Dimension 2EW is not labeled to be used in edible gardens. We do carry the Vegetable & Ornamental Weeder that is safe for that use though.
After application of Dimension 2EW Herbicide, you can reseed 3-4 months after application. Per label:
While Dimension 2EW Herbicide can prevent japanese stiltgrass when used according to label instructions, it would not control existing stiltgrass. Most applications for prevention will need to be made spring and fall for 2 years to prevent seeds that can lay dormant in the soil over time.
Pre-emergents like Dimension 2EW should be used before the weeds germinate in the fall time. We would recommend checking with a local master gardener in your area to give you an exact time. Here is the link:
http://www.csrees.usda.gov/Extension/
Please let us know if you have any additional questions.
Unfortunately their is not a selective product that will remove crabgrass from St. Augustine. St. Augustine is a very fragile grass, and so most selective products that are labeled to remove crabgrass and not your real grass, will hurt the St. Augustine. It is recommended to kill the crabgrass with a round up type product, like Ranger Pro, which will also kill just the St. Augustine around the crabgrass that it is sprayed on, and then a couple weeks later re-seed those areas with new St. Augustine.
Image 70 DG is labeled for the sandbur and white clover as well as crabgrass suppression though.
For long term control though, you should apply a pre-emergent in the late fall and early spring which will prevent new crabgrass from coming up next year. If you apply pre-emergent every year, you should not have issues with crabgrass long term. Dimension 2EW is one of our most popular pre-emergents for crabgrass. Dimension would also be good for the clover and stickers.
Yes, you will mix the amounts as specified on the label. It does not sound like a lot, but it is enough product to treat the area in at least two gallons of water.