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Ash Rust is Here!

Symptoms of ash rust on the lower surface of leaves. Note orange sporulation of the fungus.
Symptoms of ash rust on the lower surface of leaves. Note orange sporulation of the fungus.

We see ash rust almost every year, but this year there seems to be quite a bit of it. The fungal rust disease is very dependent on the spores produced by the alternate host (Spartina marsh grass). In cool, humid seasons with a bit of wind, infections are numerous on ash leaves as they expand. There is no control at this time. Rake up and remove leaves that fall, as they will produce spores that go back to the marsh grass. The ash trees can tolerate some infection year after year, but it does look unsightly. There is usually no need for chemical control, but fungicides would need to be applied preventatively, so mark your calendar for next year during the second week of May, to check your trees. At that time, a fungicide such as myclobutanil could be applied to specimen trees, according to the label.

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