Well, you have used a preemergent before - that is what Halts is. It lasts 2-3 months depending on the weather. Heat and moisture break it down quicker.

When to apply depends entirely on the type of weeds you are trying to prevent. For instance, crabgrass won't germinate in cold temps, so you should apply the preemergent right before it starts to warm up in spring. Some weeds germinate in fall and just stay tiny all winter before really starting to grow in early spring.

Yeah, for crabgrass (germinates right around 50-55 deg F) you need to apply right before the temps get high enough for them to germinate.

I've never used a post-emergent, but I hear they don't work nearly as well as pre-emergents do.

I don't see crabgrass on my lawn until it gets really hot, like in July. Then I just yank it out.

Hey All

Thanks for the comments. I have several types of weeds, crabgrass is one, but not as bad as Oxalis. I think I read here that Oxalis has tubers, but not sure. They do put out seeds -- the turtle doves love them around my house. I also take it that an application now, not knowing all the weeds I have, may be a good thing. Also I'll need to apply in late winter around here to be sure I get it down early enough -- no fertilizer yet because of the Zoysia. Thanks again,

Mike