Photos of the Week


Here are some petri dishes with Armillaria glowing. In the back ground is a bag of wood sawdust inoculated with Armillaria which is also glowing.

 Petri dishes and bags of bioluminescent fungi glowing in the lab. Armillaria and Panellus are two fungi that have mycelium that glows in the dark.

pine board with white pocket rot

A pine board with white pocket rot. These interesting white rot fungi have the ability to selectively degrade lignin leaving cellulose behind. Some fungi, such as Porodaedalea (Phellinus) pini, produce small spindle-shaped white pockets while some other white pocket rot fungi produce much larger zones of delignification.

Blue stain in pine bowl

Blue stain fungi impart dark discoloration to wood from their pigmented hyphae. Blue stain can lower the quality of wood used for wood products but in some cases, such as this turned pine bowl, it can add value.

zone lines

Zone lines or pseudosclerotial plates are made up of fungal melanin that acts to separate incompatible white rot fungi from each other. Often called spalted wood, it is used by woodworkers and artists to make interesting objects.

hawthorn rust

Aecia on the bottom surface of a hawthorn leaf caused by Cedar-Hawthorn Rust, Gymnosporangium globosum.

Telia on Juniper Broom rust

Telia emerging from the branches of Juniper Broom Rust in the spring caused by Gymnosporangium nidus-avis

cone rust

Cone rust affects southern pines and the entire infected cone becomes a site for production of aeciospores. These spores infect the alternate host, evergreen oaks.


Gall rust aecia

Pine oak gall rust with aecia producing aeciospores. 


blister rust

Aecia of white pine blister rust on an infected white pine. The aecial stage is only seen in a 1-2 week period around the beginning of June. This blister-like aecia give the disease its name "blister rust".


When mature and released from the hysterothecia, the long thin ascospores have a sticky sheath that helps them adhere to needles.

Lophodermium has long, thread-like ascospores with a sticky sheath that helps adhere them to needles after they are ejected out of the hysterothecium. 


Hysterothecia (also refered to as apothecia covered by stroma) on pine needles infected by Lophodermium.

Lophodermium on old pines needles showing the black hysterothecia. These open producing ascospores from the compressed apothecium that is under the black stromatic material.


The fungus causing oak wilt produces fungal mats under the bark.

 A red oak infected with oak wilt the previous year will produce oak wilt mats under the bark. In spring, the pressure pads break open the bark and the aromatic fungus attracts Nitidulid beetles. The photo shows the pressure pads of the fungal mat when the bark was removed. These mats would be filled with conidia and if both mating types are present, perithecia will form.


Dead Before and After

 The University of Minnesota Saint Paul campus looking toward the student center from Cleveland Ave before (left) and after (right) large losses of elms from Dutch elm disease.


Eutypella cross section

Have you seen the inside of a tree with a large Eutypella canker? This cross section of a tree through the canker shows many years of reaction wood forming in the tree. Photo by Matt Kasson.


cankers on madrone

There are many different types of canker fungi and many have not been studied. Here are interesting perennial cankers on Madrone from Arizona


newman canker

 What fungus do you think caused this type of canker on this ash tree?


maple anthracnose


This home owner asks "Is my tree going to die?" Maple anthracnose can cause problems in the spring and early summer. Will his maple tree die?


Anthracnose on oak after early spring infection. Symptoms can look like a wilt disease.

Spring infection of oak with oak anthracnose can mimic the symptoms of oak wilt. However, there are ways to differentiate oak wilt from oak anthracnose. Can you determine this?


wrapped tree with twine

 Tree wrapped with heavy twine to prevent winter sunscald. This is a method used in China. Apparently it is effective but very labor intensive to put on and take off each year.

Iron chlorosis

There are many different types of abiotic or non-infectious agents causing tree problems. This pin oak is located in downtown St Paul. What is causing this tree to decline?

red pines

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.