by Donna Ellis.

Giant hogweed can be a threat to human health. Its sap has Furocoumarins (photosensitizing compounds) that can cause a skin reaction known as phyto-photodermatitis. This makes the skin highly sensitive to ultraviolet light. Swelling and blistering of the skin may lead to permanent scarring, and contact with the eyes can cause temporary and sometimes permanent blindness.

In Wisconsin, giant hogweed is classified as a prohibited species under the Invasive Species Rule (Wis. Adm. Code ch. NR 40). Its presence potentially causes economic or environmental harm or harm to human health. Isolated populations of Giant hogweed have been found in Wisconsin with immediate control taking place after verification.  Continue reading “Giant hogweed (Heracleum mantegazzianum)” →