I would like to spray roundup in my common bermuda to get rid of some fescue. In reading the roundup instructions it recommends to apply in warm 60 degrees or better. Will I get good results in spraying aroung 40-45 degrees?

It won't be quite as effective at 40-45, but if the fescue is green, it should still kill it. It may take longer and may take repeated application, though.

Thanks bpgreen,
The fescue is green. I kinda thought that would be the case. Since it is mid January, I think I have enough time to do multiple apps. if necessary.

I did this a couple of weeks ago on my dormant zoysia. Chickweed and various other weeds I started withering noticably about 3 hours after spraying. They are all dead now, though I seem to have more sprouting up. The fescue (I think it was fescue, but know it wasn't zoysia as it was green) is yellowing, but there is still some green near the base. I was curious and already had RU mixed in sprayer, so I thought I'd give it a shot. I'll probably do it again in early spring before the zoysia breaks dormancy. We've been in the upper 30s and low 40s the past few days here, so I can't imagine there is too much growing going on.

RoundUp will work but just not as fast as it would if it was warmer. I have done the same in the past and have noticed that when I spot sprayed with the RoundUp RTU, the Bermudagrass surrounding the fescue will be affected and cause polka dots on your lawn when it greens up in the spring. I have also used the RoundUp concentrate and sprayed the whole lawn but I made sure that I diluted the mixture just a bit lower than the recommended lowest concentration rate. I did notice that after doing this that my lawn was delayed in the spring green up compared to other Bermudagrass lawns that were not treated.