Chemical herbicides are available for use on collards and are generally recommended. Whether you use a herbicide or not, some cultivation will likely be necessary. Avoid deep cultivation. Close spacing and rapid growth will help to suppress weeds. A rigid control program will be necessary, especially during summer and fall.
Aphids are also a serious problem during cool weather.
You should insist on western grown, chemically treated seed to reduce this disease. Another major disease is Downy Mildew which produces discolored spots on the leaves. The Carolina variety has resistance to one or more strains of Downy Mildew. Successive cutting can be done with these systems. These are tied in bunches of one to three plants with a rubber band, twist-em or string.