'Leaf spot' fungus on aspen/cottonwood trees
Notice the brown spots on cottonwood and aspen trees in town this year?

It’s a fungus called Marssonina, which causes dark brown flecks, often with yellow halos.

“Marssonina will not kill the tree unless the fungus occurs several years in a row and the tree defoliates early each year as a result of the fungus,” said City Forester Chris Forman, who attributes the appearance of the fungus this year in Aspen due to heavier moisture levels than usual.  

There is no spray or treatment that will be effective this year, Forman warned.

“The only management that can be done for the leaf spot fungus at this point is to rake up the leaf litter this fall,” he said. 

Since Marssonina survives the winter on fallen leaves that were infected the previous year, it is important to remove the infected leaves, twigs and branches this fall.

Also, keeping leaves as dry as possible can reduce the incidence of leaf spots. Residents are encourages to:
•    Water in the early morning so leaves can dry out;
•    Keep sprinkler patterns adjusted so leaves don’t stay wet;
•    Space trees apart to reduce humidity to help prevent leaf diseases.

Have questions? Contact City Forester Chris Forman at 970-429-2026. 

Posted on Friday, August 13, 2010