If perennial weed populations are very high, it may be necessary to fallow the field for a year, using a combination of tillage and herbicides to return the field to a condition suitable for other crops. Weed management is most effective when herbicides are used in conjunction with cultural practices. To avoid a buildup of resistant weeds, use preemergent herbicides in combination or alternated with another preemergent herbicide. Keep an inventory of the weeds encountered and their relative abundance in the field. Such a record can be helpful in planning which cultural techniques will be most helpful and which herbicides are most likely to be successful.
Perennial weeds can be a major problem in asparagus plantings.
Select alternative fields for asparagus if yellow or purple nutsedge, johnsongrass, bermudagrass, swamp smartweed, or field bindweed are present. Fallow the field for as long as possible before planting, irrigating often to germinate weeds and cultivating shallowly to destroy them. Do not cultivate too deeply as a new supply of weed seed may be brought up from deeper soil layers. Before planting, metham or a combination of methyl bromide and chloropicrin are often used as soil fumigants to control soilborne diseases and nematodes, but these materials can also be used to control annual weeds and reduce perennial weed propagules. Take care to assure that the soil is well cultivated and moist for at least 1 week before an application of metham.