Killing weeds & planting grass
Is there a product out there that would allow me to kill off the lawn weeds w/o killing off the grass, & not have to wait 3-6 months to reseed? A variety of weeds widespread, spot spraying not realy practical.
Your best route to the lawn you want depends on what percentage of your lawn is mostly weeds and what type of weeds they are. If your lawn is more than 50% weeds you should consider a lawn renovation.
Info on that is found at this link from our website. (Pay particular attention to the Lawn Renovation and Overseeding publication listed for all the steps):
Control methods are different for different classes of weeds. Some weeds germinate in the fall, bloom and set seed now, then die back for the growing season. Others get started right now and die with frost. Some are perennial, returning year to year, which others live only one season, but bank many, many seeds in the soil so they can return each year.
The need to wait for a period of time before reseeding suggests that you are talking about what is called a pre-emergent herbicide application, like that which is commonly used in the spring to try and stop crabgrass from germinating. Crabgrass is one of our most common grassy weeds, and it is the one most people try to stop in the spring. (We recommend using not a Weed-n-Feed type product, but just the 'weed' component. (Pendamethalin). Lawns are better fertilized in the fall). Spot treating is used primarily for broad-leaved weeds, and for some perennial grassy weeds like nimblewill, it's recommended to kill back the entire patch in the fall and reseed.
Late summer into fall is the best time to re-seed or renovate.
Read through the pages on the weeds you have. Some tend to show up when your underlying conditions (too wet/shady or compacted) or lawn management (poor pH, cutting too short, not leaving the clippings on to decompose) and you could work on correcting some of those now.
Starting with a soil test: http://extension.umd.edu/hgic/topics/soil-testing
The soil test will show your pH and what soil amendments should be made for best results.
You can id what weeds you may have and how to best control them by looking at photos here: http://extension.umd.edu/hgic/topics/lawn-weed-id-and-management