Brown Leaf spots everywhere

Hello all, not sure if this is the right place
but, never before until this year alone
brown or black spots on leaves are found everywhere around my neighbourhood.

I don't mean just on tree, but pretty much every tree within a 60mile radius.... that I know of, maybe more beyond that but haven't ventured.

at first i didn't make anything of it, but now it's on every single tree everywhere.

i'm in Montreal, Canada.

is this affecting anyone else, never had this any other year, only this year.

is it harmful to humans?

Rhytisma

Not harmful to humans unless you are particularly mold sensitive; although I wouldn't eat the leaves. Marginally harmful to the trees; just ugly. To reduce chance of recurrance next year, rake and compost leaves or conduct a controlled burn after the leaves are all down. It helps if the whole neighborhood gets involved.

nu-distance.unl.edu...
plantclinic.cornell.edu...

Sri Oracle



[edit on 22-9-2007 by Sri Oracle]

To me that looks like what is commonly called "Rust," a fungal infection of plants. It is quite common and if it is increasing, it could be a sign that other factors are making the plants weak or stressed. Stressed plants are less able to deal with such problems. It could also indicate that the Rust has gotten stronger and that the plants will have to find a new way to fight back. Plants constantly evolve new defences against insects and other problems and perhaps this is just another cycle.

Rust is usually red, though. This is very unusual. It resembles black spot, but that is a disease of roses and strawberries.

it's definitely fungal. Ah, I see Sri Oracle nailed it.

Rhytisma. Also called tar spot. Apparently it's not deadly to the trees, but heavy infestations can cause early leaf drop.

There are other leaf spot diseases, though.

According to a poster on this forum, it's been happening in the Toronto area for 10 years or more.

You're lucky, it won't hurt your trees. We're dealing with sudden oak death.

Perhaps it's a sign of global warming, fungi moving into ranges they weren't in before.

You may be able to boost the immunity of individual trees by mulching with scraps of ACQ treated lumber. No source... just a gut on that one.

Sri Oracle