Hi Jennifer!
Your first lawn application of Weed Prevention Plus should be in the early spring, 3-5 weeks before weeds begin to sprout. This is about the time the crocus and daffodils are blooming in your area. Re-apply in late summer when temperatures turn cooler to control late season weeds.
When used as directed, Weed Prevention Plus will not harm beneficial insects, soil organisms, pond, or stream life. There’s no waiting, warnings, or worries. As for coverage, each 25 lb bag of Concern Weed Prevention Plus handles 1,500 square feet of ground so, in order to cover half an acre, you would need 14.5 bags.
To answer your last question, there is not a whole lot you can do this time of year, except to spot-treat with organic herbicides and hand pull. AllDown Organic Herbicide is a safe alternative to Roundupยฎ. This 23% vinegar weed killer is trusted by cities and municipalities, the US Fish and Wildlife Service, orchards and many other agencies across the country. However, it is non-selective and will work on any plant it touches, including most weeds, grass or broadleaf specimens.
Good luck!