Hello and thanks for reaching out to Ask Extension!

The first photo is some type of fir tree with some pretty extensive webbing that is most likely spider mites which are especially active in September.  For control you can physically knock down the webs with a strong stream of water and then apply insecticidal soap or horticultural oils like neem oil. 

I am thinking by Arbs you mean Arborvitae? For Arborvitae:

Because arborvitae depend heavily on water, consistent deep watering is essential, especially when they are newly planted and during extended dry periods. Applying a layer of mulch can help retain soil moisture.

Water thoroughly through September, and continue watering until the ground freezes in your area. During winter, water during thaw periods when possible. Loose soil and mulch help water penetrate more effectively to the root zone.

If arborvitae needles brown and drop prematurely during hot summers—even with adequate watering—resulting in thin areas, spider mites may be the cause, especially when damage appears on the south or west side of the tree.

You also might notice that the older and inner needles of the tree begin to yellow and fall to the ground. This is part of the natural life cycle of arborvitae and is nothing to be alarmed about.

Powdery mildew is not an issue that impacts either of these plants.

None of the extension resources recommend hydrogen peroxide treatment for plants for any reason.