An Etymological Dictionary of the German Language/Werg
Werg, n., ‘tow, oakum,’ from the equiv. MidHG. wërch, wërc (for the double form comp. Storch), OHG. wërah (hh), and wërc, n.; also OHG. âwirihhi, âwurihhi, n., ‘tow, stuppa.’ The OHG. and MidHG. forms of Werg are identical with those of Werf, hence the former is usually derived from the latter; this, however, does not explain the development of meaning. OHG. âwurihhi, ‘tow,’ may be connected with Werf and wirken, since it means ‘the refuse produced by work.’ Perhaps the simple word was developed from the compound.