If it were me, and there is a pretty big difference in the seed size, I'd probably go over it twice with a spreader; once with one seed type, and then once again with the other.

Hi, My home is located in Chicago and I am planning to over seed the lawn this fall. I would like some advice on what type of seed mixture I shall use based on the information below. 1. I believe that current my lawn has a mixture of blue grass, rye, and fescue. 2. The lawn has 3 main areas. The front yard is south east exposure with almost no tree shades. The side yard is west facing with 4 middle sized trees. The back yard is north west facing with no trees in the center areas(only has trees on the boundary. 3. In the summer, I only plan to water once a week if necessary. I do not plan to water heavily in summer to keep perfect green lawn. 4. I will do weekly mow and fertilize 3 to 4 times a year. Based on the information above, shall I choose 80/20 blue grass/rye mixture or 40/30/30 blue/rye/fescue mixture? Also, a side question, the lawn has some tall fescue invaded in the several spot in the front yard. It does not blend well with current mixture. If I just dig out the affected area and replace with sod, will that keep them out? Do I need to apply roundup to kill them then replace with sod?

Not really that hard to find, both can be found on Amazon. Prodiamine Tenacity Also at http://www.domyownpestcontrol.com/ if you prefer. It's a bit of an expense upfront but they will both actually save you money. Without Tenacity you will have an explosion of weeds as soon as you seed and start watering, it will cost you a lot to control selectively after the fact and ruin your lawn. There is a starter fertilizer available at Home Depot which contains the same active ingredient, however it will cost you ~$150+ for your size area. If you get the Tenacity bottle for $60 and starter fertilizer separately it will come out to about the same but you will still have half the bottle left for subsequent weed control and seeding projects. The Prodiamine jug will last you 10 years and cost $6 per spring app at 6 month rate. The equivalent protection with Home Depot products would cost you $100 per spring app at 6 month rate, so the Prodiamine jug will save you $940 over the next 10 years. With that size lawn a tow behind sprayer would be a wise investment. Also, it would be worthwhile to keep looking into buying bulk lawn care products( e.g herbicide concentrates, fertilizers etc.) rather than stuff from big box stores, it gets very expensive when you have that many square feet to cover.

Don't till, it's not necessary. My advice would be to skip any herbicide this spring and let the weeds come in full force. You can put down any remaining KY31 seed as well. Mow the weeds/KY31 through the summer to keep it looking nice. Round-up everything in the fall and re-seed.