Those small blue flowers are on the henbit weed, a cool-season annual. Henbit also makes larger purple flowers. Henbit and chickweed got their names because chickens like to eat them. Yum, yum. Henbit is a mint and it has square-shaped stems, although I can't really tell that the stems are square when I look at them, just like it's hard for me to tell that sedges have triangluar stems, and I have good eyesight I think. Henbit will die as the temperature climbs. Before it dies and after the flowers show up, it will release seeds to try and grow back next year. This weed is easy to pull out of the ground. Not sure but I think the seeds might be found in small structures called nutlets that the plant produces. The nutlets are spherical things that are usually about 2 or 3 millimeters long. Sometimes I see them close to the ground. Henbit is prolific. Lots and lots of henbit. But on the positive side, it is easy to hand pull.

If you want to renovate (kill everything and start over with seed) then you should wait till late summer. If it was me, this is what I would do. Get your soil tested by a reputable lab. I recommend Logan Labs, get the standard test, $20. While you're waiting for the results I would try to kill all the weeds possible. Weed and feed products are NOT recommended. They are a way the fertilzer companies can charge you more for something you don't need. Get Weed B Gone Max and Weed B Gone Clover, Chickweed, and Oxalis killer, the concentrates, not the premixed. Read all labels. Get a tank sprayer. Mix the required amount of both in with the appropriate amount of water, and spray anything that you don't want in your lawn. Meanwhile treat your lawn like you are going to keep it. Frequent applications (monthly) of organic fertilizer like Milorganite, corn meal, soy meal, etc. will raise the organic matter levels in your soil. When the soil tests come back you will add things to improve your soil further. Wisconsin is Kentucky Bluegrass country, unless you don't have a lot of sun. KBG is very cold tolerant unlike perennial rye and tall fescue to an extent. What does the tag say on the bag of grass seed you bought say, i.e. the types of grass in the bag. If it isn't KBG, you might want to think about new seed. Timing is key in seeding grass. I live in CT, my time of seeding is around Sept. 1. I want to say you should be seeding around August 1, which means spraying round up mid July if you are doing one app, July 1 if you are doing 2 apps. Once everything is dead, then mow the dead stuff as low as possible using the bag attachment on your mower. Personally I like to power rake after you mow. It loosens up the soil, and breaks up some of the dead roots. Some people don't like to because they feel like it brings up weed seeds, but you will get some weeds either way, it's your call. After the power rake I manually rake everything smooth. Then I seed at the appropriate rate (don't think more seed is better, it's not). Then I roll the seed with a water filled roller. I like to topdress my seeds, it's not necessary, but I think you get better germination, and your risk of seed wash out is lessened with heavy rain. Then you can roll again since you rented the roller already. You can top this off with shredded straw if you want, again, not necessary, but it can prevent wash out even more, and it will become organic matter in the long run. Then I like to apply a half app of starter fertilizer. Then you water three to four times a day, for 10-15 minutes to keep everything moist, but not soaking wet. Once the grass hits about 3 inches then you can mow it down to 2.

Cultural solution first. Water deeply and infrequently based on the grass. When it looks thirsty (won't spring back after stepping on it or looks dry) then water at least an inch. Put a small can (tuna cans are ideal, but anything will do) in the area of the sprinkler so you know how much your putting down. Cut high with a sharp blade. Fertilize. It may be too hot for chemical fertilizer. If you don't have an aversion to Milorganite it would be ideal. Apply at the rate on the bag. Some may offer that fertilizing is wrong, but from your description the grass is weak and it needs food. Feed the grass and kill the weeds is how I see it. Fixing the weeds. Before you apply the Menards product read the label to see if it is effective on crabgrass. If not, then your local big box should have a product that would work. Bayer and Ortho are pretty good products. Hose end sprayer seems to work well. Same stuff should be available in granular if you prefer spreading, but liquid seems to work faster. Just follow the directions. Towards the end of August or first half of September you should plan on overseeding (cut grass short gradually, core aerate, apply new seed and fertilize). There are several threads with some great instructions on renovation. Patience. It will take some time to heal. Renovation this fall will be your best time to improve the lawn.

I know what that plant with thorns is but the name escapes my mind... Yes it is true that sugar has positive effect on the soil to help fight off weeds. It doesn't exactly kill the weeds, it just makes the soil unsuitable for weeds as the soil improves dramatically as long as you do not do anything to destroy the soil like chemical fertilizer, anything that ends with icide. Organic lawn program is the way to go. When we say sugar, we usually means unsulfured blackstrap molasses (packed with nutrients) which causes explosive growth in microbe population in the soil sucking up excess nitrate (a form of nitrogen) that weeds need to thrive. When nitrate level is low enough, you shouldn't have much of weed problem. YOu should get a book called Teaming with Microbes by Jeff Lowenfels. I think it is the best book to introduce organic practice (lawn, garden, etc) for anyone wanting to convert to organic ways.