What we're seeing now

June 21, 2013

Bark beetles in red pines

Earlier this month, DNR Forest Health staff was alerted to a row of red pines showing shoot dieback and mortality near Mora in Kanabec County. These trees were up to 30 feet tall and trees with symptoms were clustered. Over the next two weeks, bark beetles were found in the stems near branches with red needle symptoms. Bark beetles were still laying eggs during the week of June 10. Symptomatic trees should be removed and destroyed, burned, or debarked within three weeks to prevent bark beetles from spreading to adjacent pine trees.

Early symptoms of Bark beetles on red pine

Early symptoms of Bark beetles on red pine

Red pine two weeks later

Red pine two weeks later

 

Winter-burn on red pine

Some winter-burn symptoms are visible on roadside red pines statewide. Reddish-brown needles are the result of desiccation during the winter, which can be related to soil conditions as well as road salt splashed onto the needles. In some cases it is just one or two trees with symptoms in a row of otherwise healthy-looking trees. Like the other red pines, symptomatic trees are just beginning to form candles. Typically, winter-burned trees will recover and the new, green growth will hide the brown needles.

Winter burn on red pine close up

New growth on red pine shoot with winter burn

Winter burn on red pine

Winter-burn on red pine

 

Cytospora canker of spruce

Death of isolated or random branches on white spruce seen in the Central region can indicate infection by Cytospora canker. Top-kill might also be involved. Look near branch nodes for small, pitchy cankers below the bark and the presence of small, black fruiting bodies. Often, pitchy exudates are produced at the base of infected branches. This is a contagious disease, so sanitize your pruning shears or saw before moving to another branch or tree. Burn or destroy clipped branches and dead trees.

Cytospora canker of spruce

Cytospora canker of spruce symptoms

Cytospora canker of spruce

Cytospora canker of spruce symptoms

Cytospora canker of spruce

Cytospora canker of spruce symptoms

 

Forest tent caterpillars

Forest tent caterpillars (FTC) are 1.5 to 2.0 inches long from Grand Rapids to Backus to Mahnomen County as well as counties in Central Minnesota. Forest health specialists are starting to see some defoliation but not much yet and just in tree tops. Near Tower in St. Louis County, the caterpillars are 1.0 to 1.75 inches long and no defoliation is visible. In many areas, the basswoods seem to be showing the defoliation first. Caterpillars are crawling across roads and parking lots and up the sides of houses in small numbers. This will increase as they continue to grow in size over the next two weeks or so.

Enjoy the caterpillars while you can; in two weeks they will pupate and develop into moths. You can hear the frass (insect droppings) falling like rain under trees being defoliated. It's best to avoid any picnics with open-face peanut butter and jelly sandwiches or potato salad under these trees for a while. You could always sprinkle a lot of pepper on the potato salad and maybe no one will notice.

Noticeable populations of friendly flies, parasites of FTC pupae, can be found near Grand Rapids, Tower and near Elbow Lake in Mahnomen County.

Forest tent caterpillar

Forest tent caterpillar June 20 near Cook MN

Forest tent caterpillar resting on aspen trunck

Forest tent caterpillar resting on aspen trunk

 

Jack pine pollen cone crop

The pollen (or staminate) cones on jack pine are very heavy and some of the jack pine even look tan from the distance because of this. This is a very widespread occurrence. Cones are still releasing pollen in NE and NW Minnesota, but will fall off in the next week or so. These pollen cones serve as the preferred food source for young jack pine budworm larvae.

Jack pine pollen cone crop

Jack pine pollen cone crop

 

 

Jack pine budworm

A jack pine budworm larval survey was conducted in the NW Region, but none were detected. This is quite surprising, considering how often jack pine budworm outbreaks occur there. In the NE Region, a couple of larvae were found in central St. Louis Co. near Esquagama Lake. This year's aerial survey will tell us the whole story, but for now, it appears to be a good year for jack pine vigor and growth.

Jack pine budworm

Sampling for young budworm larvae in male cones

 

 

Spruce budworm

No defoliation from spruce budworm is visible yet. As of June 13 the spruce budworm larvae were still under the bud caps on the white spruce in northern St. Louis County. On white spruce, spruce budworm larvae web the bud-cap onto the end of the new shoot and use it as a hiding place from predators. On June 20, larvae were 7/16 to 3/4 inch long near Tower in St. Louis County.

