Walnut tree staining over new deck

[dakotalawdog]

I just put on a new deck with composite boards. Two weeks in and I’m getting staining in some areas from two walnut trees about 15 feet off the deck. Several branches overhang the deck.

What causes this? I know the nuts stain but there are no nuts actually dropping on the deck.

My big question is - Would I likely be alright just pruning the branches that over hang the deck or is having the trees this close just going to cause continual issues with the staining?

Parts of the deck not directly underneath seem to not be staining so I’m inclined to try pruning first but wanted to ask someone who might more than me.

 

[ATH]

Is there something eating the leaves? Or perhaps scale on the walnut???

How big are the overhanging branches? If they are a relatively small portion of the tree, then sure, have them pruned back.

 

[buzz sawyer]

Pics are always helpful - and easy to post.

 

[dakotalawdog]

I pressure washed it clean last night. This morning the areas of the deck are covered in little black specs. It’s not squirrels leaving shrapnel, my guess is it’s something off the leaves or the bark?

Someone here has to know walnut trees a bit.

Here are the pics. My plan for now is to prune see if that helps, otherwise it’ll have to come down.
And I was mistaken, it’s just one walnut. The one next to it is an elm I believe.

 

[JTM]

Caterpillar poop.

 

[Del_]

Caterpillar poop.

That's right I bet.

 

[djg james]

Not just mildew from morning dew and being in the shade longer than the rest of the deck?
Don't know if Walnut drops sap like other trees do. I'll have to look it up.