HAHA< I agree with the mowing, , mow that stuff while its still standing if you can, the chemical that kills it will hit the roots in a day or so
, so anytime after that you can pretty much mow it, longer the better, but before it lays down
heavy matted material on top will make SOME tillers struggle, depends on the HP of the tractor running it some things and quality of the tiller!
something you can do you MAKE your plot sites even better , IS< if SAFE
till the site into smaller squares, leaving material in small sections with a nice dirt barrier between things and burn them one at a time
just do it on a safe day, NO to low wind, (Looks like rain soon)and have some help handy in case anything flys!
I used to have a 55 gallon tanker sprayer with a wand that would help pout out anything SMALL
and the key here is SMALL squares, don't try burning large sections at a time, unless your willing to get your local fire dept involved, and MANY times they will , it gives them practice on fires!
its called controlled burns, and a major tool in habitat restorations and farmers been doing it for yrs to make lands more fertile
adds feed fertilizer/mostly potash, but it gets rid of all that material on top!
also NOT sure what your planning to plant, but some things you can also just burn down site(chemical burn down) and seed right thru it and use the material as protection from critters eating the seeds,
do so in a rain and most seeds will get seeded from he rain, no need to turn site over at all,
as turning over a site, you always turn over old seeds in dirt and then have them growing along with your desired new plantings!
sites don't always need to be tilled over or disc'd!