Spruce budworm

Bud caps webbed onto white spruce shoots by spruce budworm larvae

Spruce budworm

White spruce shoots damaged by young spruce budworm larvae

Spruce budworm

Spruce budworm

 

Black Ash

Summer must be on the way, because black ash decided that most of the danger of frost is past and have started to leaf out in northern Minnesota.

Black Ash damage

Black ash leaves just emerging June 13 near Tower Minnesota

 

Elm and maple

There is heavy seed-set in some of the red and silver maples seen statewide, so heavy that some trees look tan and others pinkish or reddish due to all the seeds. Some red maples apparently developed only flower buds last fall and now have just seeds and no leaves. Others are a mix of seeds and leaves. These trees will leaf out after the seeds fall off, so some of them will be bare and look nearly dead for a short time before the foliage fills in.

Heavy seed set on Maples

Heavy seed set on red maple tree

 

Eriophyid mites on maple

The bright red, felt-like areas visible on maple leaves are caused by eriophyid mites. They are not detrimental to the tree's health or vigor but may cause some leaves to distort. This can be seen statewide.

Eriophyid mites on maple

Maple leaf with Eriophyid mites

 

Scab and black canker of willow

These two exotic diseases haven't been seen in Minnesota since the mid-1980s, when they swept into and through the state. They were introduced into New York before 1920. Native willow species are rarely affected, so it's the European species that bear the brunt of these diseases. Twenty- to 80-year-old willow trees on two sites in Cass County look like scab and black canker have been active there for at least two years. Every twig and branch is dying back and the foliage is 99 percent dead. These diseases can kill anything from seedlings to over-mature willows, so the prognosis is not good, especially with cool and rainy spring weather.

Spruce budworm

Spring symptoms

Spruce budworm

Spring symptoms

Spruce budworm

Spring symptoms

 

White pine bark beetles

There are many reports of top-killed white pine around the southern half of the state. Driving a circuit from St. Paul to Hinckley to St. Cloud and back to the metro area, staff counted hundreds of afflicted white pines. The cause is a very small bark beetle called Pityogenes hopkinsi. When examining white pines, look at the top-killed portion and you will see lots of resin dripping from tiny, pin-sized holes. Gently peel back the bark to reveal the small, chestnut-brown beetles and their galleries. These beetles prefer to attack the smooth bark of stressed pines, and it would appear the drought last year has triggered an outbreak. So far, only young pines less than 20 feet tall are being attacked.

Spruce budworm

White pine stand

Spruce budworm

Resin dripping down the trunk

Spruce budworm

White pine showing top-kill

 

Anthracnose

Anthracnose is a general term for a group of hardwood diseases that cause lesions on leaves and fruits, and is being observed statewide. Generally, these diseases are cosmetic and cause no serious damage to the tree. There are many species of fungi known to cause anthracnose, but most only infect one or a few specific host species. Therefore, these diseases are named for the tree species on which they may be found. Anthracnose is most severe in years when there is a cool wet spring at the time of leaf expansion when the initial infections occur. The disease can intensify if those conditions persist through the growing season. Bur oak anthracnose has been very common this spring, and is easily identified by black leaf lesions and curling leaves (don't confuse anthracnose with bur oak blight or oak wilt). We have also had many reports of maple and ash anthracnose. Some trees will shed their infected leaves as the growing season progresses. You can rake up these leaves and destroy them before next spring to reduce disease levels next year.

Forest tent caterpillar

Anthracnose on leaves

Forest tent caterpillar resting on aspen trunck

Anthracnose on leaves

 

Larch casebearer

Early in the growing season, larch casebearer can be found in young tamarack stands. Larvae mine single needles, then wear them like snail shells while feeding on the outside of the remaining needles. Only a skeleton of the needle remains attached to the green needle base. As the season progresses, these needles fade to orange and pale tan. Affected trees may be spotted while driving by on the highway. Although larch casebearer larvae don't kill the saplings outright, growth rate is likely reduced.

Spruce budworm

Larch casebearer on a tamarack

Spruce budworm

Symptoms of larch casebearer on tamarack branch

Spruce budworm

Tamarack trees damaged by larch casebearer