The webs and damage you describe are typical of the fall webworm. In most cases the damage from the webworms is primarily cosmetic and the pecan trees survive the damage without any control measures being taken. Repeated, complete defoliations of a tree can have a greater weakening effect.

If your goal is to maximize nut production you may want to spray the tree with a product containing Bt (Bacillus thuringiensis) to control the webworms. This would need to be applied several times during the growing season. (In commercial pecan groves a recommended schedule for Bt applications to control fall webworm would be April 15, May 1, May 21, June 15, July 7, July 30 and August 15.) However, most homeowners do not own spray equipment that would reach to the top of a tree. You could hire a company to do the spraying but you would have to consider whether the value of the pecans would exceed the cost of multiple sprayings. Also squirrels love pecans and squirrels are very common in our area. Squirrels often get most of the crop of nuts produced by dooryard trees.

For additional information on pest problems of pecans see this fact sheet:

http://edis.ifas.ufl.edu/ig077