Opening ditch lines

[Fladogman]

70 hp on a 5' non-offset rear blade, hmmm, might work in Florida but doubt it will work around rocks. Need a 7 foot offset-able heavy duty one!
A pond scoop (dirt scoop) might work, and a middlebuster might break up the ditch so that you can use the 5 foot rear blade without tearing it up.
David from jax

Sandman is right, a heavy duty 6 way blade will do it but a light weight one probably will break or bend. If you don't have one or know where you can rent or borrow one then hiring someone to come fix it once might be your best option. Once fixed you can maintain it with a lighter blade.

 

[sandman2234]

Just for the record, I own an M7040... and I used to own a 5' non offset rear blade, and that was in Florida!
It caught a pretty good sized root and in a split second was transformed into scrap.
David from jax

 

[2manyrocks]

That looks like a solid practical answer.