I've read where crabgrass germination usually happens when the soil has
warmed to about 50 degrees for a couple of days (there are less precise
indications, something to do with forsithia blooming).

I believe that grabgrass germination conditions has recently (or will
soon) occurr in my area (SW-Ontario - climate similar to Detroit,
Toronto, Buffalo, Cleveland).

Here is a web-link to the specific product:

http://www.scottscanada.ca/index.cfm...37186E06EAAA9E

So my questions with regard to this product a

1) This product seems to contain the following components:
- Dimension
- Halts
- Dithiopyr

What exactly are those chemical components? What is "Halts" ?
What does each chemical do?

2) How does the efficieny or longevity of this product change
or improve or degrade in relationship to rainfall after
application? Is some rainfall after application desirable?
Will too much rainfall reduce the effectiveness or longevity
of the product?

3) For how long after application will this product remain
active or usefull at killing emerging crabgrass shoots?