Question
We planted sod about three weeks ago and because of all the steady watering, the weeds in the existing soil are popping up in abundance!  We don't want them to take over the lawn, but is now a good time to apply a lawn weed killer, perhaps without fertilizer, since we are in our hottest months of the summer here in New Mexico??  If so, what would you recommend for newly established sod?

Answer
You can put down a weed killer (without fertilizer) but there is a certain amount of work which you need to do beforehand. You have to ensure that you can apply it accurately. It must be a post emergent weedkiller which will not harm the turf. Check the label to ensure that temperature conditions are right. In any case, it is better to apply weedkillers early in the day. Watering will continue to be a critical issue because you want to put on enough to keep the grass growing but not so much as to nullify the effect of the weedkiller.
It is a good practice to load up the soil with enough moisture to take things through the next 14 days.