Aspen leaking sap and bulbous areas - Ask Extension
Hello. I live in Denver, and have several young (< 5yr) aspen trees. Each year, we've noticed bulbous areas on the branches (see pic), and are ...
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Aspen leaking sap and bulbous areas #121584
Asked April 14, 2013, 3:09 PM EDT
Hello. I live in Denver, and have several young (< 5yr) aspen trees. Each year, we've noticed bulbous areas on the branches (see pic), and are wondering what this is. This year (now) we noticed a red sap leaking from some of the branches / trunks (see pic). My google search showed "canker" or some sort of bird or insect could be boring. Please advise. Should we remove these aspens? It would be a shame, but I'm concerned about a disease spreading to other trees such as pear, maple, and autumn purple ash. Thanks in advance!
Andy
Andy
Arapahoe County Colorado
Expert Response
The bulbous areas on the branches are most likely the Poplar Twiggall Fly, which gives the branches a knobby, gnarled look. Control with insecticides have not proven effective because the timing of application must coincide with adult activity periods. Pupation occurs in late winter/early spring, slowly growing in the summer and rapidly growing in the fall. A lot of homeowners choose to prune out the galled branches, however, this will eventually affect the overall look of the tree.
The leaking red sap is most probably Cytospora canker (fungus). This is extremely common in landscape aspens. The fungus attacks trees that are stressed, or the Cytospora can develop around a gall, like you described on your trees. There is no chemical treatment for this fungus that has been shown to be effective.
Although Cytospora species can infect different tree species, the one that one that infects aspens will not spread to the other trees you have in your landscape. This particualr Cytospora will stay with aspen & cottonwood species.
The Denver Metro areas is really too low of an elevation to grow aspens and have them live healthy for any number of years. There are many other wonderful trees that can be grown as an alternative to aspens.
I've included some links that might be helpful for you:
http://www.ext.colostate.edu/pubs/garden/02937.pdf
http://www.ext.colostate.edu/pubs/insect/05579.pdf
http://www.colostate.edu/Depts/CoopExt/4DMG/Garden/Amazing/aspendon.htm
http://www.colostate.edu/Depts/CoopExt/4DMG/Trees/aspens2.htm
http://www.colostate.edu/Depts/CoopExt/4DMG/Trees/aspencan.htm
The leaking red sap is most probably Cytospora canker (fungus). This is extremely common in landscape aspens. The fungus attacks trees that are stressed, or the Cytospora can develop around a gall, like you described on your trees. There is no chemical treatment for this fungus that has been shown to be effective.
Although Cytospora species can infect different tree species, the one that one that infects aspens will not spread to the other trees you have in your landscape. This particualr Cytospora will stay with aspen & cottonwood species.
The Denver Metro areas is really too low of an elevation to grow aspens and have them live healthy for any number of years. There are many other wonderful trees that can be grown as an alternative to aspens.
I've included some links that might be helpful for you:
http://www.ext.colostate.edu/pubs/garden/02937.pdf
http://www.ext.colostate.edu/pubs/insect/05579.pdf
http://www.colostate.edu/Depts/CoopExt/4DMG/Garden/Amazing/aspendon.htm
http://www.colostate.edu/Depts/CoopExt/4DMG/Trees/aspens2.htm
http://www.colostate.edu/Depts/CoopExt/4DMG/Trees/aspencan.htm
