Iím going to offer my $.02 here. I would agree that your best bet is to use concentrate Roundup. Mix with water per directions and use PPE. Rubber gloves, long sleeves, pants and rubber boots if you have them. Roundup is not as safe as Monsanto would like you to believe. Wash your clothes separately from the families.
Apply once and wait 7-10 days to find the areas you missed. Reapply to those missed areas. Wait another 7-10 days. Do not seed immediately after applying Roundup. Wait 3-4 days.
While youíre waiting for your beautiful bent grass to die select a nice northern cool weather grass mix. If you intend to water then a blend of 3-4 improved bluegrass varieties and 2 varieties of perennial ryegrass will work. If you want a lower maintenance lawn look for a mix that includes more fescues and less bluegrass (the bluegrass requires more nitrogen and water.). No need to add oats or annual rye if you select a mix with some good perennial rye blend.
Take your mower and cut the now dead grass as short as you can. You can mulch it (preferred) or bag it. Mulching leaves the clippings which help to retain water and protect your new seedlings.
Rent a slit seeder and overseed the lawn applying half the seed in one direction and the other half 90 degrees to the first. The slit seeder will cover the seed properly, no need to use a scarifier on your mower deck. They tend to put a lot of stress on the bearings and seals of your motor or spindle causing premature wear and failure.
Roll the area after seeding to make sure you have good soil and seed contact. You can apply a starter fertilizer now or after the seed germinates.
Water to keep soil moist for best germination. Twice a day every day for 30 days is best. Your ryegrass will germinate in 7-10 days. Bluegrass 15-30 days. The ryegrass will provide shade for your bluegrass seedlings. Keep watering after germination just not twice a day or every day. Your new seedlings need moisture and food to survive. You should wait until the grass is 3-4 inches tall before your first mowing. You might also want to give it another shot of starter fertilizer 30-45 days after germination.
Mow high (3+ inches) to shade out weed species and develop deep roots. Apply herbicide as needed but not before the new grass has hardened off. Maybe after 6-8 cuttings or better yet wait till next year. Make sure your blades are sharp and if you can use a push mower for the first few mowings. Never cut off more than 1/3 of the blade length. Frequent mowing will give you a denser turf.
Regular watering, fertilizer and herbicide as needed will give you a beautiful lust green lawn you can be proud of.
This is a picture of my backyard. I had the same situation as the OP and followed the exact method I just described. This lawn is about 22 months old and is irrigated and gets 5 applications of fertilizer a year.
Hope this is helpful.
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