Yes, they can. The lanldord has an obligation to *all* its tenants to maintain a pest-free environment. That can only be done by spraying or exterminating in all units, since any unit not exertminated can provide a locus for an infestation to develop. That you are allergic to these chemicals does not override the landlord's obligation to the entire apartment community. You also cannot force them to spend more for a "natural" product or use a less-effective natural product, since it is not reasonable for them to change their behavior in regards to the whole building for one tenant.