Originally Posted by ted putnam
Greendoctor. I wanted to respond to this the other night but found myself waiting for a couple of answers from Skipster. I guess I'm not going to get them from him.
If I were in your situation(12 month growing season), it would seem that once I had a lawn thickened and weed free, I would most likely find it unnecessary to apply much if any pre's except in high pressure areas of certain lawns. I mean once they are established and stay on your program, there should really be no need for pre's right?...just regular maintenance that includes spot spraying.
The only thing living in our bermudas at least 3 months of the year are stolons and rhizomes in the thatch layer. This leaves the lawns susceptible to seed germination of broadleaf weeds all the way from the time they are going in to until the time they are fully out of dormancy. IMO, pre's are absolutely necessary here. If not for the crabgrass, for everything else that is looking for a way in when the bermudas are at their weakest...
I do have some rare zoysia lawns that do not belong where they are because there is barely enough sun for them during the "summer" months. In the "winter", the sun shifts and the days get short causing the lawn to be light deprived. Those are the lawns that are treated with a grass preemergent and Gallery in November. Failure to do so results in crabgrass and broadleaf weeds everywhere. Those people are cut a lot of slack by me because what is causing this problem are trees surrounding the lawn. My instructions concerning irrigation and mowing are followed. The trees are only strike one.
You are quite right about a thick lawn. My idea of thick is complete coverage of the soil and no stems or stolons visible. Stems or stolons visible means the height of cut is wrong. Which is why I have a cow when St Augustine is scalped and bermuda or zoysia is cut over an inch.
In a well managed lawn, the only thing that comes up is purple nutsedge. Its emergence is fostered by rain followed by hot weather. Removal of that normally takes 2 years. Thinking past just killing leaves and understanding the weed helps. That is a weed I do not spot spray. Effective herbicides are also active through the soil, so not treating the whole area leaves the weed free to emerge elsewhere.