Preplant weed control All major weed problems can be prevented by starting with a clean field and avoiding reinfestation. For proper preplant management, growers should consider spraying perennial weeds with several applications of an appropriate systemic herbicide, using sand free from weed seeds, fumigating soil, planting weed-free vines, cleaning equipment when moving between beds, and seeding dikes with cover crops effective in preventing weed infestation (e.g., dwarf perennial ryegrasses and some creeping fescues).
Year-round weed management in bogs Successful weed management in cranberries requires a comprehensive, year-round approach that alternates a combination of weed control practices over several years. Developing these strategies requires knowledge of each weed and weed control practice. First, identify weeds and gather information about the effectiveness of each weed control practice. Consider costs and select herbicide combinations that may be applied together or in split applications that control most weeds in the beds. Note each herbicide’s action within the plant (site of action). Then combine and alternate these products and other weed control practices to reduce the chance of developing resistant species or biotypes. Map the precise locations of different weeds in the bed to allow for spot application of herbicides. Removing weeds (especially perennial weeds) and seed heads by hand is often necessary, and should be done regularly. Mow dikes and other areas surrounding the beds periodically, to prevent weeds from spreading or reproducing by seed. Shape dikes to accommodate mowing equipment.
Applying herbicides Herbicides must be applied at the correct rate and time to control weed growth with minimal chance for injuring the cranberries. Recalibrate your herbicide applicator every year. For spot applications make sure that your tank-mix is based on spray volume. Follow guidelines in this handbook for backpack sprayer calibration. Results will be more consistent if you read the herbicide label and other information about the proper application and timing of each herbicide. Rates suggested in this guide are stated as pounds of active ingredient per acre (lb ai/a) or pounds of acid equivalent per acre (lb ae/a). Numerous products with the same active ingredient are labeled for cranberries. These products may have different concentrations of active ingredient. To avoid rate problems, be sure cranberry is on the label and follow the rate listed on the label. Avoid applying herbicides when water is standing on the soil surface. To minimize phytotoxicity and improve weed control, apply preemergence herbicides to dry vines, then water them in after application. At the beginning of each season, check with your Extension specialist to see whether a Section 18 for a new herbicide, or a SLN for a modification in the use of a currently registered herbicide has been granted. Also consult your handler for maximum residue limit (MRL) restrictions for export fruit.
Warning Using 2,4-D or similar materials on horticultural farms involves risk not only to the crop to which it is applied but also to crops in nearby fields. In some instances, however, careful use of 2,4-D enhances weed control with minimal chance for crop injury. Be careful to clean all 2,4-D from your equipment, otherwise use separate sprayers before applying another product to other horticultural crops. Never use a volatile formulation of 2,4-D or similar material. Buy only a product that lists the intended crop on the label.