California Civil Code section 1940.8.5(b)(1) provides as follows:
"A landlord or authorized agent that applies any pesticide to a dwelling unit without a licensed pest control operator shall provide a tenant of that dwelling unit and, if making broadcast applications, or using total release foggers or aerosol sprays, any tenant in an adjacent dwelling unit that could reasonably be impacted by the pesticide use with written notice that contains" various information, including the pest or pests to be controlled, the name and brand of the pesticide product proposed to be used, and the approximate date, time, and frequency with which the pesticide will be applied.
There's a lot more to it, and I'll leave it to you to read it and ask questions if needed.
The rub, of course, is that weed killers are not necessarily pesticides. "Pesticide" is defined in sub-section (a)(7) to mean "any substance, or mixture of substances, that is intended to be used for controlling, destroying, repelling, or mitigating any pest
or organism, excluding antimicrobial pesticides as defined by the Federal Insecticide, Fungicide, and Rodenticide Act."
Weeds are, of course, "organisms." However, "pest" is defined in sub-section (a)(6) to mean "a living organism that causes damage to property or economic loss, or transmits or produces diseases." I think you'd be hard-pressed to characterize weeds as "pests" using this definition.
I could find no other applicable law in
the portion of the Civil Code governing residential real property.
tl;dr: It doesn't appear that the pesticide notification laws apply to weed killers, and there appear to be no other laws specifically governing the use of weed killer.