What temperatures are required to sucessfully use herbicides to kill grass and broadleaf weeds?

I am in Tennessee and I had a guy from a company called Chemlawn today tell me that they were spraying for broadleaf weeds as well as applying pre-emergent and fertilizer to their customer's lawns.





I was surprised especially considering that it is not even yet middle February and they are already using post emergent herbicides on the lawn.





Is it really possible to do this when the temperatures are still getting close to freezing at night?








Thanks for your answers!

What temperatures are required to sucessfully use herbicides to kill grass and broadleaf weeds?
The pre-emergent is for crabgrass. What they do is two half rate applications, so it has a longer residual effect. At the same time they are putting out post emergent for broadleaf weeds, because henbit and other weeds will be popping up after all the rain you have had. They will put out the next application in about 6 or 7 weeks.





The fertilizer is potassium for root development. During the cooler part of the season that is what you work on. Develop a healthy root system and the top growth will show it.





Chemlawn is a major company (Fortune 500) and would not be doing something to lawns they shouldn't be doing. Can you imagine they would put out these products on a few thousand lawns, just to have to replace the lawns?





I am from the Birmingham area. They know what they are doing. :)





One of the first things you will think is they have 'killed your grass' because weeds will be dying and you will think it is grass. then as spring rolls around your real grass will become thicker and greener and you will see the difference. One little know fact is that weeds grow faster than grass.





Hope this helps. :)
Reply:Rule is /Do all your killing at Spring time/when the weeds are young/no prob,rest O Season.
Reply:I just applied a weed killer that said the ideal temperature and conditions is greater than 60 degrees F and sunny. It's been cool around here (50+ during the day and low 40s at night) and it took about a week for the weed killer to take effect. I don't know if that was a temperature thing or what. Usually, it takes effect within 24 hours.





It's my experience that broadleaf weed killers for lawns don't immediately kill the weeds. It just stops them from growing. They then turn red and eventually die a few weeks later.





I would think a pre-emergent is fine any time, as long as the ground isn't frozen. You're essentially just sterilizing the seeds.
Reply:That surprises me too. Broadleaf herbicides work best when the plant is actively growing.





the preemergent might okay in your area right now. Around here (mid ohio) we recommend mid-March. You want it present BEFORE the seeds germinate, and if your temps are warming up now - you could have weed seeds germinating in the next few weeks.