Let the 'weeds' grow. Anything that is strong enough to put roots down in the earth of a slope that steep will help stabilize it. Stop spraying ! That poison is draining down into that ditch and onward to contaminate the creek and is toxic to every natural critter that drinks from the creek water.

I don't know if this has anything to help you with your project but I think you will find this interesting. You really need to research slope stabilization or you might wake up with a mudslide into your swimming pool. I would research why you can do to hold back the slope. This link is about Vetiver Grass and the Ho Chi Minh Highway. Great photos of destabilized soil and the use of plants to hold things back. Weeping Lovegrass is also used in erosion control. Weeping Muhlenbergia is used for erosion control . Personally I think this should have been talked about at the time of the sale as to the chances of slippage and checked by an engineer. That slope looks dangerous.

I agree with dottiecarrano; Let the weeds be! :) I live in Eastern KY as well and completely understand how difficult it can be living backed up against a hillside. However, I have found that trying to live in harmony with the hillside tends to work much better than battling against it. Why rid the hill of its natural vegetation just to replace it with something that may or may not like it there. The weeds might not be the prettiest thing to look at, but they're definitely better than a dirt wall (which is all you will continue to have if nothing else takes to it). I mean, if you want invasive you could bring in some kudzu or something (goodness knows we have enough of that around here), but I don't think you want to do that... lol But yes, all those sprays are creating toxic runoff and, if anything, are counterproductive to what you are trying to achieve. We've got some really pretty "weeds" here in EKY; Let 'em live. :)

I am working on a few steep hills as well, but my approach has been to only remove vegetation from an area I am ready to plant (and mulch). That gives me a chance to test the plants i'm introducing and isn't overwhelming. Let the weeds grow and just use loppers to cut saplings and shears if you can't stand the tall weeds. Get a big load of wood chips dropped off by a tree company. Plant one shrub, surround it with newspaper or cardboard, wet it and cover with your woodchips. That's your toehold. Make your mulch "apron" the ultimate size of the shrub, which will give you an idea of where you're heading. When you're considering the plants, think about their ability to hold the soil and also their ability to spread or be divided. That will make it financially viable. What do your neighbors do with their slopes?