Your landlord is probably within his rights to insist on an opportunity to properly maintain his property -- even when that means exposing his tenants to possibly harmful chemicals. It is unlikely that a judge would deprive an owner of the ability to perform a customary maintenance procedure, though a judge might insist that the landlord try to address the problem with a less toxic chemical if one exists.

If you feel that you can't continue to live there after the tenting, you ought to look for alternate housing.

As a compromise, you might suggest that you and the landlord strive to work out an arrangement for other housing until the threat of the chemicals has waned.