I have written about this problem a few times on this site and it might be worth a visit to one of my previous posts if you are interested in learning about CTV:
Identifiying Tomato Curley Top Virus
In addition there is more info on this problem through New Mexico State University (NMSU) here.
The reason I put row cover over my plants is to have a physical protection to keep the Beet Leafhopper off of them. I remove the row covers when the monsoons come in July as they seem to either leave or become suppressed and then I usually don’t have any problems with leafhoppers and CTV. No insecticides seem to work. If it seems that I harp on this problem, I do! I just want you all to be successful with tomato growing here.