Stuff is horrible and used in pasture mixes as it can be decent feed for cows. Here is a good link on it.
An aid for Johngrass identification and maintenance practices that also points out the benefits and drawbacks of weed in pastures.
extension.okstate.edu
I find that many weeds, like smartweed - can be controlled by controlling the PH of the soil. This is not an end-all-be-all fix but can help tremendously reduce the population density of the weeds. Combine that with herbicide applications in the beginning, and we can have a major positive impact on the reduction.
Johnsongrass however, is very well adapted to a wide range of soils -
"Johnsongrass is adapted to a wide range of soil types within a pH range of 5 to 7.5. Therefore, Johnsongrass is mainly found in arable lands, orchards, open waste grounds, roadsides, pastures, irrigated canals and ditches. "
Just another plant we should try to control.
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