Question
Hi, I have 4 quaking aspen that we have built a treehouse on. I think that they might have a disease. Over the past few years branches have been dieing off from the ground up. There is also a thick orange fluid dripping out of some places in the bark.
    What can I do to stop the disease, and what kind of fungicide should I use?
    
    ps. We have some pivot fungicide that we use for barley. will it work? If not, what fungicide will.

Thanks.

Answer
Cytospora canker: The fungus that causes this canker (Cytospora chrysosperma) is weakly parasitic and normally attacks stressed trees. Although C. chrysosperma is the most common canker fungus on aspen throughout the tree's range, the fungus often is associated with other, more aggressive canker fungi. Small twigs and branches can be killed without the formation of a distinct canker. Trunk cankers usually have an irregular outline, with sunken, orange-discolored perimeters (figure 8).

The first indication of infection is the orange discoloration of the bark surrounding the wound. After infection, the inner bark turns dark brown and the sapwood underneath light brown. The dead bark falls from the tree in large pieces after 2 to 3 years.

Pimple-like fruiting bodies, called pycnidia, which exude orange to red-colored spore masses in hairlike coils, are produced during wet weather several weeks after infection. During rains, these spores are partially washed away and can spread into new wounds. Insects visiting infected trees may also vector the fungus.

Perithecia are produced later in the same areas as where pycnidia developed. These structures are the sexual state of the fungus (Valsa sordida).

Because this canker usually occurs on a weakened host, the first and foremost method of control is to prevent infection by preventing stress on the tree. Drought and flooding soil with water are the two most common stresses that predispose trees to cytospora infection.

Wounds caused  are prime targets for infection on trees in landscaped areas. The tree house is a wound.

Once infection occurs, the best treatment is to increase plant vigor and sanitation. Remove all infected limbs and other areas. When removing branches, make a smooth cut at the base of the limb, as near the trunk as possible, without damaging the branch collar (swollen area at base of branch). Jagged and rough cut surfaces promote infection.

Clean wounds to avoid further spread of infection. Remove dead bark to dry out the diseased area and help the tree defend itself against insect and fungal attacks on the cankered area. Directions for proper wound and canker treatment are as follows:

Prune or cut trees only during dry weather.
Clean tools and wipe them with ethyl alcohol, Lysol or other disinfectant. Clorox may be used at a concentration of one part Clorox to nine parts water.
If a wound is fresh (one month old or less), use a sharp knife to carefully cut and remove all injured or diseased bark back to live, healthy tissue. If the wound is older, just remove loose bark pieces. It is important not to cut, remove or damage callus that may be forming at the canker edge. Callus will look like swollen bark growing across the dead area. Scrape the wound surface clean of loose bark.
Clean tools and disinfect after each cut.
Cleaned wounds should not have any sharp angles.
Do not apply any tar, oil-based paint or other wound dressing. The best method to prevent infection or decay is to allow the cleaned tissue to dry out.
Fungicides will not help.