Photos of the Week

Very large mushroom

After taking this class, a walk in the forest will never be the same. I hope you find some interesting fungi out there!

Dwarf misletoe on black spruce

Dwarf mistletoe, Arceuthobium pusillum, causing large witches' brooms on black spruce in northern Minnesota

Galls on cottonwood

Large galls on cottonwood in Minneapolis. 

Davy with rhizomorphs

Rhizomorphs of Armillaria. These subcortical rhizomorphs were pulled off from under the bark of a downed tree that had root rot.


Armillaria fruiting at the base of a tree with root rot. In Minnesota, Armillaria fruits for a short time usually in mid to late September.

Maple bowl with ambrosia beetles and stain

Ambrosia beetles tunnel into the xylem of trees bringing specific species of blue stain fungi with them. The larvae of the ambrosia beetles feed on the fungus. Streaks of discoloration associated with the beetle galleries can be seen in this turned maple bowl resulting in a strikingly beautiful piece of art. 

White pocket rot in wood

A split open conifer log showing a white pocket type of wood decay. Fungi causing this decay have the ability to remove large amounts of lignin but leave cellulose. The white pockets are areas of delignified wood. These fungi are of great interest for their potential in bioprocessing applications where lignin removal is needed such as biofuel production, biopulping, biobleaching of pulps, etc.

Zone lines lamp

A lamp made from spalted maple with zone lines (pseudosclerotial plates) produced by white rot fungi.

Juniper broom rust

Juniper broom rust. Telia are produced out of the branches on the broom in the spring during wet weather. The alternate host for this rust is serviceberry.

Blister Rust

Aecia on white pine produced by white pine blister rust. The aecia (blister like structures) are filled with aeciospores that are released and infect Ribes. 

Brown spot on longleaf pine

Needles of longleaf pine from Alabama infected with brown spot. Each lesion (yellow/brown spot) on these needles is a separate infection.

oak wilt mat with Nitidulid beetles

A fungal mat formed under the bark of a red oak with two Nitidulid beetles feeding on it. Pressure pads produced by the mycelial mat breaks the bark open and the aroma produced by the fungus attracts the beetles. The beetles can carry fungal spores that were produced on the mat to healthy trees when they feed on the sap flowing from fresh wounds.

DED Campus BeforeDED Campus After

On left: the University of Minnesota St Paul Campus in 1970's before Dutch elm disease started to take its toll. Big elms lines all the campus streets. This picture shows where the buses stop outside of the student center. On right the same location a few years later. Most of the elms had been removed due to Dutch elm disease but a few remain due to good sanitation methods of control and tree injections with fungicide.

Chestnut carving

Finding items made from American Chestnut are rare. This carving shows the fine characteristics of chestnut - a favorite wood to use in the 1800's (and before) for building homes and just about everything in it. The blight, arriving about 1904, changed all that. 

Black knots on cherry tree

Ornamental Canadian Red Cherry heavily infected with black knot. A row of these trees in Roseville all are severely infected. How should this have been controlled years ago?

Canker on ash tree

What fungus caused this canker on ash?

Rhytisma acerinum on maple

This homeowner asks for help: "Big black spots are everywhere on the tree and leaves are falling off". The introduced tar spot, Rhytisma acerinum from Europe, is causing lots of problems in the US. It appeared in Minnesota a few years ago and is becoming prevalent on Norway maples. 

Maple anthracnose

Is my tree Dying? This homeowner was very upset to see his maple looking so bad and thought it was going to die. This is maple anthracnose and in wet, cool spring environments it can cause a lot of infection and defoliation. Although trees look bad and can be stressed due to the defoliation, most trees recover.

Bread mold

Mold growing on old bread. The blue / grey coloration is from the production of pigmented condidia by the fungus. See below photo for a high magnification of the conidia.

Penicillium spores

Some of the bread mold mounted to show the conidia on conidiophores. Long chains of spores are produced on the moldy bread. This fungus is Penicillium.

Wrapping trees to prevent winter injury

To prevent winter injury caused by winter desiccation and also to prevent salt damage this homeowner wrapped their conifers. They also decided to decorate the wrapped trees for the holidays.

wrapped tree

To prevent winter sunscald in northern China, they had wrap trees with twine completely covering the trunck and main branches. This acts as a buffer to stop fluctuations in bark temperatures. It is a tremendous amount of work but it apparently works well.

red pine trees

Keeping forest and urban landscape trees healthy requires a good knowledge of tree diseases. This class will provide you with important information you can use in the future. Watch this page for new photos each week.