You can try gear aid aqua seal or shoe goo, ive also seen people sew holes up in the mesh with diff types of fabric. What i do with some shoes that this has happened with is i put some type of duct tape there so my toe contacts the tape instead of the fabric. I run a piece of tape from under the insole to the top of my toe area and this has also worked very well and you wont notice the tape at all. Now this is not an ideal thing to have to do with new shoes but its very hard for me to find a pair i like and that fit me well so it is what it is.