If you dormant seeded, I wouldn't spray WBG until you've mowed the new grass twice.

Weeds are best controlled when they are actively growing. The toxicity of weed killers act on the leaf tissue taking it down through its system to the roots where it causes injury and death. If the weed is dormant, it could take much longer for the toxicity to be drawn into the leaf. Same reason why water is not so much needed during winter---the plant is unable to take it in. Considering the cost of herbicides, it does pay to get bang for your buck. Wasting it on something that cant appreciate it is money and effort wasted.

Speaking of baptism by fire...I hope the rest of your experiences with GW are better than this one. Y'all got off track early and it went downhill from there. You can have a weed free, low maintenance lawn, and do it without routine use of Weed-B-Gone. It is a matter of 1) growing grass that is suited to the location, 2) proper watering, 3) proper mowing, and 4) regular fertilizer. You are trying to hit todays issues but you have the recent memory of last year's issues weighing you down. I'm going to focus on this year's issues. The current symptom seems to be that your grass is too thin and it is allowing a variety of weeds to come and take over. Can you find the bag of seed you bought and tell us what the Guaranteed Analysis part of the bag says? I'm hoping that will explain the entire block of problems so far this year. I'm also hoping it will suggest a solution to be implemented in the fall. Fall is by far the best time to seed in the north. If you seed in the spring (early or late) there are weed seeds sitting there waiting to germinate. When you put in grass seed, all the weed seeds will germinate, too. You can prevent the summer weed seeds from germinating by seeding in the fall. Then in the spring you will be using a mature turf care program. That involves keeping the soil relatively dry and providing a tall grass to shade the soil. Keeping weed seeds dry in the spring can be hard with Mother Nature helping to water, but if you gain some sort of control over the moisture, then you should water deeply once every 1-2 weeks. Get out the hoses and sprinkler (I like an oscillating sprinkler). Keeping the grass tall seems to be your nature so that's good; however, when you do mow, mow at the highest setting on the mower. Auteck has not explained why he suggested mowing at 2 inches, but over the years the general consensus here at GW is that really tall grass is much better than anything else. Four inches works better for keeping weeds out and reducing your summer watering requirements. In the summer when the heat really hits, you can go without mowing for a month or two, but you should still water every week or two. The second problem with seeding in the spring is the new grass plants cannot tolerate the summer heat. Could that be why your lawn died last summer? Fall seeded grass has all winter and spring to develop deeper roots that can stand the heat and low moisture. Regardless of what the weeds are, you have some and need to get rid of them. The reason you have any weeds at all is your turf is not very dense. I am questioning auteck's idea that you have Kentucky bluegrass, because you should not have that thin a turf with KBG - unless that was what you seeded with this year (need the Guaranteed Analysis). The "dandelion" weed should die with WBG, but since it has not, I'm going to suggest that you fertilize right now, and then in 2 weeks, try the WBG again. Weeds that are not very healthy will not absorb the WBG and can even resist it. I know it seems crazy to fertilize the weeds so you can kill them, but that is exactly what I'm suggesting. Again, this is the consensus of Internet forum users over the ages. If you don't have a favorite fertilizer, look for a fertilizer like plain old Turf Builder that does not have any other additives like herbicide or insecticide - just fertilizer. If you are interested in an inexpensive organic lawn care program, here's a link to one. Also, it looks like you live in the woods. Does your lawn get much sunlight during the day in the summer? It must get enough for "crabgrass" to grow. True crabgrass needs full sun or it won't do well. Whatever your weed is, it acts exactly like crabgrass and looks much the same. I'm okay calling it crabgrass. I've been reading here for years and it always surprises me how early crabgrass appears in various parts of the country. My approach would be to discourage it with proper watering and mowing and to tolerate it (meaning no herbicides) one more season with anticipation and the hope of getting such a dense lawn next year that it will not come back. Yes, it can be done. For the fall, would you consider hiring a landscaper to resurface your entire lawn? In one morning he could fix the spots where the trees were, give you the best drainage possible, and prepare the soil for new seed. It would be a complete renovation which is why I don't suggest you spend a lot of money killing weeds this season. However, I'm not saying you should abdicate lawn care either. Treat the lawn as if it was the perfect lawn (despite the weeds) and it will surprise you. I should say that since you are not lawn people (yet, and I'm optimistic you will be), I have some doubt about the quality of the grass seed you have already purchased. It is very easy to buy a bag full of weed seeds when you are not experienced at reading the bags. It would be a shame to renovate and get the same problems back.

Don't know your region, but 3 years ago our 20,000 sf lawn of mostly KBG, in southern New England, was infested with ground ivy - or Creeping Charlie. After some research I found that WBG was the best remedy. I followed the label directions and applied with an Ortho Dial'N Spray applicator. If I recall correctly, the mix ratio is 2 oz. per gallon per 500 sf. I bought the gallon concentrate and broadcasted the application in divided quadrants of 5,000 sf. The best time to apply is when the weeds are flowering, or as was my situation, just about now. I must say, it did the trick and killed about 85-90% of all the weeds, even clover. Problem with ground ivy though, is it comes back. I've noticed it's spreading again but have been reluctant to reapply the chemicals, due to our large organic vegetable gardens, located in the middle of the rear lawn. I'm sure other, more knowledgeable posters, will provide better feedback, but in my experience it did work - by following label directions.