By Laura Pottorff, Colorado
State University Cooperative Extension agent, horticulture and plant pathology
Aspen Leaf Spots
As aspen trees begin to leaf out, few of
us think about disease problems. But, if your tree has had Marsonnina leaf spot or rust
disease in the past, bud break may be the time to use preventative sprays.
Here, however, are some considerations before reaching for the fungicide bottle:
Be sure last year's black or
orange spots actually were caused by disease. Aspen leaves turn black or yellow or drop
off for many reasons -- most of them from poor growing conditions. If Marssonina or rust
is present, symptoms will appear in early August to late September. Rust will cause small
yellow or orange spots, while Marsonnina will cause round black spots. If these symptoms
occur year after year, fungicide application might be warranted. If symptoms don't occur
every year, fungicides usually are not necessary.
Think about what other types of
control strategies you could use in place of or in conjunction with fungicides. Fungicides
are widely overused in urban areas and even when their use is justified, they may need a
little help. You can minimize Marssonina and rust diseases by cleaning up infected leaves
that drop to the ground in the autumn. The fungus overwinters on this leaf debris and if
we clean up as much debris as possible, less "inoculum" will be present to begin
the disease cycle over again in the spring.
Photo: Judy Sedbrook
Back to Diseases
Back to Home