I couldn't really find anything regarding temp either, except for a study on crabgrass and effectiveness and different temps...
https://www.ncbi.nlm.nih.gov/pubmed/19235182
It found effectiveness at all temps, but my guess is that you're more worried about ill-effects on your babies at higher temps.
https://www.ncbi.nlm.nih.gov/pubmed/19235182
It found effectiveness at all temps, but my guess is that you're more worried about ill-effects on your babies at higher temps.