bobm
Garden Master
Easy ? Well , I had put down 3 sheets of 20' x 20' black plastic down then several dozen pallets over them then bring in 100 tons / year of alfalfa hay and stacked the bales 16 bales high for 3 years to cover stinging nettle and crab grass near our creek and under a 300 year old oak tree on my ranch. After 3 years, I removed the black plastic to replace the badly torn sheets that spring and after a nice rain guess what came back up ? Now for mustard ... my neighbor has a 17 acre field that every spring when the mustard grows to 5-12 inches tall he then discs the entire field twice to kill off the young plants, then plants barley + wheat . By summer his field is almost solid sea of yellow with mustard blooms. He cuts the barley/wheat crop at the dough stage but before the mustard seed is ripe and bales the barley/wheat hay as feed lot cattle feed that he sells to another neighbor. He has been doing this for each of the last 18 years.I've downed bitter nightshade, stinging nettle, mustard is easy, crab grass is easy and many other plants.
The basic idea is this, can the plant go two years without sunlight? The cardboard prevents photosynthesis for about that long which kills the plant. With bitter nightshade, I cut it to the ground, cover it with cardboard, then mulch, wet it all down and never see it again.
This doesn't work for everything but it should be sufficient for the home gardener.
Humorously enough this method was pioneered in Australia. Look into the work of David Holmgren and Bill Mollison.