I think weed barrier in general is a bad idea, but especially on slopes. The cheap stuff tears if you have to walk on it. It can be slippery and dangerous on hills. If you lay down mulch to cover it, unless the mulch is rock, it breaks down and the weeds just grow in that. Rock collect dirt and the seeds just grow in that. Luckily the weeds are fairly easy to remove from the mulch.

I would just do a couple of grow/kill cycles with glyphosate, then plant with a preemergent. Weed growth will be minimal after that. They can then be controlled with preemergent until the groundcvoer fills in. When you pull weeds out of weedy ground, you just bring up more weed seeds to the surface where they will sprout. The grow/kill cycles sprout and kill a lot of the existing surface seed load. The preemergent will help rot out anything that is brought up from planting.

Yes, use a pre-emergent and repeat regularly according to package directions until the myoporum is thoroughly established and dense.

It really depends on the types of weeds, and also your soils type and how you intend to irrigate long term. The dwarf pink form of Myoporum parvifolium can take light foot traffic, does root along the stems in good soil with sufficient moisture, and absent aggressive perennial weeds such as Cynodon dactylon, Blackberries and similar, it can effectively fill in completely and minimize new weed growth of the type that blowns in. I generally use surface drip emiiter line under mulch when I've planted this Myoporum, and it filled inwell within 6 months planted out from flats at 12" o.c. Dealing with weeds first, amending soil to improve growth, and providing sufficient irrigation to get it established, along with pre-emergents all help.

Thank you so much. My weeds on this slope are all annuals and I plan to install drip irrigation so your recommendations sound like a great plan.

I only use drip on really narrow or oddly shaped planting areas where I can't use a low precipitation spray head. If the area to be irrigated is a fairly decent sized rectangle I use MP Rotators from Hunter. They were designed to be resistant to wind andnot cause runoff on hills. Installation is much easier than drip line, and it's ometimes possible to use existing popups. Drip line also has the problem of needing to either be completely level or completely covered with mulch so as not to concentrate flows. The drips will run down the tube instead of falling down into the soil. This can lead to erosion and or uneven irrigation. Plus when you have a plant that will root along its stem, you want even irrigation across the planting area to encourage that rooting.

What are the rough dimensions of the plating area?