I am unable to image a picture of the brown fuzzy things. Could you reply to the message with a picture of the brown fuzzy things that are all over your ash trees? I am sending you links to a few possibilities.
 Do they look like spider webs? Here are sites with information about spider mites.
https://hortnews.extension.iastate.edu/2008/10-8/ashspidermite.html
http://www.extension.umn.edu/garden/insects/find/spider-mites/
These sites have information on another type of mite called eriophyid mite. They cause staminate flower galls.
http://igrow.org/gardens/gardening/ash-tree-issues/
http://www.extension.iastate.edu/news/news/2006/jul/072801.htm
http://www.extension.umn.edu/garden/insects/find/insect-and-mite-galls/
The last site may help you to diagnose other problems with your ash tree.
http://www.extension.umn.edu/garden/diagnose/plant/deciduous/ash/

Here are a couple pictures of my "brown fuzzy things". The chemicals I apply to the trees each year are Bifenthrin and Dinotefuran. Back when I paid to have it done they used Imidacloprid but I chose not to use that.

Here are a couple pictures of my "brown fuzzy things". The chemicals I apply to the trees each year are Bifenthrin and Dinotefuran. Back when I paid to have it done they used Imidacloprid but I chose not to use that.

The brown fuzzy things are called staminate flower galls. They are caused by a eriophyid mite. The mite causes male flowers to grow into round greenish, 1∕2 to 1 inch diameter tumor-like structure in spring. They turn brown and woody in late summer.  The do not harm the health of the tree.  They overwinter on the buds of the tree. It is difficult to control the mites because they must be killed before galls begin to grow in the spring. Look for the first signs of green in the opening flower buds. An application of carbaryl (Sevin) in the spring when the first blossoms begin to form will reduce the number of galls.
http://igrow.org/gardens/gardening/ash-tree-issues/
http://www.extension.iastate.edu/news/news/2006/jul/072801.htm
http://www.extension.umn.edu/garden/insects/find/insect-and-mite-galls/
http://hort.uwex.edu/articles/ash-flower-gall/

Thank you - a couple questions please:

1. How do you apply Sevin?  These trees are too large for a hand sprayer.
2. What is your opinion of the other two chemicals I apply each year?

We do not recommend chemical treatment for ash flower galls.  The flower galls do not affect the health of the ash tree.  It is difficult to precisely time the chemical treatments so it may not work.  You will need to hire an arborist to spray the miticide who has the expertise and equipment to reach the flower buds at the top of the tree.  

This site has another picture of ash flower galls.

http://www.extension.umn.edu/garden/diagnose/plant/deciduous/ash/flowersgall.html

 

Systemic insecticides are generally considered to have less impact on natural enemies than broad-spectrum insecticides applied as foliar or cover sprays

 

Bifenthrin is a spray applied as a preventive trunk, branch, and foliage cover. Two applications at 4-week intervals are required.  The first spray should occur at 450-550 degree days (50ºF, Jan.1); coincides with black locust blooming.   

Dinotefuran is an insecticide in the neonicotonoid class.   The Neonicotinyl active ingredients are found in imidacloprid, dinotefuran, thiamethoxam, and clothianidin,  acetamiprid and thiacloprid . The use of neonicotinyl insecticides as trunk injections and soil drenches for ash trees is important to slow the spread of the exotic, invasive Emerald Ash Borer.  Bees do not collect ash pollen in quantities so the risk to bee pollinators is low.

 

http://www.extension.umn.edu/garden/plant-nursery-health/protecting-bees-beneficial-insects-systemic-insecticides/

http://www.extension.umn.edu/garden/insects/find/emerald-ash-borer/docs/potential-side-effects-of-systemic-insecticides-used-to-control-eab.pdf