treating for cytospora canker
I have a large old cottonwood (poplar) with cytospora canker. In researching how to care for this disease, I don't find any mention of a chemical treatment for trees.
Is there a product that can be used to help the tree other than trimming?
The most important treatment for trees in stress is to get them out of stress. When they have a disease, it is because of environmental stresses that allowed them to become susceptible to the disease.
So the best and most important thing you can do for the tree is to water it well, including winter watering. Watering deeply and infrequently throughout the year will allow the tree to sustain it's moisture needs through the stress and heat of summer and the desiccating winds in winter.
You will need to figure out how long it takes to get water to penetrate at least 10 to 12 inches into your soil by watering and then digging a hole or using a screwdriver or other long implement to check for moisture penetration at that depth. Once you know how long it takes to get water that deep in your soil, water for that length of time each time you water. In summer that will be more frequently that in winter or spring and fall.
There is no chemical control measures available for Cytospora at this time. If the tree has portions that have succumbed to the disease you will want to have them pruned out to prevent further spread of the disease.
Here is a publication with the 12 most important diseases affecting plants in Wyoming: Landscape Pests: Integrated Pest Management Strategies for Controlling the Dastardly Dozen; Cytospora canker is addressed on page 4.